The objective of straw treatment is to increase the digestibility of straw and/or the amount of it voluntarily consumed so that digestible energy intake by animals from straw is increased. Methods of treating straw may be classified broadly into physical, chemical and biological categories. Among physical methods of significance are grinding and pressure cooking. Very fine grinding in ball mills and irradiation, while effective in improving digestibility, are so expensive that they are unlikely ever to become commercially significant. Chemical methods currently being developed all employ alkalis. Other chemicals like chlorine can also be used to improve digestibility but are more expensive and more difficult to handle than the alkalis and no technology involving their use has yet been developed. The alkali treatment methods may be classified as follows.
Modified Beckmann (Torgrimsby) (NaOH)
Industrial process (NaOH)
Farm scale treatment
Daily treatment (NaOH, Ca(OH)2, NH3)
followed by stacking (NaOH)
followed by ensiling (NaOH, Ca(OH)2)
of stacks under plastic sheet (NH3)
Wet methods involve soaking straw in 10 litres of chemical solution per kg of dry straw. In dry methods straw is sprayed with 0.1 to 3 1 of chemical solution per kg of dry straw or exposed to ammonia vapour. Wet methods employ a higher ratio of chemical to straw than do the dry methods. In biological methods the aim is to increase digestibility of straw by culturing certain specific types of fungi on it. Each of these methods will be described and its effectiveness assessed.
An essential preliminary, however, will be to describe the factors affecting the digestibility of straw per se. Much new information, some unpublished, is now available on this subject. This information is indispensable to a correct assessment of straw treatment.
The causes of variability in the digestibility of straw when fed to animals are:
intrinsic causes (specie, variety, environment, methods of harvesting and handling)
the way the straw is fed to animals (diet composition and level of feeding)
If the straw is treated then a third factor is the efficiency of treatment. This will be discussed separately for each of the methods dealt with later in this section. The first and second are discussed in the following paragraphs.
Some digestibility and energy values for straws are presented in table 1. Variability is large both among species of straw and within species and there are few clear-cut consistent differences. In Europe wheat and rye straws are considered by scientists and farmers alike to be poorer than barley and oats straw. This is in a general way borne out by the data in table 1, but the variability within species (see ‘D’ value, column 4) makes it possible to get samples of wheat straw which are better than some samples of barley straw in the same year from the same area. Much of this is due to varietal differences as evidenced by the data for the T.D.N. values of Canadian straws (column 7); the crops were all grown in a single, replicated field experiment. Similar varietal variability has also been reported from India by Kharat (1974) for wheat and by Saleem and Jackson (1975) for paddy. There was no difference between older, long-strawed varieties and newer, short, stiff-strawed varieties in these two studies. In Britain it is commonly believed that spring barley straw is more digestible than winter barley straw and the Ministry of Agriculture, Food and Fisheries tables (column 9) give metabolisable energy values of 7.3 and 5.8/kg, respectively. Recent British data (column 4) does not, however, support this contention, nor does recent French data (column 2). Maize stover seems to be superior to other straws.
Straws also vary in the amounts in which they are voluntarily consumed by animals. Mulholland et al. (1974) fed oat, wheat and barley straws ad libitum to sheep and recorded dry matter intakes of 600, 400 and 300 g/day, respectively. Intake was positively correlated with organic matter digestibility in vitro. Urea supplementation increased the intakes of all three straws, but the relative differences among them remained.
The digestibility of straw is affected by how it is harvested and subsequently handled. Leaves are more digestible than stems in all straws (except paddy, in which the reverse is true; Saleem and Jackson, 1975) and thus the height of cutting the crop at harvest influences digestibility. Xande (1977) found that straw picked up from the field immediately after combining had a higher digestibility by about 2 units than straw that was left in the field for some time. This is presumably due to leaf loss and possibly to leaching losses where rain falls on the combined straw before it is picked up.
|Straw||Organic-matter digestibility||‘D’ value||Enzyme digestibility||T.D.N.||M.E.||S.E.|
(1) Norway. %. Homb, 1947.
(2) France. %. Xande, 1977.
(3) Denmark. Organic-matter digestibility in vitro, %. Rexen, Isrealsen, Busk andWaagepetersen, 1975.
(4) U.K. Digestible organic matter in dry matter. Alderman, 1976.
(5a) Denmark. Danish straws. % of dry matter digested. Rexen et al., 1976.
(5b) Denmark. Indian straws. % of dry matter digested. Rexen et al., 1976.
(6) U.S.A. kg/100 kg dry matter. Morrison, 1959.
(7) Canada. kg/100 kg dry matter. Kernan et al., 1977.
(8) India. kg/100 kg dry matter. Sen and Ray, 1971.
(9) U.K. Metabolisable energy. MJ/kg dry matter. MAFF, 1975.
(10) U.K. Starch equivalent. Watson, 1941.
Busk and Kristensen (1977) sampled a large number of bales from one field and determined the enzyme digestibility of each sample. The average was 28 with a range of 19 to 32.
The significance of the differences in initial digestibility is that they remain after alkali treatment. This has been most clearly shown by the experiment of Rexen, Isrealsen, Busk and Waagepetersen (1975). Nine lots (each of 500 kg) of each of 4 types of straw-winter barley, wheat, oats and rye-with initial average values for organic matter digestibility in vitro of 50, 49, 55 and 44, respectively (see column 3 of table 1) were chemically treated with different amounts of NaOH (0–8 kg/100 kg straw) and pelleted. All the straws were improved by increasing amounts of alkali at about the same rate and initial differences remained at all levels of treatment. Similar results have been reported by Piatkowski et al. (1974a). It is therefore likely that differences in the digestibility of treated straw of as much as 10 units could be caused by differences in initial digestibility alone. Differences of this magnitude might occasionally even occur among samples of treated straw of the same specie.
Wherever government extension services provide a feed testing service to farmers, the testing of treated straw by an in vitro or enzyme solubility technique could be instituted. Such test values would indicate initial digestibility plus treatment effect and could be used to formulate specific feeding recommendations for individual farmers. In this connection the enzyme solubility method developed in Denmark (B.Rexen, 1977) would appear to be useful.
It is widely recognised that the supplementation of roughage with starchy feeds reduces the digestibility of the roughage. The rate as well as the extent of digestion is affected. The results of an experiment done by Chimwano et al. (1976) with dried grass and concentrates demonstrate this (table 2). The voluntary intake of a roughage is also reduced. Lonsdale et al. (1971) added barley to a dried-grass diet to the extent of 50% and found that for every 1 kg of barley consumed dried-grass consumption decreased by 1 kg. Thus dry-matter intake did not increase by adding barley to the diet. They also found that the retention time of cellulose was increased as well as the dry-matter content of the entire alimentary tract. These changes seem to account for the lower intake of the dried grass observed. Straw digestibility and intake have likewise been shown to be reduced by concentrate supplementation (table 3 and 4). A further conclusion which can be drawn from the data shown in table 3 is that a roughage supplement, even a high-quality one like dried grass, does not depress straw digestibility as a concentrate supplement does.
In two recent experiments (Piatkowski et al., 1973; Rexen et al., 1975b) the digestibility of treated straw was not found to be depressed by high levels (50%) of concentrates in the diet. Straw was treated with 4–5 kg NaOH/100 kg. These results are not incompatible with the conclusion arrived at in the preceeding paragraph. In the experiments of these two groups of workers, treated straw was fed at restricted levels. It is widely recognised that the level of feeding a roughage affects its digestibility (review by Blaxter, 1961). Increasing level of intake depresses digestibility and the depression is greater with less digestible roughages like straw than with more digestible ones. The results of a recent experiment done by Dulphy et al. (1977) (table 5) show how important level of feeding is with treated straw. At a restricted level of feeding digestibility was not only higher but also did not decrease when increasing levels of concentrates were included in the diet. This finding clearly shows why Piatkowski et al. (1973) and Rexen, Stigsen and Kristensen (1975) did not find any decrease in the digestibility of straw when they increased concentrate levels.
|Proportion of concentrate in the diet,%||Dried grass: loss in weight,|
(g/100 g) after:
|Cotton thread: loss in weight, |
g/100 g after
|6 h||12 h||18 h||24 h||24 h|
|SE of treatment means||3||3||3||3||5|
Source: Chimwano et al., 1976.
|Type of Supplement||Amount of supplement, %of diet||Organic-matter digestibility of straw, %||Dry-matter intake, g|
|(soyabea n meal and maize)|
|(soyabean meal and maize)|
Source: Dulphy, private communication-1977.
Blaxter et al. (1961) showed that the depression in the intake of roughage varied with the quality of the roughage; with a high-quality dried grass, 1 kg of concentrates reduced intake by 1 kg, but with a lower quality (i.e., lower digestibility) dried grass 1 kg concentrate caused a reduction in intake by only 0.49 kg. Presumably the digestibility of the high-quality dried grass was depressed more than that of the low-quality one. A practical implication of this finding is that the difference in digestibility and overall feeding value between a high-and a low-quality grass hay or silage is less in a production diet containing a high level of concentrates than is indicated by the results of digestibility trials. The data from a recent experiment with straw shows that this does, in fact happen; with concentrate supplementation the digestibility of treated straw is depressed more than that of untreated straw (table 4). Due to this differential rate of depression in digestibility, the apparent difference between treated and untreated straw in digestibility is reduced as the level of concentrate supplementation is increased; it can be decreased to zero with 40–50% concentrates. This is a likely explanation for at least some of the observations made from time to time that the alkali treatment of straw did not apparently improve its digestibility, or improved it only a little (see review by Jackson 1977). Similarly, in some experiments where liveweight gains have not improved by the treatment of the straw in the diet, the differential effect of concentratesin depressing straw digestibility may be responsible. A further systematic study of this phenomenon should be given the highest priority in research programmes on straw utilisation; it should be given a high priority even in programmes of research on conventional roughages like hay and silage.
The amount of nitrogen in the diet also affects the degree of improvement in digestibility that occurs as a result of alkali treatment. Donefer et al. (1968) measured the effect of urea supplementation (2.5%) on the response of alkali treatment (8 kg/100 kg neutralised with acetic acid) of ground oat straw fed to sheep. Energy digestibility increased by 13.5 units when no urea was given and 18.3 units when it was. Voluntary intake of straw was depressed by 19 g/kg W0.75 on alkali treatment when urea was not fed, but increased by 31 g when urea was added. φrskov (private communication--1977) measured the effect of increasing levels of urea on the digestibility of treated and untreated straw. The maximum digestibility for treated straw was obtained when 1.2–1.8% urea was added; the digestibility of untreated straw, on the other hand, did not increase with the addition of urea. Kategile (1977) fed a diet of ground, NaOH-treated, maize cobs (90%) and molasses (10%) to heifers and varied the amount of urea added from 0 to 1.25%. Digestibility of dry-matter increased linearly from 39–60%.
|Level of supplementary concentrate, % of diet||Organic-matter digestibility of straw, %||Dry-matter intake, g/day (60 kg sheep)|
* 4 kg NaOH/100 kg straw
Source: Breton, private communication fromDulphy--1977.
|Level of supplementary concentrate, % of diet||Organic-matter digestibility of straw, %||Dry-matter intake, g/day|
|Intake ad libitum|
* 4 kg NaOH/100 kg straw
Source: Dulphy et al., 1977.
To assess the effectiveness of any straw treatment technique, the difference between the digestibility of the untreated and treated straw must be determined. From the foregoing discussion it is clear that if this difference is measured by digestibility trials with animals it will be influenced by the following factors.
The effectiveness of the treatment
Any difference in the level of feeding between the untreated and treated straws. If the animals are fed ad libitum, the voluntary intake of the treated straw will usually be higher than that of the untreated straw. This may decrease the difference in digestibility obtained.
The type and amount of other feeds/supplements in the diet. Too much easily-fermentable carbohydrate or too little protein/nitrogen will decrease the difference in digestibility obtained.
It is apparent that if the objective is to assess the effectiveness of a treatment technique per se,the best way to determine the difference in digestibility is by an in vitro method. Such values are not influenced by the animal at all, and are reasonably reproducible (Sundstol et al., 1977). Considerable reliance is therefore placed on in vitro values in this report. At the same time, treatment techniques must be assessed for their effectiveness in improving the feeding value of straw in the types of diets in which the straw is to be used in practice. The only completely adequate way to do this is by conducting feeding trials in which the performance of animals is measured. Changes in digestibility and intake can be determined at the same time. If full-scale feeding trials are not feasible for preliminary investigations, simpler digestibility and intake trials may be done, but the diets should be those that would be used in a feeding trial. Where an untreated straw diet is the local practice, such a diet should be compared with a similar diet in which the straw has been treated. If the objective is to determine whether treated straw can replace another feed in the local diet, then three diets must be included in the trial. The first is the local diet. In the second and third diets untreated and treated straw, respectively, are substituted for one of the components of the local diet. Examples of this type of trial are those conducted by Pirie and Greenhalgh (1977) (on beef steers) (paragraph 62) and by Bergner et al. (1976) (on milking cows) (paragraph 56). Many trials conducted to date have either been digestibility trials comparing untreated and treated straws in a diet that is irrelevant to the prevailing local feeding practices, or feeding trials in which treated straw, but not untreated straw, has been substituted for another feed in a local diet. In the second type of trial it is assumed that the treated straw is better than untreated straw, but, in view of the evidence presented earlier in this section, this assumption may not always be valid.
The subject of grinding of roughages was critically reviewed by Greenhalgh and Wainman in 1972. With all-roughage diets, grinding causes an increase in intake and weight gain. These effects are greater for roughages with lower digestibility; however, nitrogen can be a limiting factor to improvement by grinding for very poor roughages like straw. Grinding usually decreases digestibility, but at the same time increases the net energy value of the straw somewhat because the nutrients that are digested are utilised more efficiently by the animal. This improvement in net energy value may be more marked with poor quality roughages.
The grinding of straw appears to give much less improvement in feeding value than alkali treatment, at least in terms of digestible organic-matter intake. This is evident from the data in table 6. In general terms also, grinding does not increase digestible organic matter intake by more than about 30% (review by Greenhalgh and Wainman, 1972), whereas alkali treatment increases it by up to 100%(e.g., table 19).. The improvement in the netenergy value of straw by grinding might narrow the difference in terms of net-energy intake, but is unlikely to alter the conclusion that alkali treatment is about twice as effective as grinding in increasing the feeding value of straw. The effect of grinding is also much less or even nil when straw comprises 50% or less of the diet. What remains to be considered is the effect of grinding in conjunction with alkali treatment. The results of an experiment conducted by Fernandez Carmona and Greenhalgh (1972) indicate an additive effect of grinding and alkali treatment (table 6). The digestible-energy intake by sheep on a ground and alkali-treated straw diet was 15% greater than on a diet of chopped alkali-treated straw. Feeding trial data are needed to determine if grinding in addition to alkali-treatement is economically worthwhile. The grinding of straws before alkali treatment in some straw-processing plants is done to facilitate the subsequent mixing of the treated straw in commercial concentrate mixtures (paragraph 51).
|Untreated straw||Treated straw+|
|Organic-matter digestibility, %||45||61|
|Dry-matter intake, g/kg W0.75||27||48|
|Digestible energy intake, Kcal/kg W0.75||46||114|
|Organic-matter digestibility, %||45||64|
|Dry-matter intake, g/kg W0.75||36||54|
|Digestible energy intake, Kcal/kg W0.75||60||132|
* The straw was supplemented with purified soyaprotein at the rate of 8 g/100 g straw. Thedigestibility of this supplement was assumed tobe 100%--data are for straw only.
** Straw chopped into 2–3 mm lengths
*** Straw milled in a hammer mill through a 2 mm sieve
+ Straw spray-treated with 8 kg NaOH/100 kg andneutralised with 7.4 kg propionic acid
Source : Fernandez Carmona and Greenhalgh, 1972.
The pressure cooking of sugarcane bagasse and wood chips has been found to increase digestibility. Donefer and pathirana (1976) treated samples of bagasse with 4% NaOH and with high pressure steam (8 kg/cm2 at 170°) and found increases in cellulose digestibility in vitro of 15 and 17 percentage units, respectively (initial digestibility 25%). Higher pressures and temperatures than these give still greater increases in digestibility. A company in Canada has developed equipment for pressure-cooking wood chips. Increases in digestibility in vitro are reported to be from 15–20% to 50–60% for aspen tree chips (Stake Technology Ltd., Canada, private communication--1978). Treated material has a dry-matter content of 55% and a pH of 3.5–3.8. The low pH is due to the release of organic acids during treatment. Guggolz et al. (1971) pressure cooked grass straws at a pressure of 30 kg/cm2 and found an increase in digestibility in vitro of 20 percentage units. When they added 3 g NaOH/100 g straw before pressure cooking the increase was 40 units. When the same group (Garrett et al., 1974) treated rice straw in this way and fed it to sheep, digestibility and intake were reduced when NaOH was not added, but were increased when it was. Even then pressure cooking with NaOH was no better than NaOH treatment and heating for 15 min to 100°. Possibly the temperature was too high, causing charing of the pressure-cooked straw. When they treated bagasse in this way they found a large increase in phenolic-like compounds (Campbell, 1973). Somewhat lower temperatures might give useful results. If this method (without NaOH) is as effective on straws as the best NaOH treatment methods, it merits further study. One advantage it has over alkali treatment is that it contains no residual solium. The disadvantages are its high moisture content and the fact that capital investment might be too high for small farms.
Interest in the chemical treatment of straw revived in the 1960s with the introduction of the dry treatment method in which straw is simply sprayed with a limited volume of an alkali solution. This development overcame the obvious disadvantages of the older Beckmann method of high water requirement and high dry-matter losses, and made the industrialisation of straw treatment possible. The fact remains, however, that the quality of Beckmann-treated straw is higher than that of spray-treated straw. It is therefore a welcome development that modified Beckmann methods have been devised which reduce or eliminate dry-matter loss and hence environmental pollution. Water requirement is also drastically reduced. To obtain a proper perspective on these modified Beckmann processes, the original method will first be described and commented upon.
A very interesting review of the early research on the alkali treatment of straw and the development of the Beckmann method has been presented by Homb et al. (1977). The earlier reviews by Homb (1947 and 1956) are also recommended. There has been a tendency to overlook the results of this valuable earlier work. The chemistry of straw treatment was reviewed recently by Jackson (1977).
The scale of operation and the degree of mechanisation of the Beckmann treatment process vary widely, but in all installations two tanks are employed. The straw is immersed in a 1.5% solution of NaOH for 18–20 hours. The volume of solution is 8–10 l. per kg of dry straw, which is enough to cover the straw, and provides 12–15 kg NaOH/100 kg straw. After 18–20 hours, the treatment solution is pumped to the other tank and fresh water is pumped in. The wash water overflows into a drain when the tank is full. This washing continues for 18–20 hours after which the tank is drained. The straw is then ready to be fed. Straw is treated in a loose or baled form and chaffing is unnecessary for treatment or for subsequent feeding; on the other hand long baled straw is easier to handle during treatment than chaffed straw. The used NaOH treatment solution, after being transferred to the second tank, is made up to volume (by adding about 300 1 water/100 kg straw) and NaOH strength (by adding approximately 8 kg NaOH/100 kg straw). In most plants the volume of the treatment solution is made up with the first wash water from the first tank to economise on alkali. In this way net consumption of alkali is about 6 kg/100 kg straw. The next day, the treatment solution is pumped back to the first tank again and thus one batch of treated and washed straw is produced every day. In the Norwegian installations, both cooperative and farm-scale, the straw is lifted into and out of the tanks with travelling, electric chain hosts. Some further details of the operation of the Norwegian co-operative straw-treatment plants are given in paragraph 131.
The Beckmann treatment may also be done manually on small farms, as was recommended before the mechanised versions came into use in the 1950's (eg., Watson, 1941). The treatment solution remains in the same tank and the straw is transferred to the second tank which is used for washing only.
Treated straw contains about 20% dry matter and is limp. The nodes should be soft; in fact the softness of the nodes is a simple hand test applied to straw to determine the effectiveness of treatment. Well-washed straw should not feel slippery or soapy. The sodium content is 0.5–0.6% on a dry-matter basis (0.07-0.16% in original straw); the legal limit is 0.3%. Dry-matter losses are 20–25 kg per 100 kg original dry-matter. The digestibility and feeding value of Beckmann-treated straw are discussed later in paragraphs 37–40.
The effectiveness of the treatment depends upon time, temperature, pressure and amount of alkali. The effect of amount of alkali used on the digestibility of treated straw is shown by the results of an experiment done by Fingerling et al. (1923) (table 7). Twelve kg NaOH/100 kg straw may be near the amount needed to achieve maximum increase in digestibility. In the spray-treatment process maximum increase in digestibility in vitro is achieved with about 10 kg NaOH/100 kg straw. Fernandez Carmona and Greenhalgh (1972) found that the digestibility in vitro of treated straw increased linearly upto a level of 14 kg/100 kg straw (2% solution) and levelled off thereafter. Piatkowski et al. (1977) have found a large additional increase in digestibility when the amount of alkali was increased from 10 to 20 kg/100 kg straw by increasing concentra tion from 0.5 to 1.0 (20 volumes of solution used;soaking for 24 hours). In many of the cooperative plants in Norway 20 kg or more of NaOH/100 kg straw is routinely used (15–18 volumes of a 1.5% solution), the managers feeling that these quantities of NaOH are needed to give the soft texture they aim at in treated straw. The exact amount of alkali needed in any situation wil depend upon the length of time the straw is soaked, the environmental temperature and the nature of the starting material. The influence of time and temperature are discussed in the following paragraphs. No experimental data is available on the relative alkali needs of different types of straws for maximum increases in digestibility, but cooperative treatment plant managers in Norway use a greater amount of alkali to treat wheat straw than to treat other types to get comparable texture in the finished products. Fortunately, the use of a sizeable excess of alkali is feasible since all but about 6 kg NaOH/100 kg straw is recovered in each treatment cycle whatever the amount present in the treatment solution.
|Organic matter digestibility, %|
|Treated straw, 2 kg NaOH/100 kg||46|
|Treated straw, 4 kg NaOH/100 kg||50|
|Source: Fingerling et al., 1923.|
The effect of time on treatment effectiveness is revealed by the results of an experiment done by Fingerling and Schmidt in 1919 (table 8). As a result of this experiment a soaking period of about 20 h became the recommended practice. Ferguson (1943) later found that this period could be reduced to 7 h in the summer in England without reducing the effectiveness of treatment, but not in the winter. He also found that 4 h soaking and 19 h draining were not as good as 23 h of soaking (the starch equivalent values calculated from digestibility trial data were 47.6 and 51.2, respectively).
|Organic matter digestibility, %|
|Treated straw,||1.5 h||59|
Source: Fingerling and Schmidt, 1919.
An effect of environmental temperature was also found by Ferguson (1943) (table 9). The results of the extensive study done by Ololade et al. (1970) (table 10, right-hand column) indicate that still further increases in digestibility can be obtained if the treatment solution is heated upto the boiling point. Boiling was a feature of various pre-Beckmann methods, a feature that was dropped because it added unduly to the treatment cost.
|Temperature, degrees||Digestibility coefficient,%|
Source: Ferguson, 1943.
The advantage of the Beckmann method is that it gives a finished product of high digestibility. Some organic-matter digestibility values have been presented in table 11. Increases on treatment range from 14–27 percentage units. The range for straw treated by dry methods is much lower (see paragraph 67). The main reason for the effectiveness of the Beckmann method is the high ratio of alkali to straw it employs, a ratio of 12 or more kg NaOH to 100 kg straw, and the fact that the excess is washed out. When straw is treated by the dry methods not more than about 5 kg NaOH per 100 kg straw can be used, at least when straw constitutes a major part of the diet (70% or more). This is because excess alkali is not washed out. Somewhat more alkali can be used if the straw constitutes 50% or less of the diet, but even then the increase in digestibility of dry treated straw does not go beyond the range 15–20 units. The disadvantages of the Beckmann method are, of course, the high water requirement, dry-matter loss and river pollution. The treated straw is heavy (80% water) and must be prepared every day.
|Temperature||Processing duration||Sodium hydroxide (% of dry matter)|
* Each value is a mean of 3 replicates; for processing at 23° thepooled SE is 0.57 and HSD 3.24 at the 5% level of probability,while for processing at elevated temperatures these values are0.63 and 3.31, respectively.
Considerable variability is evident in table 11 in the degree of improvement in digestibility obtained with the Beckmann method. This variability is even found among different trials reported by an individual author. In Norway an increase in digestibility of 18 units was obtained on an average in 4 trials (42 to 60--see table 11).
|Country||Type of straw||Organic matter digestibility, %||Reference|
|Germany||46||71||Fingerling and Schmidt (1919)|
|46||73||Fingerling et al (1923)|
|Barley||45||71||Fernandez Carmona and Greenhalgh (1972)|
Later farm trials gave average treated straw digestibilities of 66 (for unchopped straw in 5 trials) and 68 (for chopped straw in 10 trials). The average value for treated straws from all 19 trials was 66, but the range was from 56–76 (Homb, 1947). Some further data on the variability in the digestibility of treated straws has been given by Ferguson (1943) (table 12).
|Type of straw||Number of digestibility trials||Organic matter digestibility, %|
Source: Ferguson, 1943.
Two production experiments in which treated and untreated straw were fed are known to have been conducted. One was done on Indian village heifers by Kehar and is described in paragraph 88. The other was done by Saxena et al. (1971). They fed growing lambs diets containing 78% straw and 22% of a concentrate supplement. The results are shown in Table 13.
|Untreated straw||Treated straw||Untreated straw||Treated straw|
|Soyabean meal||Soyabean meal||urea||urea|
|Feed intake, g DM||870||1290||820||1110|
|Daily gain, g||62||177||53||125|
|g feed/g gain||14.6||7.3||15.3||8.8|
Source: Saxena et al., 1971.
Beckmann-treated straw has been prepared and fed to livestock on farms in Norway for the past 40 years. The usual amount of treated straw fed to milking cows is 15–20 kg per day or 1/3 to 1/2 of the roughage offered. Heifers, bulls and steers are fed 8–16 and occasionally even 24 kg straw per day. In feeding trials with milking cows, treated straw was found to be equivalent to good quality grass silage in calculated net-energy value (Homb et al., 1977).
Several experiments have been done to compare the use of Ca(OH)2 and NaOH for the treatment of straw by the Beckmann method (Abou-Raya et al., 1964; Abou-El-Hassan et al., 1971). Though Ca(OH)2 is a strong alkali like NaOH, it has been found to be less effective in increasing digestibility (table 14). This is probably because it is only sparingly soluble in water. Its use has also been investigated with dry treatments and the findings will be referred to later (paragraphs 63 and 75).
The most immediate problem with the Beckmann method was that of river pollution. If wash water could not be discharged, it would have to be recycled. Torgrimsby (1971) suggested a closed system in which the amount of water added to the system is equal to the amount removed in the treated straw. The method was further developed by Wethje (1975) and is being successfully used on his farm in Sweden. Preliminary experiments have been conducted at the Agricultural University of Norway in which the system has been run for 6 months continuously, producing a batch of treated straw every day. Evaluation of the straw is being done. This method is described in detail in paragraphs 44–48 below.
|Alkali used||Maize stover||Sorghum stover|
|Crude fibre||N.F.E.||Crude fibre||N.F.E.|
Source: Abou-Raya et al., 1964.
At the same time, several experiments have been done at various places with the Beckmann method modified only in that less wash water was used. Piatkowski et al. (1977), for example, treated straw with 20 l of a 1.5% NaOH solution per kg straw for 24 hours in the usual way. The straw was then washed with only 4 l water/kg straw. Organic matter digestibility increased from 46 to 72% (restricted intake, limited supplement). The sodium content of the treated straw was 2% and dry matter losses 13%. Obviously only a partial solution to the problems associated with the Beckmann method is achieved; water requirement is reduced, but dry matter loss and river pollution are not eliminated altogether. The prospect of this modified method developing into an environmentally acceptable and economically viable proposition is therefore poor.
The Torgrimsby method, on the other hand, though still not extensively tested, hold much more promise. The easiest way to visualise the operation of this process is to consider how it would work on a small, unmechanised scale. Three tanks are needed, each with an attached drain board (figure 1). Tank A contains 1000 l of a 1.5% NaOH solution in which 100 kg straw in bundles or bales is soaked. The first rinsing tank B contains 2000 l of water and the second rinsing tank C also contains water (1000 l). Tank B is twice as long as tanks A and C (see “top view”). To the right of each tank in the diagram is a sloped drainboard (a, b and c). The straw could be lifted in and out of the tanks by hand or with a hand block-and-tackle on an overhead rail. The daily sequence of operations is as follows:
Figure 1. Arrangement of treatment tanks for treatment by the modified Beckmann (Torgrimsby) method. Straw is moved from tank to tank--refer to paragraph 44.
|07:00||Remove treated straw from A and place on a to drain (the straw was placed in A the day before at 12:00).|
|08:00||Remove drained treated straw from a and place in B. Place fresh (dry) straw (100 kg) in B as well.|
|12:00||Make up NaOH concentration of A by adding about 4 kg NaOH. Remove fresh straw from B and place in A. Remove treated straw from B and place on b to drain.|
|13:00||Remove treated straw from b and place in C.|
|16:00||Remove treated straw from C and place on c to drain.|
|17:00||Transfer 300 l of water from C to B to make up the volume of the latter (the 100 kg fresh straw removed 300 l water earlier).|
|18:00||Wash treated straw on drainboard C with 300 l fresh water by pouring the water over the straw (This runs into C, thus making up its volume). After this final washing, treated straw is ready to feed.|
The foregoing is intended as an example; numerous variations are possible. The essential features are:
Soaking for 19 hours in a treatment solution containing 15 kg of NaOH/100 kg straw as in the Beckmann method
the alkali washed out of the treated straw in tank B reacts with the fresh straw in the same tank, thus pre-treating it while at the same time increasing the removal of excess NaOH from the treated S raw
a final washing with 300 l of fresh water
the only outgo of material from the system is 300 l water and about 4 kg NaOH/100 kg in the straw every day.
These amounts of water and NaOH are added daily. There is no loss of dry matter from the straw and no straw dry matter accumulates in the system.
The treated straw has a dry-matter content of about 20% and a sodium content on a dry-matter basis of about 2% (Sundstφl, 1977, personal communication). Dry matter digestibility in vitro increased on treatment from 38 to 70. This increase in digestibility of 32 units may be compared with an increase of about 17 units in the dry industrial process when 4 kg NaOH are used per 100 kg straw (paragraph 53).
It will be seen that this method retains the advantages of the Beckmann method, except that the removal of excess alkali is not quite so complete, while at the same time overcoming all the disadvantages. The increase in digestibility in vitro of 32 units and the fact that there is only about 2% sodium present suggest that the treated straw is as high in quality as Beckmann straw, but digestibility and feeding trials must be conducted to determine if this is so.
The Torgrimsby treatment process may be mechanised, as indeed the pilot plant at the University of Norway is. The following description is only an example of the possibilities. Four tanks are needed, two treatment tanks and two auxillary tanks (figure 2). The straw remains in one of the two treatment tanks throughout the process, the treatment solution and washing water being moved from tank to tank by gravity and by pumping. One thousand litres of treatment solution (1.5% NaOH per 100 kg straw) and two lots of wash water, also in a proportion of 10:1 are employed. The daily sequence of operations is:
Treatment solution is drained from tank A to tank C.
Figure 2. Arrangement of treatment tanks for treatment by the modified Beckmann (Torgrimsby) method. NaOH solution and wash waters are transferred from tank to tank-refer to paragraph 48.
|07:00||Starting position: Straw is soaking in treatment solution in tank A, having been placed there the previous day. Wash water I (first wash water) is in tank B and wash water II (second wash water) is in tank D. Tank C is empty.|
|08:00||Fresh straw is put into tank B. Wash water I in B is then pumped to tank A where it is continuously sprayed over the treated straw and recycled back to B.|
|12:00||Wash water I is retained in tank B. Wash Water II is pumped from tank D to tank A. Wash water I is drained from tank B to tank D. Treatment solution is pumped from tank C to tank B and its strength made up by adding fresh NaOH.|
|15:00||Some of wash water II in tank A is drained into tank D to make up the volume of wash water I, and the remainder is drained into tank C. Sufficient fresh water to make up the volume of wash water II is sprayed on the treated straw in tank A and allowed to drain into tank C. The treated and washed straw in tank A is now ready to feed.|
|The starting position is: Straw is soaking in treatment solution in tank B, wash water I is in tank D and wash water II is in tank C. Tank A is empty. The day's operations begin by pumping wash water I from tank D to tank A and draining the treatment solution from tank B to tank D. Fresh straw is then placed in tank A and the sequence of operations of the previous day proceeds.|
With such mechanisation the process could be scaled up to almost any size, or at least to the size of the present-day co-operative Beckmann treatment plants.
The development of dry chemical methods of straw treatment was also approached from point of view of improving upon the Beckmann method. The improvement was that the treated straw is not washed. Consequently only as much NaOH can be used as will not unduly disturb the animal system. This level of NaOH has been found to be about 5 kg/100 kg straw. Thus, while, the problems of dry-matter loss and river pollution are solved by the dry method, the benefit from the use of a high alkali: straw ratio (i.e., a large increase in digestibility) had to be foregone. By applying heat and pressure some of this loss in the degree of improvement in digestibility can be recovered, but the most efficiently dry-treated straw under the best circumstances is still inferior to the best wet-treated straw in digestibility. Moreover, sodium pollution is not eliminated, but only occurs in a more diffuse form when straw is treated by the dry method. On the other hand, a very great advantage of the dry method is that it can be industrialised, as indeed it has been. The wet methods can only be used on a farm or local community scale, and even then the labour requirement to treat and feed wet-treated straw is a distinct disadvantage in Europe and North America where labour is expensive.
The subject of the health of livestock fed on dry-treated straw has been discussed by Jackson (1977). In general, animals suffer no stress if the diet contains less than 4% of NaOH on a drymatter basis. This corresponds to 2.5% sodium in the diet.
Scientists at the Biotechnical Institute at Kolding in Denmark have developed a factory method for the treatment of straws and have built a successful pilot plant. This development work has been described by Rexen et al. (1975a) and by Rexen et al. (1975b). These publications are recommended for a detailed understanding of the factory method. Only a brief description will be given here.
A simple process-flow diagram of a straw processing factory is given in figure 3. It is a composite of the designs of the several commercial plants visited by the consultant. The capacity of these plants is 4–5 tonnes of straw treatment per hour. Straw is delivered to the plant as bales which are unloaded on to a concrete apron. They are then pushed by a tractor with a front-mounted loader on to a conveyer leading to a tub grinder, or lifted and placed directly into the grinder. Bale strings (sisal or plastic) are not removed but are processed with the straw. From the tub grinder, the straw is elevated to an intermediate holding bin. This bin acts as a buffer to even out variations in rate of intake. In some plants and automatic switch stops the intake conveyor when this bin fills to a certain level; the conveyor is again switched on when the level falls. Again in some plants, but not all, the straw is dried to about 13% moisture content, if necessary, by electric heating coils in the elevator between the tub grinder and the intermediate holding bin. The heating coils are operated automatically by a sampler and moisture tester in the system at a point just before the treater mixer. By drying the straw the throughput of the plant is kept uniform and near maximum. In those plants which do not dry the straw, throughput fluctuates widely with the moisture content of the straw. In the moist climate of Northern Europe, straw delivered to the factory usually has a moisture content of about 20%, if not rained on, but there is a wide variation and plant output can be reduced considerably at higher moisture contents. Against this loss is, of course, the saving in heating costs. Aside from the question of throughput, straw with a moisture content of more than about 23% heats up less in the pellet press and forms poorlycompacted pellets. From the intermediate bin the straw goes to a hammer mill for milling in some plants, or directly to the alkali treater in others. While there is a lack of evidence for a significant nutritional or economic benefit from grinding (paragraph 27), ground straw may be preferred if the treated straw is subsequently to be used in commercial concentrate mixes. Equally dense pellets can be made from milled as from chopped straw, though more power is needed to make a given size pellet from chopped than from milled straw; 8 mm diameter pellets are commonly made from milled straw and 16–25 mm pellets from chopped straw. If the straw has been milled it is blown into a cyclone and from there it passes into the alkali treater; otherwise it passes directly to the alkali treater from the intermediate holding bin. Just before entering the treater, the straw passes over a band weigher which regulates the rate of addition of the alkali solution. Alternatively, the weigh band is placed after the pelleter. The treater in most factories is of the type developed at the Biotechnical Institute, Kolding and has been described by Rexen et al. (1975a). It has been designed to ensure a uniform application of the alkali solution to the straw when the rate of application is only 10–15 l (of a 30–45% solution of NaOH) per 100 kg straw. Simpler ways of applying the alkali are in use in some plants-for example, the alkali solution is dribbled on the straw passing through a screw conveyor--but mixing of lye and straw is less uniform and efficiency of alkali usage is poorer. Further, a black gum-like cake develops on the inner walls of the conveyor and on the screw thus reducing throughput. From the treater, the straw is conveyed to the pellet mill. Pelleting increases the density of the straw from about 50 to 500 kg/m3. It also causes heating (due to friction) of the straw to about 90°. The heating and pressure to which the straw is subjected increases the effectiveness of the treatment (see figure 4). Aside from a simple effect on the rate of chemical reactions occuring in straw, pressure in the press probably also causes an immediate and complete penetration of the alkali into the straw particles. Heating the alkali solution and adding steam in the pellet mill give a small further increase in digestibility, but are not apparently worthwhile in practice. A very firm pellet is obtained as the cohesiveness of the straw particles is increased by NaOH; molasses is not needed as a binder. The pellets are finally cooled and stored. In some factories the pellets are left hot for 15–20 minutes after coming from the press before being cooled in the pellet cooler because experience has shown that they sometimes heat up again in the store if cooled immediately; apparently the reaction between NaOH and straw is not always complete when the pellets leave the press. Factories which produce pure, treated-straw pellets, sell them to feed compounders who grind them up and include them in conventional concentrate mixtures. A limited amount of these pellets are sold to farmers. In other plants, however, the treated straw is used as only one ingredient in a complete pelleted feed. In these plants, therefore, molasses and other feedstuffs (cereals, brans, oilcakes, etc.) are added to the treated straw before it is pelleted. Where this is done, effectiveness of the treatment of the straw is reduced (Rexen, personal communication--1977), but this adverse effect can be counteracted to some extent if the alkali solution is heated to 90° before being applied and steam is injected into the mixture when pelleting.
Figure 3. Process flow diagram of straw treatment by the industrial process (refer to paragraph 52)
The digestibility in vitro of 88 samples of straw processed in the Kolding pilot plant using different amounts of NaOH from 0 to 7 kg/100 kg of straw has been determined. Simple linear regression analysis of this data has yielded the following equation: Y= 49.27 + 4.28 X, where Y is digestibility in vitro and X is the kg of NaOH used per 100 kg straw (Rexen et al., 1975a). Thus the use of 7 kg of NaOH increases potential digestibility by about 30 percentage units. Higher levels of NaOH than 7 kg may not give further increases judging by the results of the experiment of Ololade et al. (1970) (table 10--compare figures for 8 and 12 kg NaOH for 80° and 5 minutes). In digestibility trials with animals in which factory-treated straw has formed 70% or more of the test diets, digestibility has increased with increasing levels of alkali upto only 4–5 kg NaOH (Rexen and Thomsen, 1976; Ali et al., 1977), presumably because the high sodium content and alkalinity begin to impair physiological function of the animal. At a level of 4.5 kg alkali, which has been subsequently adopted in most commercial plants, digestibility in vitro is increases by 20 percentage units. In vivo increases were 16 units in the two experiments referred to above. Factory-treated straw has a sodium content of about 2.7%. pH is above 10 and titratable alkalinity is equivalent to 1–2 kg NaOH.
A number of feeding trials have been conducted with factorytreated straw (Rexen et al.. 1975a: Andersen. 1977: Bowerman, 1977; Wilson and Brigstock; 1977). In many of them only one diet containing a proportion of treated straw was fed. In two, treated straw was substituted for other components of the diet. One of these trials was with milking cows, but the data on actual milk yields is not given. In another, with beef animals, feed intake was not measured. These substitution trials thus provide little concrete information which could be used to assess the usefulness of factory-treated straw. In only two trials were treated and untreated straw compared. In one, a trial with growing bulls fed 30% straw diets, no difference in weight gain was found. Because of the high proportion of concentrates in the diets in this trial, there may not have been any difference in digestibility between treated and untreated straw. In another trial, one with growing heifers fed diets containing 60% straw, the untreated-straw group gained at a rate of 0.67 kg/day and the treated straw group at a rate of 0.79 kg/day. This data gives an indication of the value of treatment, but does not provide any information that will help in deciding whether or not farmers could use treated straw in a conventional hay/silage and concentrate diet for heifers. A large proportion of the production of straw-treatment plants in Europe is presently being used as an ingredient in commercial concentrate mixtures at rates of between 5 and 20% of the mixtures. There is no information to date on the value of treated straw used in this way.
Figure 4. The effects of time and of pelleting on the digestibility of straw treated by the industrial process (refer to paragraph 52).
Source: Rexen et al., 1975.
Many experiments have been done in which dry-treated straw has been neutralized with acid before feeding it. In most of these experiments this was done only on the assumption that it would improve the feeding value of the treated straw. A few comparisons have, however, been made between unneutralised and neutralised, treated straw. Rexen et al. (1975b) fed cows at restricted levels on factory-made straw pellets (containing only urea and mineral supplements) and similar pellets which had been neutralised with HCl. The straw pellets were presumably made in two stages in order to spray the HCl on and mix the supplements. Organic-matter digestibility increased by 3 percentage units and palatability, assessed by eating behaviour, was improved. The same pattern was also observed when the straws were mixed with concentrates in a ratio of 1:1. Junker and Pfeffer (1976) found an increase in intake of factory-made treated straw (5% NaOH) of about 5% by neutralising with 5 l of propionic acid per 100 kg straw. Greenhalgh et al. (1973) reported, on the other hand, that farm-scale, daily-treated straw neutralised with propionic acid was no better than un-neutralised straw in an experiment with sheep fed ad libitum. Raine and Owen (1976) fed sheep ad libitum on alkali spray-treated straw (3.5, 7.0 and 10.5 kg NaOH/100 kg straw) prepared and fed daily which was unneutralised or neutralised partly or completely with HCl. Concentrate supplementation amounted to 20% of the diet. Neither intake nor digestibility were significantly affected by neutralisation at any level of treatment. Thus there does not seem to be sufficient improvement in feeding value to warrant the extra expense of neutralisation. It may also be added that the utilisation of treated straw, as it is usually fed in Europe, would likely be improved by making it more alkaline and not less (paragraph 62).
A variation on the factory process using NaOH has been developed in the German Democratic Republic (Bergner et al., 1976; Bergner et al., 1974a, 1974b and 1976; Muller and Bergner, 1975; Muller et al., 1976). Sodium hydroxide is not used; urea is mixed with the straw at a rate of 2% before being pelleted. If the temperature during pelleting is increased to about 150°, the urea is decomposed and the NH3 released reacts with the straw, increasing its digestibility and nitrogen content. In one experiment (Bergner et al., 1974b) the organic-matter digestibility (by sheep) of chaffed straw was increased from 38 to 52 by this process. Organicmatter intake (from the straw part of the diet only) increased from 10 to 29 g/kg W0.75. In a milking cow experiment (Bergner et al. 1976) untreated straw or straw treated with 2% urea and 2% NH4 CO3 were fed as the sole roughage and in a third diet hay and roots were fed as roughage. The performance of the cows(yield level 6–15 kg milk/ day) on the treated straw was as good as that of the cows on the traditional diet of hay and roots. The food intake, milk yield and fat percentage of milk of cows on untreated straw fell in comparison. Crdinary pellet presses do not develop sufficient heat during pelleting to decompose urea. The machines used by these workers presumably have smaller openings and/or thicker dies and accordingly, a higher power requirement. The method looks promising, but the consultant does not have enough information to assess its practicality or economic feasibility. Ammonia is, in general, less effective than NaOH, being a weak alkali (see paragraph 80), but does add extra nitrogen to treated straw at the same time as the straw is treated and does not cause pollution).
Farm-scale treatment methods are those that can be used on the individual farm. They are simple and equipment costs can usually be paid by the individual farmer. These costs vary from a few (US) dollars for a garden sprinkling can and a hay fork to about $ 10,000 for one of the Danish farm machines. The methods vary in their effectiveness and the reasons for this will be highlighted in the following paragraphs. There appears to be great opportunity for further improvisation; a few suggestions will be given in this report itself.
Dry straw is sprinkled or sprayed with a dilute NaOH solution so that it is uniformly wetted. It is desirable to feed the straw the day after it is treated as digestibility increases significantly with time over the first 24 h after treatment (Ololade et al., 1970; Owen, 1978; fingerling and Schmidt, 1919). A fresh batch is prepared every day. The operation may be done by hand where only a few animals are to be fed using a sprinkling can and_a_fork to turn the straw whilst it is being sprinkled. For complete and uniform wetting, experience suggests 200 l of solution per 100 kg straw. If a pressure sprayer is used this can be reduced to 100 l. For treating larger batches of straw a horizontal feed mixer or a “mixer-trailer” designed to mix silage and concentrates may be fitted up with a pump and spray nozzles. In this case uniform wetting can be achieved with 50 l of solution. Other ingredients in the diet can subsequently be mixed with the straw in the same mixer. Other equipment might be devised. For example, a specially-designed screw auger with spray nozzles inside would give a continuous flow of treated straw.
This method is the simplest of all the farm scale methods, but is unfortunately less efficient. This is clear from the results of in vitro studies. Ololade et al. (1970) treated straw with an initial digestibility of 42% with 4 g NaOH/100 g straw (table 10). Digestibility increased to 54 when kept at 23° for 24 hours, but to 60 when heated to 80° for only 15 minutes. In the industrial process (paragraph 52) and the bulk treatment and stacking method on the farm (paragraph 71) both, a similar increase in digestibility in vitro occurs as a result of the heating the straw is subjected to following spraying with alkali. Straw-treated by the dailytreatment, dry method has never been compared with these other methods in a single digestibility trial with animals, and comparisons among trials are difficult. An attempt may however be made. Straw treated daily with 4–5 kg NaOH/100 kg fed ad libitum with limited concentrates has rarely been found to have increased in digestibility by more than 10 percentage units. In the experiments of Rexen and Vestergaard Thomsen (1976) and Ali et al. (1977), however, the factory-treatment of straw increased digestibility by 16 units when fed ad libitum to sheep in diets containing 30% concentrates. To achieve this degree of improvement in digestibility with the daily-treatment method, much greater amounts of NaOH are apparently needed. In an experiment by Fernandez Carmona and Greenhalgh (1972) in which sheep were fed diets containing 92% straw treated with 8 kg NaOH/100 kg, digestibility increased by 16 units. In a later experiments (Greenhalgh et al., 1976; Pirie and Greenhalgh, 1977) with straw fed in lamb and beef fattening diets at levels of 50 and 40% the organic-matter digestibility of the straw was increased by 18 and 20 units, respectively, when treated with 8 kg NaOH/100 kg. Even in this latter experiment, however, digestibility increased only 2.25–2.5 units/kg NaOH compared to 3.9 in the experiments of Rexen and Vestergaard Thomsen (1976) and Ali et al. (1977).
Straw treated by this method is moist, has a pleasing yellow colour and a smell of caustic soda. Animals eat it readily and when fed ad libitum usually eat 10–20% more of it than of untreated straw. The pH is 10 or above. Sodium content increases approximately 0.6 g percentage units for every 1 kg NaOH/100 kg added. When treated with 4–5 kg NaOH/100 kg, titratable alkalinity will be equivalent to 1–2 kg NaOH and at 8 kg the amount will be about 4 kg (Chandra and Jackson, 1971; Piatkowski et al., 1974; Fernandez Carmona and Greenhalgh, 1972; Rexen, Isrealsen, Busk and Waagepetersen, 1975).
The results of a number of experiments have shown that in diets where straw constitutes 70% or more of the diet, the least amount of alkali that will give the maximum increase in digestibility is in the range 3–6 kg/100 kg (see review by Jackson, 1977). In a more recent experiment in which treated straw was mixed with berseem forage in a ratio of 1:1 on a dry-matter basis, digestibility increased significantly upto a level of 9 kg NaOH/100 kg straw (Naik and Singh, private communication --1977). It would thus appear that the potentially higher digestibility of straw treated with more than 6 kg NaOH can be realised in diets in which the straw, with its high alkalinity and sodium content, is diluted with other feeds. Since even this high level of alkali gave economical increases in growth (of heifers) (table 16), it is suggested by the consultant that NaOH treatment levels can profitably be increased to 7–9 kg where straw constitutes only 50% or so of the diet.
|Dry-matter intake, kg||Empty body weight gain, kg||Milk yield, kg||Fat content, %||Total solids, %|
|LAMBS (36 kg initial weight)|
|Untreated straw diet|
|Treated straw diet|
|STEERS (300 kg initial weight)|
|Untreated straw diet|
|Treated straw diet|
|All concentrate diet||7.88||1.16|
|Untreated straw diet|
|Treated straw diet|
Source: Greenhalgh et al. (1976) for lambs and cows; Pirie and Greenhalgh (1977) for steers
Not only are higher levels of NaOH feasible in mixed straw diets, but may even be essential if concentrates constitute an important part of the diet (i.e., more than about 40%). Levy et al. (1977) fed high-concentrate diets (60–70% concentrates and 30–40% straw) to fattening bulls. Straw treated with 4 kg NaOH/100 kg was very little better than untreated straw in terms of animal performance, but the straw treated with 8 kg NaOH was considerably better. Greenhalgh et al. (1976) and Pirie and Greenhalgh (1977) fed sheep and beef cattle on barley-based concentrate diets containing 50–60% concentrates and 40–50% straw. Treatment of the straw resulted in a large increase in organic matter digestibility (18 and 20 units, respectively); intake and weight gain were also improved markedly (table 15). Earlier it was pointed out that such increases should not always be expected with high-concentrate diets (paragraph 23). The success of these experiments appears to be due to the fact that the straw was treated with 8 kg NaOH rather than 4–5 kg. Depressed straw digestibility is caused by a lowering of rumen pH by the rapid fermentation of starch. It can only be supposed that in these experiments the high level of titratable alkalinity (unreacted NaOH) acted decisively to prevent a fall in rumen pH. Rumen fluid pH was not measured in these experiments. Incidentally experience has shown that straw treated with 8 kg NaOH should be fed mixed with the other ingredients in the diet and not separately, as it is somewhat unpalatable.
The use of Ca(OH)2 in treating straw has always been of interest, as already mentioned (paragraph 41), because it is cheaper than other alkalis. With spray-treated material Ca(OH)2 has consistently be found inferior to NaOH (reviews by Jackson, 1977 and Klopfenstein, 1976). Gharib et al. (1975b), however, found that when treated popular bark was ensiled for 150 days Ca(OH)2 was as effective as NaOH. Wilkinson and Gonzalez Santillana (1977) ensiled treated barley straw for 90 days and found Ca(OH)2 2/3rds as effective as NaOH (see also paragraph 75). Coming back to the daily treatment and feeding of straw, mixtures of 1 kg Ca(OH)2 and 3 kg NaOH when used to treat 100 kg straw have been found in several experiments (review by Klopfenstein, 1976) to be superior to 4 kg NaOH in terms of the performance of growing lambs and calves. It is not known whether this is due to the effect of the chemicals on the digestibility of straw or a nutritional effect of the added calcium.
A variation of the simple spray treatment described above is the Boliden method. This method has been developed by a private company in Sweden, Nid Boliden AB of Helsingborg. Straw is sprayed with an alkali solution and then with an acid solution in a specially designed apparatus. The unit seen by the consultant at the Agricultural University of Norway could treat a 500 kg of baled straw per day. A schematic diagram of the apparatus used is given in figure 5. In the morning a fresh batch of baled straw (500 kg) is placed in the treatment chamber on the mesh floor. An NaOH solution sufficient to provide 22.5 kg NaOH (4.5 kg/100 kg straw) is pumped into the funnel under the chamber. The water supply to the funnel is then turned on. As the funnel begins to fill up a pump starts and pumps the solution on to the straw through spray nozzles in a travelling overhead spray boom. The straw becomes saturated in about 1 1/2 hours after which excess solution drains back into the funnel and is recirculated. A float value in the funnel controls the flow of water into the funnel. About 1800 l of solution is made and at equilibrium all but about 100 l is in the saturated straw. A charge of 22.5 kg of Ca(OH)2 is also introduced into the system as a suspension in the water. The treatment solution is circulated for a 4 hours. The saturated straw is then allowed to stand overnight (about 16 hours). Seven l of an acid mixture is then pumped into the funnel and circulation resumed for another 2 hours. The acid mixture is a patented product sold by the company. It contains HC1 and H3PO4. The pH of the straw is brought down to 8–9. A further hour or so is allowed for draining and then the straw can be removed and fed. The apparatus can then be loaded with fresh straw.
Figure 5. Chamber for treatment of straw by the Boliden method (refer to paragraphs 64 and 65).
The treated straw is of course saturated (20% dry-matter approximately) and in this respect resembles wet treated straw. Chemically, however, it resembles dry-treated straw neutralised with mineral acid. It has sufficient calcium and phosphorus to eliminate the need for the usual mineral supplements. The straw is being evaluated at the Agricultural University of Norway and at the moment very little is known about its feeding value. Digestibility in vitro of ‘grab’ samples from untreated and treated bales has been determined; the values are 45 (39–50) for untreated and 68 (65–75) for treated (Sundstφl, private communication-1977). It is not possible to assess the effectiveness of this method from this limited data. Feeding trials will have to be done. It is suggested that such trials aim at distinguishing among the effects of NaOH, Ca(OH)2 and acid. The method should also be compared in a single trial with the simpler daily-treatment method described in the preceeding paragraphs using 4.5 kg NaOH.
Considerable experimentation with ammonia treatment has been done in the last few years. The stacking method in which anhydrous ammonia is used is described in paragraphs 79–83. Development work on the treatment of straw in air-tight tanks has been carried out at the Biotechnical Institute at Kolding (Rexen, 1977; Waagepetersen and Vestergaard Thomsen, 1977). A cylinderical tank which can accomodate 80 bales has been tested. Anhydrous ammonia (3.5 kg) is introduced and circulated by a fan. The tank is insulated to conserve the heat produced by the chemical reaction of the ammonia with the straw, which is considerable. A five-day treatment period has been found to give an increase in enzyme digestibility (of barley straw) of 15 units (27 to 42) which corresponds to an increase in in vitro organic matter digestibility of 14 units (54–68) (B. Rexen, 1977). The average temperature inside the tank during the first 24 hours was 38°. In another trial with the same tank steam was introduced to raise the temperature to an average of 70°. The treatment period lasted only one day. Calculated dry-matter digestibility in vitro increased from 57 to 75. A tank manufactured by a commercial firm in Denmark, which is undergoing testing at the Biotechnical Institute at Kolding, is fitted with electric heating coils to maintain a uniform temperature of 70° for 24 hours since the earlier test showed that, in order to treat one batch effectively every day, this temperature is needed. Something will be said about the feeding of ammonia-treated straw in a later paragraph (81).
A great many digestibility and feeding trials have been carried out with straw treated daily with NaOH and fed directly. The range in increases in digestibility in vitro of published experimental results from some 3 dozen digestibility trials is 0 to 22 percentage units. Different levels of NaOH and different types of test diets were used; in some ad libitum feeding was followed and in others restricted feeding; different types and ages of animals were used; in some cases the treated straw was neutralised; and many more factors could have contributed to this variability. It is, however, desirable, and reasonably possible also, to indicate the expected extent of improvement with ad libitum feeding of strawcontaining diets. These would be 10 units for straw treated with 4–5 kg NaOH/100 kg straw, allowed 24 h ‘curing’ time and fed in diets containing 70–80% or more of straw. This 10 units refers to an increase in derived straw digestibility, calculated by assuming that the digestibility of the other components of the diet are the same for the diets containing treated and untreated straw. In diets containing 40–60% other feeds (concentrates and/or forage), straw treated with 7–9 kg NaOH/100 kg should be expected to increase in digestibility by 17 units if the diets are fed ad libitum and the straw is cured for 24 hours.
|Untreated straw||Treated straw*|
|Dry matter intake, g/kg W0.75||109||109|
|Organic matter digestibility, %||59||67|
|Liveweight gain, kg||0.49||0.64|
|Daily feed cost, Rs./animal||1.70||2.13|
|Feed cost/kg gain, Rs.||3.47||3.33|
|Days to gain 100 kg||204||156|
* Straw spray-treated (farm scale) with 9 kgNaOH/100 kg straw and fed immediately.
Source: Naik and Singh, private communication--1977.
Examples of the results of some production trials with daily treated (NaOH) are given in tables 15–17. An economic analysis of some of these diets is taken up in paragraph 88.
|Untreated straw plus groundnut cake||Treated* straw plus groundnut cake|
|Straw consumption, kg/day||4.5||6.0|
|Concentr. consumption, kg/day||0.8||1.0|
|Total feed costs, Rs./day||0.95||1.39|
|Feed cost/kg gain, Rs.||3.80||3.31|
|Days to gain 100 kg||400||238|
* Straw spray-treated (farm-scale) with 3.3 kg NaOH/100 kgstraw and Ted immediately.
On many farms there may be reasons why the bulk treatment of straw for a whole season or for a month or so is more attractive than daily treatment. If the straw is treated in bulk with NaOH there can be a bonus of enhanced effectiveness of the added alkali. Capital costs of equipment and structures may be higher however.
The Danish farm machines manufactured by Taarup and by J.F. Fabriken produce a treated straw similar to that emerging from the NaOH treater in the industrial process. The bales are shredded, a concentrated NaOH solution (usually 27%) is sprayed on (5 kg NaOH/ 100 kg straw) and then the straw passes through a long mixing chamber in which the straw is squeezed or rubbed between an intricate series of rotating and stationary blades. The penetration of the NaOH is thus facilitated. The treated straw is then blown into a pile. If the pile is big enough (minimum 3–4 tonnes) the treated straw will heat up to a temperature of 80–90°. The heating is caused by the accumulation of the heat liberated by the chemical reactions between the NaOH and the straw. The temperature reaches a peak during the first 3 days and then declines for a further 15 days or so to ambient temperature. As a result of this heating, moisture evaporates leaving the straw dry enough to store if the initial moisture content of the straw does not exceed 17% before treatment. If initial moisture content is more than 17% there will be less heating and insufficient drying leaving a material which will go mouldy or which can heat up again due to bacterial fermentaction; such material appears to behave, in fact, like damp hay. The stack must be made at a place where it is open on at least one side and at the top to ensure adequate drying. Straw treated in this way should not be put in a silo because it will probably overheat and become a fire hazard.
The treated straw is dry, has an attractive golden colour and smells slightly of NaOH. The increases in digestibility resulting from this treatment are shown in table 18. These values were determined by the staff of the Biotechnical Institute, Kolding and they have been supplied to the consultant by Mr. Peder Kjeldsen and Mr. Niels Arne Pedersen of J.F. Fabriken, Sφnderborg. The increase in digestibility in vitro with 5 kg NaOH/100 kg straw is identical to that of factory-treated straw. It is obvious that the heating that occurs in the stack after treatment is vital to this high efficiency. The digestibility increase is not uniform throughout the stack but varies with the extent of temperature rise, which is, of course, most in the centre and less near the surface. The values shown in table 18 are weighted averages. Samples of more than 50 lots of farmer-treated straw have been analysed and have averaged 68% organic matter digestibility in vitro (Kjeldsen and Pederson, private communication--1977).
|Enzyme digestibility, %||Calculated organicmatter digestibility in vitro, %*||Titratable alkalinity,g of NaOH/100 g stras|
|Treated straw on leaving machine||35||62||2.3|
|Treated straw from stack 15 days after treatment||43||69||0.4|
* Calculated using the regression equation :Y = 33.24 + 0.83 X, where Y is organic matterdigestibility in vitro andX is enzyme digestibility(B. Rexen, 1977).
Source: J.F. Fabriken, Sφnderborg, Denmark--1977.
As is the case with factory-treated straw, bulk-treated and stacked straw has rarely been compared with untreated straw in a feeding experiment. One experiment is known to have been done with milking cows (Kristensen, private communication--1977) and one with growing heifers (Andersen, 1977). In the former, straw was fed ad libitum with fixed amounts of molasses (5 kg) and a concentrate mixture (6.4 kg). Treatment increased the intake of straw from 5.5 to 7.6 kg and fat-corrected-milk yield from 20.4 to 22.2 kg. In the latter trial heifers were fed treated barley straw ad libitum and 3 kg other feeds. Straw intake increased from 3.4 to 3.6 kg and weight gain from 0.70 to 0.78 kg/day. Neither of these results is impressive, but the type of diet in which the straw was fed was perhaps not conducive to a larger response from treated straw. The experiment on milking cows is commented upon further in paragraph 82.
The results of several experiments have shown that straw spray-treated with 60–120 1 of NaOH solution and ensiled can be stored for upto one year. There is no microbial fermentation and the straw remains stable due to its high pH. The digestibility does not increase due to ensiling (Wilkinson and Gongalaz Santillana, 1977 b). The temperature of the ensiled mass rises (Wilkinson, private communication--1978), but probably not enough (due to the high water content of the straw) to reach a temperature of about 80 degrees (see table 10) which would increase the effectiveness of the alkali. At ambient or even somewhat higher temperatures, digestibility does not increase after the first 24 h (Braman and Abe, 1977; Gharib et al., 1975a; Gharib et al., 1975b).
|Diet||Dry-matter intake, g||Liveweight gain, g||Feed: gain ratio||Derived organicmatter digestibility, %|
* 70% straw and 30% concentrate supplement
** straw spray-treated with 4 kg NaOH/100 kgstraw
** assuming a constant digestibility of 90%for the concentrate supplement.
Source: Hasimoglu et al., 1969.
Treated, ensiled straw has given very good results in several production trials. On diets containing 70% or more of treated straw liveweight gains of lambs have been increased 4_fold (tables 19 and 20). The results of another feeding experiment with calves (table 21) show how treated and ensiled straw can be used to extend good quality grass silage in rearing calves. Although the treated straw in this case was not as digestible as the grass silage, a diet containing 2/3 rds treated straw still gave weight gains of more than 0.5 kg/day. Klopfenstein (1976) summarised the results of 3 experiments with calves in which maize silage was compared with treated, ensiled maize husks (table 22). The results of these latter two trials as well as those of piatkowski et al. (1974b) (described in paragraph 77) are particularly useful as they indicate the feeding value of treated straw in relation to other roughages silages in this case--and give an indication of how it could be used in conventional high-roughage diets on which young stock is fed. An economic analysis of the data in table 22 has been done by the author and will be presented in paragraph 93.
|Diet||Dry-matter intake, g||Liveweight gain, g||Feed gain ratio|
* Diets contained 25% of a supplement basedon brewers' dried grains and urea
** Straw spray-treated with 3 kg NaOH and 1 kgCa(OH)2/100 kg straw and ensiled
Source: Lamm, 1976.
The ensilling of treated straw seems to offer a possibility of using Ca(OH)2. Many experiments have shown that when Ca(OH)2 is sprayed on straw it has very little effect on digestibility if the straw is fed the same day or the next day (Gharib et al., 1975b; Verma and Jackson, 1975). Gharib et al. (1975 b), however, found it to be as effective as NaOH if the treated material (poplar bark) was ensiled for 150 days. With a 90-day ensilling period Ca(OH)2 was about 2/3rds as effective as NaOH (Wilkinson and Gonsalez Santillana, 1977 a). The advantage of Ca(OH)2 over NaOH is, of course, its lower cost.
A special situation in which the ensilling of treated straw may be useful is in Italy. Paci (1955) reported that rice straw is still green at harvest in the autumn and that there is insufficient sunny weather to dry it. He tried ensilling it with mineral acids with good results. Alkali treatment and ensiling might be a better alternative. All over Europe much straw is rained on before it can be picked up from the field. It could be successfully kept and used as a feed by alkali treating and ensiling.
Piatkowski et al. (1974 b) treated barley straw with 5 kg NaOH/100 kg (100 l solution) and after 2 weeks ensiled it with green maize forage in the following proportions on a dry matter basis: 17:83 and 34:66, respectively. There was a greater acid production from the maize during the subsequent fermentation and the amounts of residual sugars were reduced. The pH values of pure maize silage and the two mixed silages were 3.8, 4.0 and 4.3, respectively. The organic-matter digestibility of the three silages was 69%, indicating that the digestibility of the treated straw was the same as that of the maize. There does not seem to be any advantage of this practice over mixing treated straw with maize silage at the time of feeding. By mixing the treated straw with the fresh maize at the time of ensiling rather than at the time of feeding, the benefit of the treated straw in raising the pH of the diet was not realised; the alkalinity of the straw increased acid production from the sugars in the maize. Thomas and Wilkinson (1975) found that raising the pH of maize silage (from 3.95 to 5.45) by adding sodium bicarbonate increased voluntary consumption by 12%. Thus there would seem to be a definite advantage of mixing treated straw and silage together at the time of feeding.
|Diet *||Dry-matter intake, % of LW||Organic matter digestibility, %||Liveweight gain, kg/day|
(67:33 on a dry-matter basis)
(33:67 on a dry-matter basis)
|SE of means||0.07||0.8||0.04|
* In addition to the silage the calves were fed ureaprills (46% N) and soyabean meal (7.2% N in the drymatter)at the rates of 2.5% of silage/straw drymatter and 0.3% of liveweight,
** Straw was spray-treated with 7.5 kg NaOH/100 kgand ensiled for 76 days.
Source: Wilkinson and Ganzalez Santillana, 1977 b.
A novel approach to treating straw in the silo has been studied by Oji and Mowat (1977). They ensiled maize stover after spraying it with 10 1 of a 50% solution of urea/100 kg. Initial moisture content of the stover was 55%. All the urea was decomposed within 20 days. The ammonia released would presumably react with the stover and increase its digestibility. This possibility should be investigated.
|Maize silage diet**||Treated maize husks diet***|
|Liveweight gain, kg||0.75||0.75|
|Dry-matter intake, kg||7.26||7.17|
* Straw treated ith 3 kg NaOH and 1 kgCa(OH)2/100 kg straw
** 90% maize silage and 10% supplementson a dry-matter basis
*** 80% maize husk and 20% supplements ona dry-matter basis
Source: Klopfenstein, 1977
Ammonia treatment of straw has a strong appeal because of the advantages it has over NaOH treatment. These are: no residual alkali and an increased nitrogen content in the straw. Three ways of applying ammonia have already been described (paragraphs 56, 66 and 78). In the stack treatment method a stack of straw bales 2 m high and 4.5 m square is made in the open on a ground sheet of 0.2 mm polyethylene 10 × 10 m in size (figure 6). The dimensions can vary and these are given as an example; the dimensions for a particular situation will depend upon the amount of straw to be treated and the standard widths of polyethylens sheeting available. In building the stack a 2 × 2 cm lath should be placed in between the 3rd and 4th layers, and 6–8 bales are placed on the top at the centre to give a slope to the plastic cover. The lath will later be pulled out to make a hole in which the ammonia delivery pipe can be inserted. The stack is then covered with a 10 × 10 m top sheet, leaving a free margin of 0.70 cm all around which corresponds to the free edges of the groundsheet. These free edges are then rolled up together on 3 sides as shown in figure 6. The delivery pipe from the anhydrous ammonia tanker is then inserted into the stack and NH3 added at the rate of 3.5 kg kg/100 kg straw. After withdrawing the delivery pipe, the fourth side is quickly closed. In Northern Europe 8 weeks are recommended for treatment during the winter, but in the summer or in warmer climates the maximum increase in digestibility is achieved in less time--only about 4 weeks. The stack must be aerated for a day or so after opening before the straw is fed to animals. The method, as well as the feeding value of the treated straw have been described in detail by Sundstol et al. (1977b); Arnason and Mo (1977) and Kernan et al. (1977). The method could be adopted to stacks of loose straw, long or chopped. Ammonia hydroxide solutions can be used instead of anhydrous ammonia.
A disadvantage of this method of treatment is that NH3 is a weaker base than NaOH and thus the same degree of improvement in digestibility is not possible with NH3 as with NaOH. Digestibility in vitro has been found to increase by a maximum of only 15 percentage units. This maximum occurs at about 3 kg NH3/100 kg straw. Another disadvantage is that about 2/3rds of the ammonia used (when 3.5 kg/100 kg straw applied) remains unreacted. This must be carefully evacuated from treated stacks. If straw is damp, some of this excess ammonia is retained in the straw, making it unplatable. Further, it represents a waste of valuable NH3. It should be possible to devise systems in which this NH3 is recycled and used.
A number of digestibility trials have been done to compare untreated with NH3-treated straw. These have been done with sheep. The increases ranged from 8–17 units. Several feeding experiments have been done and the results are summarised by Arnason and Mo (1977); Sundstol et al. (1977b) and Homb et al. (1977). As with NaOH-treatment of straw, voluntary intake is increased by NH3 treatment, unless, as already mentioned, the straw is damp. An example of the potential of NH3 treatment of straw for improving the weight gain of cattle is given in tables 23 and 24. The data indicate a good response to treatment even in a diet high in concentrates. The results of a trial in which treated straw was no better than untreated have also been reported (Kvale and Homb, 1977); the problem here could conceivable have been inefficient treatment which can easily occur if the plastic sheet gets a hole in it. Several experiments have been done on milking cows. The results of one in which treated and untreated straw were compared are given in table 25. The treatment of the straw resulted in a little increase in milk yield even though concentrate and beet consumption were less on the treated straw diet. In two other experiments (Mo, 1975 and 1976) NH3-treated replaced some of the grass silage in the diets of milking cows. On an average of four comparisons 3 kg of NH3-treated straw plus 1 kg concentrates was found to be equivalent to 3 kg of grass silage dry matter. Calculated net-energy value was less than for the Beckmann-treated straw reported on by Homb et al. (1977) and equivalent to only average-quality silage.
Figure 6. Procedure for the bulkd treatment of straw with NH3 in stacks (refer to paragraph 79).
Source: Sundstφl et al., 1977a.
|Untreated straw diet||Treated straw diet|
|Straw intake, kg**||3.4||4.3|
|Liveweight gain, kg||0.22||0.53|
* Steers weighed 300 kg initially.
** In addition to treated straw ad libitum,the steers were each fed 3 kg grass silageand 2 kg of a concentrate mixture per day.
Source: Pestalozzi and Matre, 1977
In the experiment on milking cows referred to in the preceeding paragraph (see table 25) the treatment of straw was apparently equivalent to only about 1 kg concentrate mixture. Equally poor returns from straw treatment were observed in the experiment of Kristensen, private communication--1977) (paragraph 72). Intake of straw increased due to treatment in these experiments and presumably digestibility also. In the experiment of Greenhalgh et al. (1976) (table 15), cows fed a straw-concentrate diet (50% straw and 50% concentrates) consumed 10.8 kg dry-matter on the untreated straw diet and 13.4 kg on the treated straw diet. They produced 17.6 and 19.0 kg of milk daily. Thus 2.6 kg extra food, containing 1.3 kg concentrate, plus the extra energy resulting from the treatment of all the straw eaten produced only 1.4 kg milk. The same two diets were fed to lambs and weight gains were doubled by straw treatment. The poor showing of treated straw in these experiments was probably because the scale of concentrate feeding was set for untreated straw and thus the animals, already adequately fed, were unable to respond to the improved feeding value of straw by producing more milk. In such experiments, three diets should be compared (paragraph 25). The scale of rationing concentrates should be that appropriate for the conventional roughage. The same scale should also be followed for the treated and untreated straw diets. The value of treated straw and also of treatment could then be determined.
|Untreated straw diet||Treated* straw diet|
|Material composition of diet, %|
|Vitamins and minerals||2.25||2.25|
|Feed consumed, kg/day||5.5||5.9|
|Feed: gain ratio||14.4||11.2|
* Straw treated with 3.5% NH3 for a minimum of 30 days.
The nitrogen bound by straw during NH3 treatment has been shown to be utilised by animals (Mo, 1977).
|Untreated straw diet||Treated straw diet|
|Straw intake, kg DM||6.1||6.9|
|Concentrates, kg DM||9.3||8.8|
|Beet pulp, kg DM||2.0||1.8|
|Milk yield (4% FCM), kg||19.0||19.4|
Source: Rissanen, et al., 1977.
The possibility of biological methods of straw treatment has a great appeal as an alternative to the use of expensive (in terms of money and energy) chemicals. Pollution would also be reduced. It must be remembered, however, that whatever organism is grown on the straw must obtain its energy from the straw itself. Organisms which degrade cellulose and hemicellulose are of no use since they only deplete the straw of nutrients which the ruminant itself can digest even without any treatment. Successful biological treatment must be based upon the use of organism which degrades lignin. While there is no organism that degrades only lignin, there are some, notably the white rot fungi, which degrade more lignin than they do cellulose, thus leaving a residue with a lower percentage of lignin than the original material. Baker et al. (1975) have tested several such strains of white-rot fungi on sawdust. The digestibility of the sawdust in vitro was improved, and the degree of improvement was highly correlated with the degree of lignin removed. Kirk and Moore (1972) found two strains which increased the digestibility in vitro of sawdust from 46 to 74% in a period of 2–3 months. The sawdust lost 20% of its original weight and 50% and 20% of its original lignin and carbohydrates, respectively. These results are certainly encouraging and experiments using these organisms on straw should be taken up. The long treatment periods needed for this treatment would not probably be a disadvantage for treatment of straw on the farm.
Several methods have been developed for producing single-cell protein using straw as an energy source, either directly, by cultivating cellulolytic organisms on it, or indirectly by hydrolysing its polysaccharides chemically or enzymatically and using the resulting monosaccharides to feed yeasts. One group of workers have experimented with growing yeasts on chemically degraded straw and then feeding the degraded straw along with the yeast to cattle (USDA, 1977). The straw is initially pressure-cooked with H2SO4 and later neutralised with NH3, again under pressure. This hydrolyses straw polysaccharides (presumably hemicelluloses) giving some 20% fermentable sugars. Yeasts are then grown on the hydrolysed straw for 35 h. The entire material is then dried with hot air and fed to cattle. It has a crude protein content of 7-10% (presumably N-salts were added when the yeast was cultured). Digestibility is reported to be 47%. Nothing much seems to be accomplished by this elaborate process. Judging by the digestibility value of 47, the availability of straw carbohydrates to the ruminant is not increased. Some inorganic nitrogen is converted to microbial protein which enriches the straw. But the ruminant do that itself if the straw is supplemented with the urea. However, a pilot plant has been built and data on feeding value and comparative feeding costs should be forthcoming.