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The potential nutritive value of natural straw or low quality forage cannot be exploited if the microbes in the animal's rumen do not receive the necessary nutritive elements for its consumption through the supply of minimum amounts of these elements (see Chapter 1). If one is expecting higher production rates from the animal, the necessary nutrients needed for this must be given through the supply of additional or “supplementary” supplements.

This Chapter, assisted by the information that has already been presented in Chapter 1, has the objective to describe the quantities and the nature of supplements which allow the animal to more fully exploit the feed provided in the two broad nutritional situations normally encountered:

These two contrasting situations will be illustrated by concrete examples.

6.1. Recall of basic nutritional principles

6.1.1. Minimum feed supplements: optimising the use of cellulose in the rumen

These constitute the supplements needed to enable the rumen microbes to function well. The basic principals have already been outlined in Chapter 1.

One recalls that firstly, one must provide the rumen microbes with the nutritive elements which they need for self-multiplication and for degradation (cellulolysis) of the carbohydrates from the cell walls of the straw or low quality forage and following this, to ensure all conditions for maintenance of good cellulolysis.

This consists in essentially supplementing:

This subject has formed the basis for numerous studies over previous decades; Table 12 presents an order of magnitude for improvements to the nutritional value of forages which can result from supplementation with non-protein nitrogen.

6.1.2. Supplements to ensure appropriate levels of animal production

The objective of these supplements is to ensure additional supply of nutritional elements to the animal to allow it to develop target performance levels. In fact straw, even when correctly supplemented to cover the rumen's microbe needs, is hardly sufficient to cover more than the animal's basic maintenance requirements.

These supplements will no longer consist only of nitrogenous components. They will also include energy. They will be made up in proportions according to production requirements such that: Substitution phenomena

“Catalytic” supplements (§ 13 and 14) favour the cellulolytic fermentation process and by this, increase the amounts of forage which the animal can voluntarily ingest. However above this minimum supplement level, as the proportion of feed supplements increases one observes negative interactive digestive phenomena between the forage and concentrates (see Table 13) and substitution of forage by the supplement:

Table 12: Effect of feeding a urea supplement on the digestibility of barley straw (Orskov and Grubb, 1978)
UREA (g/day) Digestibility DM(%) Org Mat Digestibility OMD(%) DM intake (kg/day)
0 45.1 45.8 0.42
6 46.0 46.7 0.45
12 47.8 49.0 0.44
18 47.2 48.3 0.46
Table 13: Influence of the amount of supplement on straw digestibility (Dulphy, 1978)
Straw Supplement Crude Protein % DM of ration Org Mat digestibility OMD of the straw
Nature Amount (% of ration)
Wheat straw   15 8.9 46.1
non treated Maize 30 8.8 43.0
    45 8.9 39.5
Wheat straw Soybean cake 7.5 7.1 42.2
non treated Soybean cake 15 10.9 45.8
  Soybean cake + Maize 30 12.2 44.8

Substitution Ratio = decrease in the intake of the forage (kg) / increase in the amount of supplement offered (kg)

For the sake of simplicity, one may say that as soon as the fermentable carbohydrates represent less than 10 to 15 % of the total dry matter of the intake, cellulolysis will be favoured and the intake of forage will increase. In this case the Substitution Ratio will be negative and one may talk of true or “Catalytic” Supplementation.

Over and above this limit, conditions for cellulolysis in the rumen are no longer met and the intake of forage will diminish, the Substitution Ratio then taking on a positive value. It can even rise to a value higher than 1 which implies that adding 1 kg of supplement will reduce the intake of forage by over 1 kg.

The Substitution Ratio is proportional to the quality of the forage offered: around 1.0 for highly ingestible forages with little encumbrance such as young cereal regrowth, and weak (between 0.2 and 0.4) for poorly ingestible forages with high encumbrance such as mediocre quality hay and straw. It also depends upon the amount of supplement added to the ration (these in fact “encumber” the rumen) and on their characteristics. The ratio is high for supplements rich in rapidly fermentable energy due to the drop in pH of the rumen following the rapid production of volatile fatty acids which they cause and which does not favour cellulolysis. Consequences on the nature and the amount of complementary energy

The energy fraction of the supplement should be added in a manner as to only reduce the cellulolytic activity as little as possible. The results of the considerable research on this subject show that the energy supplements should be:

These recommendations are not only valid for natural bulk forages but certainly more so for treated forage. In effect, treatment is aimed at improving the digestibility and intake of poor quality forage. Moreover, there are risk of adding too much or inappropriate supplements which originate on the one hand, from substitution of the treated forage with the supplement (a higher risk than for natural forage due to its higher quality) and on the other hand, from a reduction to the digestibility of the treated forage due to negative effects of associative digestibility. The final result is that the contribution of the treated forage to the digestible elements supplied in the ration will be reduced and that, in the limit, one will have erased any benefit due to treating the forage (see Table 14a).

Table 14a: Examples showing the influence of the amount and nature of supplements on the digestibility of treated straw
Reference Digestibility of the DM(%)
of the straw in the ration of the whole ration
1/Horton, 1978 (Wheat straw)  
NT only 45.5  
T NH3 only 53.3  
increase T-NT 7.8  
NT + 30% of supplement   58.9
T NH3 + 30% of supplement   62.6
increase T-NT   3.7
2/Fahmy and Sundstol, 1984 (Barley straw)  
T NH3 only 53.0 53.0
T NH3 + 70% of pulp 40.0 70.0
T NH3 only + 70% of barley 22.0 65.0

NT = non treated

T = treated Consequences on the nature and the amount of supplementary nitrogen

a/ Degradable proteins and the various forms of non-protein nitrogen (NPN)

These provide the ammonia needed by the cellulolytic flora for making their own substances and must be provided in proportion to the amount of digestible energy in the ration.

It is estimated that a nitrogen content of 1 % (or 6.25 % of crude protein) is enough for rations which contain less than 50 % of digestible energy (which corresponds to natural straw fed on its own). This should be raised to 1.5 % or even 2 % (between about 9 and 12 % of crude protein DM) when the amount of digestible energy is built up either through energy supplements or by treating the straw. This interaction of energy/nitrogen content is well illustrated in Figure 14 (ORSKOV, 1977).

Figure 14

Figure 14: Effect of the concentration of energy in feed on the theoretical amount of feed nitrogen which is needed to satisfy the needs for microbial synthesis in the rumen. The amounts required are shown for three different levels of degradability of the feed nitrogen (Ørskov, 1977).

Put more simply, the objective is to optimise the microbial synthesis (145 g of crude protein per kg of FOM, or roughly, of DOM) which may be achieved when the added PDIN is equal to the added PDIE.

Balancing a ration reverts to equalising the supplies of PDIN and PDIE contained in the different ration constituents.

b/ Supplementary nitrogen for the production needs of the animal, which should be given following the same rules.

Research carried out over recent years has shown that, particularly in the case of low quality forages, it is also useful to supply, in addition to degradable nitrogen, supplementary crude protein in the least degradable form possible (PDIA): oilseed cake, animal protein, vegetable protein rich in tannin such as leguminous shrubs (Leucaena leucocephala, Gliricidia, Sesbania, Acacia, etc.) which further improve the nutritional value. This phenomenon is clearly illustrated in Table 14b.

In effect, these proteins ensure supply of the amino acids which the host animal needs for production purposes (milk, growth, work and reproduction). The full nitrogen needs of most animals in production cannot be covered only by synthesis of the microbial proteins. Consequently, it is preferable to supply small amounts of feed proteins which will escape degradation in the rumen.

These are also useful to the rumen's microbes which can beneficially use the amino acids and short chained polypeptides through synergy. This discovery, which is relatively recent (RAMIHONE, 1987; RAMIHONE et al., 1988; SILVA et al., 1989) is still rarely taken into consideration. It is illustrated in Table 14b which shows the beneficial effect of protein sources which are of low degradability on the cellulolytic activity in the rumen. One should also mention the observations of OOSTING (1993) which show the synergetic effect of potato proteins which have little degradability; these improve the yield of the microbial synthesis (PDIM) and at the same time supply amino acids to the intestine (PDIA, nitrogen of low degradability or “by-pass” N). It should also be noted that certain protein supplements, such as fish meal, also supply fatty acids with branched chains which are indispensable for the microbial synthesis and to the host animal

Table 14b: Effect of fish meal (FM) (50 g/kg of straw) and beet pulp (BP) (150 g/kg of straw) on the intake and digestibility of straw either supplemented with urea or treated with ammonia (Silva et al., 1989)
Non treated + urea - 414 49
Non treated + urea FM 480 56
Non treated + urea BP 505 57
Non treated + urea FM + BP 480 59
Treated - 729 57
Treated FM 690 59
Treated BP 717 59
Treated FM + BP 658 64

And finally to mention an important point presented in the 1960's (EGAN, 1965) and again more recently (PRESTON and LENG, 1980) referring to tropical forages of mediocre quality, in the case of poor nutritional condition of the animals following insufficient absorption of amino acids in the intestine, this can limit the intake of these low quality forages. Only supplying non protein nitrogen will not enable high levels of intake and by that, high performance. Provision of “protected” proteins will stimulate the appetite of the host animal and consequently, the intake of poor forage such as straw. The case of treated forages

Treating certainly improves the nitrogen content and microbial synthesis of the forages (see Chapter 5) but not in such significant quantities as might be theoretically expected (importance of the indigestible portion (“MAND” in French) of the crude protein supplied through treating). Research results point to the advantages of a supplement of poorly degradable proteins when this is added to treated forages (see Tables 15a and 15b).

Table 15a: Effect of the nature of the nitrogen supplement in ammonia treated straw on the growth rate of Pie Noire Friesian heifers (supplements of identical PDI designed for a growth rate of 350 g/day) (Chenost and Besle, 1993)
Nitrogen supplement Fish meal Urea Rapeseed cake Soybean cake Fish meal
DM intake (kg/day)          
Straw 5.07 6.82 7.09 6.90 6.80
Pulp (*) 3.10 2.40 1.95 2.20 2.30
Nitrogen supplement 0.49   0.66 0.35 0.27
Urea 0.10 0.09      
Minerals and vitamins 0.10 0.10 0.10 0.10 0.10
Average Daily Gain (ADG) (g/day) 347 266 392 381 431

(*): dehydrated beet pulp

Table 15b: Effect of a supplement of fish meal on the digestibility of DM of urea treated rice straw and on animal performances (Saadullah et al., 1982)
DIET 1 2 3 4
Treated rice straw (kg/day) 2.6 2.3 2.3 2.4
Water hyacinth (kg/day) 0.2 0.1 0.1 0.1
Fish meal (kg/day) 0.0 0.1 0.2 0.3
Digestibility DM (%) 50 57 60 62
Average Daily Gain (g/day) 57 198 205 192

A trial conducted on two year old Friesian calves (CHENOST et al., 1993) well illustrates all these previous points (see Table 15a); they were given either treated or untreated straw, supplemented by beet pulp and, for the treated straw, a nitrogen supplement of variable degradability (ranging from urea to fish meal); in each case these rations covered the theoretical PDI needs according to a target growth rate of 350 g/day. The trial illustrated everything previously mentioned:

In this respect, it is important to emphasise that this growth response, going even beyond expectations (of 350 g/day), reflects:

One should note that these supplements were not exclusively nitrogenous. They also supplied energy in amounts which are not negligible. This is important to take into consideration in view of balancing the rations (so that PDIN = PDIE).

In conclusion, the nutritional value of poor forages is improved through the addition of non protein nitrogen (urea) which exerts a positive effect on both their digestibility and intake. However, there is reason to be very cautious concerning the amount and the quality of energy supplements supplied. Taken together with the contribution of the straw in supplying the required nutritional elements, response to supplementation will be completely dependant upon this latter aspect. Furthermore, energy supplements should remain within certain limits (from 30 to 50 % of the ration) so as not to change the action of cellulolysis. This is particularly important in the case of treated forage if one wishes to conserve the nutritional (and economic) benefits of treating.

Beyond these limits, it is important to test and to establish response curves for supplements to treated forages, as has been observed by some authors on the basis of research experiments and large scale field trials (DOYLE, DEVENDRA et al., 1986; SCHIERE and IBRAHIM, 1989; DOLBERG, 1993). Observations recorded in China present examples of the growth response of cattle to increasing amounts of cotton cake supplied as the only supplement to straw treated with urea (DOLBERG and FINLAYSON, 1995)

6.2. Practical applications

Having already recalled a summary of the nutritional principals involved, this section focuses on a series of concrete examples gleaned from field experience and which are offered for the benefit of field technicians. They show how to reason the calculation of supplements for low quality forages based on the above fundamental principles, calling upon locally available forage resources as much as possible and only upon minimum needs for imported feed or concentrates which do not always conform to these principles.

Because forage conditions worldwide are so diverse, it is not possible to review them all. Emphasis will therefore be placed on the example of multinutrient blocks, together with a representative selection of cases illustrating the use of locally available resources.

6.2.1. Supplements consisting only of urea

This type of supplement, which may be justified if the calculated quantities of urea needed (see § 1322) in function of the amount of energy ingested from non-treated straw is respected, is sometimes used in the Sahel where there is no support supplements for urea such as molasses. The main idea is to supply the urea to the animal through a water based solution (obviously not given directly to drink, as this would be too dangerous), arranged by spraying it onto the forage before placement in the feed trough.

Setbacks have however already been observed, even in experiment stations, and this technique can only be placed in the hands of the livestock farmer after taking many precautions. The problems lie in the risks of untimely and/or too rapid ingestion of the urea solution. Risks of overdosage are high, as are risks of confusion between the urea solution and the drinking water, … And so in the end, even if elementary precautions can allow avoiding these gross errors, always there are likely to remain problems of properly mastering how to progressively administer the urea solution. All it needs in fact, is a single badly administered impregnation of the solution, allowing it to drain progressively to the bottom of the feed trough and that the animal drink it in a single “gulp”.

The following table presents the recommended amounts of urea for feeding to sheep and cattle which consume “classic” straw with a crude protein content of 3 % DM and with a 40 % digestibility. The quantities have been calculated on the same basis as those given above (see § 1322).

Animal Live weight (kg) Straw intake (kg/day) Amount of urea (g/day)
sheep 30 0.7 – 1.0 11 – 15
cattle 250(1 TLU) 3.0 – 4.0 45 – 60

6.2.2. Mixtures of molasses and urea

This is a procedure which has been well tested for many years.

The principle is to mix urea and molasses together, adding water according to the viscosity of the molasses (the Brix, closely related to the sugar content). The essential element consists in ensuring regular and continuous ingestion of small quantities of this mixture by the animal. For example: spraying the solution onto the low quality forage ration in the feed trough (straw, maize or sorghum stalks, …); the system of licking wheels which dip into a trough of molasses whereby the liquid surface is not accessible to the animal; adding substances (lignosulphates, …) which are bitter or of a dissuasive taste, so allowing reduction of the “palatability” of the mixture and thus, the amount and speed of intake, etc.

By spreading out the intake of the ration as uniformly as possible, this allows;

These mixes are strongly recommended as they include the minerals and vitamins needed for cellulolysis and for the basic animal requirements.

There are many practical examples available concerning such usage. The most appropriate to cite here are those practised in Egypt and Tanzania.

Egypt disposes of two sugar refineries in the Nile Valley and many livestock farmers base their production on “berseem” (Trifolium alexandrinum) in winter and rice straw in summer. It was decided in the 1980's, through an FAO/UNDP and later an EU project concerning improvement of animal feed, to create a plant for the manufacture of a molasses/urea mix (MUFeed) near to Alexandria at Noubariya. This production unit, operating since 1983, now has a capacity of 45 ton/day of the liquid mix and 6 ton/day of the solid mix sold as blocks. These products are commercialised to the livestock farmers on the delta who may, in addition, also take advantage of the various services offered through a number of ammonia treatment centres for straw. The composition of the liquid mix is as presented in the following table:

Formula of the liquid mix molasses/urea (MUFeed) commercialised in Egypt:

molasses 91.36
urea 2.50
mineral mix 1.14
water 5.00

The mineral mix contains 14.6 % P; 5.0 % Mg; 6.6 % S; vitamin A, 230,000 IU/kg (where IU are International Units); vitamin D, 46,000 IU/kg; vitamin E, 1,270 ppm; Fe, 3,700 ppm; Zn, 3,000 ppm; Mn, 2,500 ppm; Cu, 630 ppm; Co, 60 ppm; I, 200 ppm.

(Barker TJ et al., 1987)

Tanzania launched a similar but more modest project in 1983/84 under the FAO Project “Development of milk production for small farmers in the region of Kilimanjaro/Arusha”, a region of coffee and banana production.

Advantage could be taken of the proximity of the sugar industry on the Masai plain. It comprises the programme known as MMU (Mixture of Molasses and Urea) developed around a cooperative mixing centre and with a distribution and storage network for the mixture established amongst the rural cooperatives of the region.

The mixture contains 3 % of urea. It is distributed by spraying the forage in the feed trough on the basis of a daily ration recommended to the dairy farmers of 0.5 kg/day/100 kg liveweight. The forage consists of banana leaves, grass chopped along the roads and, during the dry season, stalks from maize cultivated on the plain.

They raise Tanzanian Zebu Shorthorn with a liveweight of between 250 and 300 kg but production levels were low (5 to 6 litres of milk/day in addition to that for suckling the calves). The results of a survey conducted amongst farmers using the new technology showed an improvement to milk production averaging 0.5 litres of milk per kg of MMU fed (LAURENT and CENTRES, 1990).

6.2.3. A special case: using multinutrient blocks as a supplement Objective

The distribution of liquid supplements based on molasses and urea for animals held in stables or on ranches, is not well adapted to the needs of small livestock farmers due to transport problems and difficulties in preparing the mixes. Classic supplements are rarely available to these farmers due both to lack of local availability and cash shortages. Using urea as the only type of feed supplement for low quality forages runs the occasional risk of causing food poisoning of the animals.

The new generation of feed supplements for ruminants in developing countries constitute an innovative approach based on the manufacture and distribution of multinutrient blocks supplying the necessary nutrients so as to take maximum advantage of locally available poor quality forages. Originally developed in Australia for rangeland animals (BEAMES, 1963), it was taken up by several authors anxious to spread the idea to developing countries (LENG, 1984; SUDANA, 1985; KUNJU, 1986; SANSOUCY, 1986 and 1995; SANSOUCY et al., 1988). It has formed the focal point for numerous development projects launched by the Forage Resources Group of FAO in many countries (see Appendix 7).

The objective of the manufacture and use of these multinutrient blocks is to make up an appropriate mixture containing urea and local byproducts so as to better maintain the ruminants through the dry season by improving utilisation of coarse forages and low quality pastures. The main advantages of the multinutrient blocks are as follows: Principles for manufacturing the ingredients

a - Principles

The principles consist in making a mixture which, after drying, will maintain a structure which is sufficiently coherent to be transported without damage and yet which can be slowly and slightly “broken down” when licked by the animal.

Several different formulae have been developed (see Table 16). There is no standard formula, rather several which have been adapted to meet the needs of each situation according to availability, price and the nutritional characteristics of the locally available raw materials and byproducts. The physical/chemical characteristics of certain constituents such as molasses and cereal bran vary greatly from one country to another. Their use in a given proportion may also not necessarily lead to the same results. It is therefore advisable to first conduct a series of control tests before recommending a particular formula to farmers.

b - Characteristics of the ingredients

Whatever may be the formula adopted, common ingredients in a block are as follows:

- urea:

this consists of the fertilizer, urea (46 N). Its concentration is generally limited to 10 % in order to avoid any risk of causing poisoning. It is the main constituent from the nutritional point of view.

- fibrous feed:

the main purpose of this is to absorb the moisture of the block and to give it good structural quality. The most commonly used ingredient is cereal bran (from wheat, rice, sorghum, millet or maize). Apart from being a good absorbent material, bran (particularly wheat bran) supplies nitrogen, energy (starch) and phosphorous in a form which may be assimilated by the animal. Other products such as finely milled shells from groundnut, finely milled straw, fine bagasse, finely ground dried leaves from leguminous shrubs (Leucaena spp,…), can each either partially or totally replace the cereal bran.

- minerals:

salt supplies sodium chloride (NaCl) which also helps to consolidate the blocks and control the rate of their ingestion. Ordinary cooking salt is often used. Crude salt, salt blocks or natural sodium carbonate (natron) which are traditional in certain countries, can also be incorporated into the mix. Quantities added are normally in the range of 5 to 10 %. In some countries where the humidity can rise above 60 % during the rainy season, it is recommended to limit the addition of salt to 5 %.

Calcium carbonate, di-calcium phosphate and bone meal enrich the blocks in P and Ca. If these are not locally available and/or their cost is prohibitive, they may be replaced by lime and superphosphates. The mineral composition of these constituents is given in Table 17.

- molasses:

these are an excellent source of fermentable energy, which optimise the use of the urea, and of minerals, particularly the trace elements; they help generate appetite due to their sugar content. Molasses should not be diluted as their consistency is an important factor in successful fabrication of the block. When large numbers of blocks are being made the recommended Brix should be at least 75 (this is related to the sugar concentration of the molasses which determines their dry matter content). Molasses content should not be higher than 40 to 50 % as too much will reduce the hardness of the block and lengthen the drying time required (even more so when the ambient humidity is high).

Table 17: Calcium and phosphorous content of some mineral sources which may be incorporated into the multinutrient blocks (%)
Sources Calcium Phosphorus
Calcium carbonate 33–38 0
Di-calcium phosphate 23–24 16–18
Natural tri-calcium phosphate 20–34 10–17
Bone meal 25–27 12–13
Super triple phosphate (0-46-0) 16 20
Simple super phosphate (0–16.5-0) 20 7

Even though it is preferable to use molasses for the above mentioned reasons, it is not obligatory and countries where they are not available can make blocks without any molasses, as has been demonstrated by HASSOUN and BA (1990).

- bonding agents:

cement, such as used in the building trade. Mixing in about 10 % is generally sufficient and it is not recommended to add more than 15 %. If the price is high, quantities can be dropped to 5 % and it should then be used in association with clay. A dosage within these ranges presents no danger to the animal (the amounts which are actually ingested are, in any case, very small). Cement which is old or has been badly stored is likely to cause problems concerning cohesion of the block.

quicklime, which comes in the form of a rock and gives off heat in the presence of water. This must be ground before use. Slaked lime in powder form is easier to handle but has not always given such good results. Quicklime used as the only bonding agent gives results comparable to those of cement when it is mixed in a proportion of 10 % but the blocks are slightly less hard. Lime has the advantage of supplying calcium and reducing the drying time for the blocks.

clay, such as used in brick making and by artisanal pottery industries. Use of clay is comparatively recent but has given very satisfying results (through the projects FAO/TCP/Cambodia/2254, KAYOULI, 1994 b and FAO/TCP/Tanzania/2255, PRESTON, 1993). The combined use of clay (20 %) and cement or quicklime (5 to 10 %) considerably improves block hardness and reduces their drying time as compared to cement or quicklime being used alone. Locally available clay represents an interesting alternative for reducing the production costs of the blocks.

- other ingredients:

Other byproducts can also be incorporated into the blocks. These include olive cakes (in North Africa and the Near East), dried poultry litter, animal meal (from fish or slaughter house waste), cake from cotton seed, groundnut, sesame, flour from lucerne, marine algae, barley residues from breweries, … And finally the blocks can be enriched with trace elements, particularly if they do not contain molasses and in regions where trace elements are strongly lacking or for animals with special needs for them. Phosphorous sources such as di-calcium or mono-calcium phosphate may be added in quantities of up to about 5 %. Fabrication methods

The fabrication technique is simple and has the advantage of being able to be undertaken with a minimum amount of equipment which is accessible to the small farmer. It is fully described in Appendix 4 where two alternative formulae are described which have been used in two separate development projects, one in Cambodia (FAO-TCP/Cambodia/2254, “Plan for safeguarding cattle”) and the other in Niger (FAO-PNUD/NER/89/016, “Extension of the method of urea treatment”).

6.2.4. Supplements with green forages and crop residues

It is equally possible to supplement straw with other richer forages. These include:

This form of supplement, although often advocated as being nutritionally justified and beneficial (PRESTON and LENG, 1984; DEVENDRA, 1991; PRESTON, 1995), is generally underestimated and under-used. It is true that it does not always lend itself to regions with a marked dry season, rather to mixed farming systems of crop and livestock production in the humid tropics.

Forage supplements are numerous and very diverse. They include green grass mown or pastured along roadsides, access roads and dikes in riceland areas, leaves from bush legumes used as fences or enclosures (Acacia spp., Erythrina spp., Gliricidia spp., Leucaena leucocephala, Sesbania spp.,…), leaves and hay from leguminous crops such as cassava (Maniholt esculenta), Pigeon peas (Cajanus cajan), etc…

Leguminous shrubs present special interest, compared to the more classic forage resources, as they last and continue to be available during the dry season. They are now the subject of intensive research and development on a scale much larger than previously was the case (SPEEDY and PUGLIESE, 1992). Currently, one of the main objectives is to integrate them better into agricultural production systems such as in Asia.

Table 18, which presents results from a number of trials in Asia, well illustrates the interest in supplementing straw with leaves of a legume grass (Stylosanthes verano) or a bush legume (Gliricidia spp). Very little substitution of the straw by the green forage was observed, indeed the intake of straw increased as amounts of forage were increased in the ration, so increasing digestibility; net results showed a weight gain of the animals (calves) which rose from negative to positive values.

Table 18: Effect of supplementing rice straw, either non treated (NT) or urea treated (T), with legume grass or shrubs on intake, digestibility and growth rates
(1) and (2) Straw utilization Project (1986)
(3) Suriyajantratong and Willaipon (1985)
  1 2 3 4
(1) Bullocks (98–109 kg)        
DM intake (kg DM / 100 kg Liveweight)        
Rice straw (NT) 2,7 2,8 2,5 2,2
Gliricidia   0,3 0,6 1,1
Digestibility DM (%) 47 46 49 55
ADG (g/day) -113 -54 -94 10
(2) Bullocks (98–109kg)        
DM ingested (kg DM / 100 kg Liveweight)        
Rice straw (T) 3,2 3,1 3,4 2,8
Gliricidia   0,3 0,5 1,0
DM Digestibility (%) 41 45 50 52
ADG (g/day) -28 63 134 130
(3) Calves (140–150kg)        
DM ingested (kg DM / 100 Liveweight)        
Rice straw (NT) 3,02 3,21 3,22 3,37
Verano Stylo   0,44 0,96 1,36
ADG (g/day) -165 11 60 104

This type of supplement favours celluloysis due to the presence of digestible cell matter (the leaves). It supplies additional digestible organic matter as well as crude protein (contained in the leaves) which are generally lacking for good digestive utilisation of poor quality forages. It allows the nutritional state of the animal to progress from one of subsistence to maintenance or even that of modest production.

The leaves, hay and stalks from food crops are widely used in the agro-pastoral sudano and sudano-sahelian regions of Africa where hay from groundnut and cowpea are usually carefully collected and stored after the harvest and even form the basis for significant trading activities. A similar situation occurs in North Africa with hay from peas, chickpea, vetch, …

In a similar manner to that of the forage supplements described above, these crop residues, which are more digestible and richer in crude protein than the straw which they supplement, have the same “catalytic” effect on the digestive utilisation of the straw and thus generally improve both the digestibility and intake, as well illustrated in Table 19.

The interest in these supplements is that generally, their cost only involves their collection from the field.

6.2.5. Supplements using local byproducts

The objective here is to supply supplements of energy and nitrogen so as to cover the production needs of the animal.

These supplements must not only respect the nutritional aspects described above, but also: Supplements available “on the farm”

This source of supplements should be mentioned as it places no reliance on products available in the market, rather only upon those feed sources directly available at farm level.

Table 19: Influence of supplementing natural barley straw with pea and vetch hay on the organic matter digestibility (OMD) and on the intake of dry matter (DM) and digestible organic matter (DOMI) of sheep. Comparison with cottonseed cake
Supplement (% of the DM of the ration) DM intake (g/day) OMD (%) DOMI (g/day)
None 785 46 360
Pea hay      
(33 %) 955 48 455
(67 %) 1070 46 490
Vetch hay      
(33 %) 1065 48 515
(67 %) 1345 50 670
Cottonseed cake      
(15 %) 1250 49 615

source: Goodchild et al., 1992

These food sources are generally not numerous and can be quickly listed. They mainly comprise products originating from cereals produced on the farm and processed locally (grain fragments and bran from rice, sorghum, millet, maize, …) or brought in but locally processed products (mainly wheat) together with cotton seed. As far as other byproducts are concerned such as cake, these are generally exported or, if there is a surplus, are only accessible close to the towns and are mainly used by the mono-gastrics after having been passed through the chain of industries producing livestock feed. A similar situation exists for fish and meat meal. Barley residues from the breweries (brewer's grain) are more difficult to transport and are used generally by livestock farmers situated close to urban areas.

Supplements which may be qualified as “strategic” from a nutritional point of view, include the following:

However, as these supplements are often expensive, they are more profitably justified when used as feed for mono-gastrics.

Appendix 6 summarizes the nutritional characteristics of these principal feed resources. “Complete” rations designed to fully exploit the usage potential of low quality forages

Although this is not strictly a technique for supplementation, it could be of interest to mention some of the types of rations which have been tested in the Near East (Project UNDP/FAO Syria, HADJIPANAYIOTOU et al., 1989) and in Tunisia (KAYOULI et al.; 1993).

Low quality forages (straw and/or maize stalks) constitute the “support” for an association with locally available products, even green forage, which are either mixed in with the feed in the trough or added, layer by layer, as silage is being made. The poor quality forage thus forms the fibrous base for the ration, at the same time raising the dry matter content of the mix which helps to ensure optimum conditions for the process of making silage and for functions of the rumen. Examples of such rations and silage mixes are given in Table 20. They are well adapted for fattening of sheep and cattle.

Apart from the fibrous component of straw, the other elements which generally make up these rations include:

6.2.6. “Classic” supplementation using commercially available concentrates

This subject concerning commercially available concentrates will not be further developed here for the following reasons:

6.3. Conclusion

The ultimate objective for adding supplements to low quality forages is to ease their digestive utilisation and to increase their intake. This may only be achieved by optimising the process of cellulolysis in the rumen.

The minimum supplement, called “catalytic” by the authors, aims precisely to favour this cellulolysis by supplying the rumen's microbes with those elements which are lacking in the forage. These are composed of nitrogen supply (degradable or non protein, such as urea), minerals and the vitamins A and D3.

The typical example of such a supplement is the multinutrient block. Experiences and practical examples in this domain are both numerous and encouraging. This supplement allows changing the nutritional condition of the animal from one of deficit to that of subsistence or maintenance.

In order to progress to a nutritional condition of production, additional feed is required together with production supplements. However these supplements must not adversely affect the process of cellulolysis. They should thus be nutritionally compatible with good cellulolysis. This principle is equally applicable to fresh and to treated forages. It is convenient to pay particular attention to the quantity and quality of these supplements, specially in the case of treated forages, if one is to avoid losing the benefits of treating and so “treating for nothing”.

Strategic supplements are those based on cereals, grain which are rich in protein and oil seeds (or cake based on any of these), the leaves and pods from bushes and forage legumes and above all, meat and fish waste or meal. These should not be considered to mean commercial concentrates which are not normally designed for such circumstances.

The results in terms of animal production, will be examined in the next Chapter which brings together results from trials and field experiences which concern the use of fresh and/or treated forages.

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