SESSION II (contd.)

PROCEDURES FOR RESEARCH INTO THE TREATMENT OF CROP RESIDUES AND AGRO-INDUSTRIAL BY-PRODUCTS IN DEVELOPING COUNTRIES

Frik Sundstol

Department of Animal Nutrition
Agricultural University of Norway
1432 As-NLH Norway

SUMMARY

It is not possible to describe procedures for research into treatment of agro-industrial by-products and crop residues that will fit under all circumstances. Some view-points of general character are outlined.

Before starting a research project on this topic, a feasibility study should be carried out to identify some of the relevant problems and to establish the right approach. Information that could be of interest in such a study might include:

• Amounts, quality and distribution of materials
• Alternative uses of the materials
• Alternative feeds and feed supplements
• Level of technology in the agricultural sector
• otential improvement due to treatment
• Availability and cost of chemicals and equipment
• Adverse effects of chemicals
• Possibility of government support

A research programme on crop residues and agro-industrial by-products may be carried out at three levels: (i) basic research, (ii) applied research and (iii) field research. These are equally important and should run more or less parallel.

Basic research should be carried out on university or experimental farms where fundamental problems are studied. Field research should be carried out at well-run private farms, government farms or the like. Here practical aspects of by-product utilization should be studied and the “bottlenecks” of the technology uncovered.

Sound training of the personnel employed is vital for a successful project and action should be taken to ensure a rapid flow of information between the various groups working in the field of by-products.

It is difficult to recommend one particular method for treatment because this will depend on the local conditions. For many tropical countries, it might be logical to think of ammoniation by urea treatment as the first alternative.

INTRODUCTION

Crop residues and agro-industrial by-products include a great number of materials of which straw of cereals, stover from maize and sorghum, maize cobs and bagasse are among those of greatest importance quantitatively. For more detailed information, see Kossila (1984). This paper deals mainly with straw and other fibrous by-products, but some of the points made will have relevance also for other by-products.

The extent to which these residues are utilized as animal feed varies a great deal. In some densely populated areas almost 100% of the straw and other residues are utilized as feed whereas in other areas these residues are largely underutilized, i.e. burnt in the field. Even if a crop residue is used 100% as feed, the nutritive value may be improved by treatment in one way or another. Experiments have shown that it is virtually possible to double the nutritive value of straw by chemical treatment. This means that the net energy content of treated straw may be as high as that of early cut grass or grass silage. This shows the potential of treatment even if this type of treatment (wet NaOH) is not applicable everywhere.

There are a number of methods developed for treatment of fibrous by-products and some of these are listed in Table 1.

TABLE 1 Methods for treatment of straw and other fibrous by-products (see Sundstol and Owen 1984)

Of these, only a few may be of interest for developing countries at present.

To establish procedures for research into the treatment of crop residues and agro-industrial by-products in developing countries seems to be an extremely difficult task. The main reason being that conditions in the developing world vary so much from South East Asia to Africa to Latin America. Even within these regions extremes are found as to farming conditions, level of technology, infrastructure, economy and political system. These factors may have a fundamental influence on the strategy that should be chosen in an attempt to improve the utilization of crop residues and agro-industrial by-products.

I shall not attempt to describe procedures which work under all circumstances, but rather to point out important elements in a strategy for improvement of the nutritive value of fibrous by-products.

FEASIBILITY STUDY

According to Jackson (1981), the livestock productivity in the tropics has not, in general, increased during the last 30 years, mainly because inappropriate technology has been promoted. Even if the explanation is not as simple as that, it is an extremely important statement to bear in mind for those who are involved in work on low quality roughage utilization in developing countries.

Therefore no research programme on treatment of low quality roughages should be launched before a feasibility study has been carried out. The study need not be very comprehensive, but it should make the planners think thoroughly through some questions that ought to be clarified before starting on a research programme. Before this is done, it is difficult to decide where to start and where to go.

Amounts, quality and distribution of materials

This is a logical point to start at because the quantities of crop residues and agro-industrial by-products will determine the attention that should be given to them as a potential source of feed. The possibility for building up a country-wide system for treatment will also depend on the actual amount available and its distribution. If grain production is located far from animal production, the possibility of utilizing the straw as animal feed is greatly reduced. The transport cost of the straw may simply be prohibitive. Screening tests may be carried out to get valuable information about the degradability of the various materials. This is important in order to judge what sort of treatment or supplementation would be most suitable to improve its feeding value.

Alternative uses of the materials

Several of the crop residues and by-products available today are used commercially for purposes other than feeding. Examples are sugarcane bagasse used as fuel, straw used as mulch, bedding, fuel, building material or in the chemical industry.

One of the most common uses of straw is of course, to plough it under to improve the organic matter content of the soil. This type of disposal has clear advantages and disadvantages which shall not be discussed further here.

It is likely that technical developments will appear in the future which will make straw, bagasse, maize cobs etc. more attractive raw materials for industrial production. Such uses should be encouraged in areas where the crop residues and by-products cannot be utilized for animal feeding without long and expensive transportation.

Alternative feeds and feed supplements

It seems obvious that the incentive to treat crop residues and agro-industrial by-products is less in areas where high quality forages and concentrate feeds of low cost are abundant (e.g. New Zealand, USA and Sweden) than in countries where feed alternatives to straw are scarce (e.g. India, Bangladesh and Egypt).

It may be argued that if by-products could replace part or most of the grass products in the diet, more land would be available for production of human food. In many countries where this would apply, the market for human products is saturated and the world market prices do not pay for the extra work.

One interesting aspect of this question is the energy cost for production of various forages. Studies in Norway have shown that the expenditure of commercial energy (fuel, chemical energy, electricity etc.) per unit of metabolizable energy (ME) is much lower for ammonia treated straw than for grass silage, hay and other forages (Table 2).

The role of treated by-products in high concentrate diets is a matter of dispute. Because of the fermentation taking place in the rumen of animals fed such diets (low pH) the cellulolytic activity is greatly reduced. This is particularly severe if the materials are finely chopped or ground. Then the rate of passage is high and the time allowed for microbial degradation of the roughages becomes limiting. Kristensen (1984), in reviewing the use of straw and other fibrous by-products in practical diets for cattle concludes that “ground straw is unsuitable in the diet of dairy cows”.

This point may not be so relevant in developing countries where straw and other by-products are fed in long form or coarsely chopped, and where the amounts of concentrates used normally are negligible. But, the point is worth noting particularly in situations where molasses and other readily fermentable carbohydrates are fed.

In most instances crop residues and agro-industrial by-products need to be supplemented with protein, minerals, etc. to ensure an optimal utilization of the diet. These supplements should be available at a price that is not prohibitive for the small farmer. In many cases, urea is an interesing alternative to protein supplementation. On the other hand, catalytic supplements of undegradable protein to urea-treated straw may have a remarkably good effect (Davis et al 1983).

Level of technology in the agricultural sector

Before initiating research into the treatment of crop residues and agro-industrial by-products, an evaluation of what is appropriate technology should be undertaken. What is appropriate may vary from one country to another. According to El Naga (this proceedings) mobile straw treatment machines would be appropriate in Egypt. Parra and Escobar (this proceedings) have described how sugar cane pith is treated with NaOH in Cuba. For other countries treatment with NaOH would be totally out of the question.

Research on oven treatment of straw with ammonia in a country where most of the small farmers are illiterate, would be an example of a completely wrong approach. The importance of advocating a technology that fits into the farming system and helps the farmer to get more out of his crop residues by simple means can never be over emphasized. The research in this area should primarily be devoted to problems the small-holders are facing.

Research for the benefit of the feed mills and the feed industry should be given second priority. Firstly, because information obtained elsewhere may be adopted more directly here. Secondly, because the economy is generally better for the feed industry than for the small-holder in the countryside.

Another point is that when treated on the farm the transport costs are minimized. On the other hand, training of each individual farmer in a treatment method is a much greater task than training the technical personnel from the feed mills. The risk of accidents and false treatment is also greater when the farmers have to do the treatment themselves. Accidents that may occur are: explosion of anhydrous ammonia, burning of eyes and skin by caustic soda and poisoning of animals with urea.

Potential improvement due to treatment.

As already mentioned, it is possible to double the nutritive value of straw by alkali treatment (Dip treatment). Ideally we may say that we choose the method that gives us the greatest improvement. There are, however, many other factors that ought to be considered before choosing one or two methods to be tested. This will not be discussed further here. Worth mentioning is that a ration of urea-treated rice straw plus 0.2 kg protein supplement and 0.2 kg green fodder has given a growth rate of 200 – 300 g/d for a 50 kg calf in Bangladesh (Jackson 1981). A similar diet gave 5 litres of milk per day. These performances are 2–3 times higher than the present averages in the country. Studies in Norway showed that 400 kg steers gained 400 g/d for over 5 months on a diet of ammonia-treated straw plus 250 g of a concentrate mixture, minerals and vitamins (Sundstol and Matre 1982).

Studies by Mwakatundu and Owen (1974) showed that the improvement in digestibility by NaOH-treatment was greater for materials with an initially low digestibility than for materials with a high digestibility. This does not necessarily imply that highly lignified materials become highly digestible after chemical treatment. Experiments with rape straw, bagasse, cotton stalk and rice brans indicate that such materials will have low digestibility even after chemical treatment. It may also be that weak alkalis such as Ca(OH)2 or ammonia are unable to improve the digestibility whereas wet treatment with NaOH gives a satisfactory improvement in digestibility.

Table 3 shows the in vitro, in sacco and in vivo digestibility of barley straw treated according to various methods. It also shows the time taken for half the material to be degraded in the rumen. In the digestibility experiments with sheep (in vivo) 75 g of herring meal was added as a protein supplement and the digestibility of the straw was calculated by difference. The results clearly show that when sufficient protein is provided, there is no improvement in the digestibility by adding urea to the diet. Urea and urine treatment for 8 weeks (ensiling) improved the digestibility of the straw, particularly when a small amount of soybean meal as a source of urease was added. Treatment of straw with anhydrous ammonia (stack) or sodium hydroxide (dry treatment) increased the in vivo digestibility by 14–16 per cent units. The effect of aqueous ammonia (stack) and oven treatment with anhydrous ammonia was slightly less in these experiments. Highest digestibility was obtained for wet treatment of straw which improved the DM digestibility by 20– 25 per cent units.

a In vitro dry matter digestibility

* P < .05

b_T1/2(h)= time taken for half the material in eachsample to be degraded in the rumen

The results from the in vitro and in sacco determination compare fairly well with the in vivo results. There was a tendency for underestimation of straw with low digestibility with the in vitro method whereas the in sacco method seemed to underestimate the digestibility of straw with a high in vivo digestibility. The reason for this might be that the rate of passage through the forestomachs is lower for untreated straw and higher for wet-treated straw relative to the 48 h incubation in vitro and in sacco. Solubilization of indigestible substances in vitro and in sacco would have the same effect.

In any case, the potential for improving the quality for various materials should be given some consideration before embarking on a comprehensive research programme. A screening by use of the in sacco or in vitro technique could be a useful tool here.

Availability and cost of chemicals and equipment

One of the most obvious prerequisites when planning chemical treatment of straw is that the chemical must be available at an acceptable price. If some special equipment like plastic tubes, plastic sheets, cans, pressure tanks etc. are needed this should also be available and not too expensive. As far as price of chemicals is concerned, it is difficult to generalize. Some countries produce their chemicals locally and can sell them at a moderate price whereas others have to import the chemicals and they make the price high to reduce currency outflow.

Prices are also changeable; high prices may be due to small sales volume. If a market is developed and a distribution network is built up the price may drop dramatically. Therefore there is no reason why these factors should be looked upon as constants.

Infrastructure

To be able to utilize the crop residues and the agro-industrial by-products as feed, a certain level of infrastructure is needed. It is needed for transport of materials, chemicals etc. It ought to be said, however, that a technology should be found that could be applied even with a minimum of infrastructure. In most situations this factor would not be considered a serious limitation.

Adverse effects of chemicals

One question that has to be asked when planning a research project on chemical treatment of fibrous by-products is whether or not the chemical in question has any adverse effect on the animals or the environment. Large quantities of alkali are thought to have undesirable effects upon the health of the animals consuming these feeds. Long term experiments in Denmark over at least 3 lactations with 40% dry (NaOH) treated straw in the diet have not revealed clinical sign of sickness among the animals (P E Andersen, personal communication 1983). In Norway, individual cows have consumed 700 – 800 g of NaOH in Dip treated straw for short periods (weeks) without showing any indications of health problems. One may conclude from the evidence available at present that the knowledge about alkali (NaOH) tolerance in farm animals is somewhat limited. Further studies at this point are therefore desirable.

Ammonia used for straw treatment is not considered to represent any health problems under normal circumstances whereas the risk of urea poisoning is well known and should be recognized.

In Norway, NaOH treatment of straw according to the Beckmann procedure has been practiced for more than 40 years. By this method the excess NaOH and some organic matter from the straw is washed into rivers and lakes. This has caused a pollution problem which is not accepted any longer from an environmental point of view. “Closed methods” have therefore been developed. By these methods all the chemical (NaOH) absorbed by the straw passes through the animals and is excreted through the urine and faeces. If the yearly precipitation is high, this is not considered to cause any soil pollution. In arid areas, this is a point that deserves special attention (salinity).

Governmental support

There is no doubt about the technical feasibility of many of the methods developed over the last decades. An economic assessment of the methods is therefore pertinent. To obtain a certain degree of precision, this assessment must be done locally because the conditions differ so widely.

One rule of thumb might be that the treatment is economical if the cost of treating 100 kg of straw is less than the value of the energy (metabolizable energy or feeding units) gained by the treatment. With the ammonia or urea treatment the “protein” value of the chemical should be added.

To encourage farmers to use fibrous by-products as a feed resource, and to save foreign currency, some countries offer financial support to those who treat straw chemically. In some countries such as Bangladesh the price of chemical (urea) is subsidized by the Government. In other countries the support may be given to the farmer based on the quantity of straw treated. If imported cereals for animal consumption is subsidized, there is no reason why support should not be given for upgrading of by-products for feeding.

Research programme

All the points above need not be equally stressed in the feasibility study. For some of them the answers are quite obvious whereas other questions need more investigations. If the conclusion from a feasibility study is positive and one or two treatment methods are selected for further studies under the prevailing conditions, planning of a research programme could start. Countries in which straw and other crop residues constitute the major part of the diet for the farm animals should give priority to research on utilization of these feed resources. A research programme in this area may be organized in different ways. One approach is the proposal put forward by Jackson (1978) in his excellent report. In spite of the new developments that have taken place since 1978 many elements of his proposal are still relevant. For the following, I have described an example of how such a research programme could be set up.

The research programme could be divided into three projects which should be closely linked to each other.

• Basic research
• Applied research
• Field research

One person could be in charge of each of these three projects and one could serve as a coordinator. The three or four persons should work as a group and they should meet frequently to discuss problems and administrative matters. The importance of getting hold of well-qualified persons for these jobs should be emphasized.

Instead of dividing the research programme into two or more phases, I would start the activity in all three projects at the same time. This is because I believe that practical problems in the field are even more important to solve than the technical and biological ones. Problems that one comes across in the field may need basic as well as applied research to be solved. Practical problems may also take longer to solve than problems of more basic and applied nature.

Basic research

Basic research may be needed to study a great number of factors that may influence the effect of a treatment: e.g. dosage of chemical, time of treatment, moisture content of the material etc. Laboratory research is also useful for screening purposes in which a number of materials may be tested as to their initial value and their response to chemical treatment. Fundamental studies on rumen fermentation, rate of passage and measurement of digestibility may be useful to enable the project personnel to draw general conclusions and to solve problems that cannot be studied in a field situation.

These type of studies may well be undertaken at universities and some experimental stations. Often such research is suitable for post-graduate students and visiting scientists. Findings from such experiments are important also for the teaching of other students. I believe that higher education should be strongly linked to the ongoing research in the field. This is particularly important in an applied science such as agriculture.

Applied research

Feeding trials at the production level are necessary to prove the value of a feedstuff in a real situation. Such experiments should be carried out at university farms or experimental stations with a sufficient number of animals to enable the researcher to show significant differences statistically. Young, growing animals may be used for this purpose and 10 to 15 animals per treatment would usually be required. The animals should preferably be fed individually and the feed should be weighed every day. The animals should be weighed regularly (every month). If the animals are slaughtered at the end of the experiment the carcass quality should be judged. If lactating animals are used the milk production should be recorded at least 4 to 5 days per week. The animals should normally be fed ad libitum (e.g. 10 – 15% left overs). If restricted feeding is practiced, periods of at least 2 – 3 weeks of appetite feeding should be included to allow estimations of feed intake. An economic appraisal of the results should also be carried out.

Efforts should be made to balance the diet with regard to protein, minerals and vitamins. Since concentrates are scarce in most developing countries, by-products from the milling industry, fishing industry and slaughter houses are often the most common feed supplements. Small amounts of fresh grass, weeds, water plants (e.g. Water hyacinths and Azolla), Leucaena and others have also proved to be valuable supplements.

The potential for NPN (urea) utilization should also be explored in such situations. Treatment of crop residues with urea/ammonia has the advantage over NaOH in that it increases the N-content of the material by 0.5–1.5%. This nitrogen is undoubtedly used to some extent by the rumen microbes for protein synthesis. On top of this, small supplements of undegradable protein may improve the performance of the animals considerably. The role of supplementation for an optimal utilization of diets based on fibrous residues and by-products is discussed in depth by Preston and Leng (1984).

There has been a tendency for university teachers to consider themselves very academic in that it is not their role to do a practical job in the field. In applied science it is absolutely necessary that the teacher throw off the white coat and work with his hands. Only when theoretical skill is combined with practical work can results of practical and economic value be obtained. In a starving world we cannot afford to play with research of pure academic interest. This is particularly true for agricultural scientists who have a greater responsibility here than most other scientists. This should be a challenge for the agricultural universities in developing countries. They should take the lead in the struggle for a real development of the country. Many scientists from developing countries go to Europe or USA for training in sophisticated laboratory techniques. When returning home they continue with their laboratory experiments instead of using their knowledge for the good of their countrymen. Why? The reason is that many universities in developing countries have inherited the evaluation system of many Western Universities which is based on number of publications rather than the applicability of the results. More credit should be given for work that contributes to the solution of the more serious problems of their farmers, particularly the poor ones.

There is also a risk that European and other visiting experts may run into the same pitfall. As mentioned before there is also a risk that the expert will compare the performance of the native animals (e.g. 2 – 3 litres milk/day) with that of exotic breeds fed high concentrate diets in Europe (20 – 25 litres milk/day) and hence try to transfer Western technology uncritically without appreciating the fact that in many countries the animals are of multipurpose types. Milk production may simply be given second or third priority after draught power, or production of faeces (fuel). This applies mainly to the conditions in South East Asia, Egypt and some other high potential areas. In regions with plenty of grazing areas the problems are different. Here the feed supply is abundant in the rainy seasons whereas treated by-products may serve as a valuable feed resource in the dry seasons. Such feeds are of particular importance in an emergency situation when the rains are late or fail to appear. In such areas the applied research should be conducted to give maximum information about how the problems in such situations should be tackled.

If drastic negative effects may be expected from a treatment, the experiment should be carried out in an experimental farm or at a university farm and not in the field.

Field research

Since much technical knowledge already exists, work should start at the field level as soon as possible. It is not so necessary to introduce a package of technology, but rather to become familiar with the local conditions and identify the problems that may arise when attempting to introduce a new technology. Under such a scheme three experimental diets could be tested.

• Traditional feeding.
• Diet based on untreated straw + urea and minerals.
• Diet based on treated straw + urea and minerals.

Other supplements may also be of interest depending upon the local conditions.

Experiments should be carried out at agricultural schools or at private farms with sufficient numbers of animals. The farmers chosen should be clever and motivated to cooperate. If possible the hosts for field experiments should be gathered at the beginning of the project to be introduced to the research plans and the actual methods for treatment. The possibility for cooperative treatment of crop residues, for instance on a village basis, should be explored.

Crucial for a successful project is that the person in charge of the field research has a solid theoretical background and practical experience. He/she should have practiced straw treatment elsewhere or worked for some time under a person well qualified in the field.

The project leader should have sufficient funds to buy the chemicals and small items needed for the research work. Funds will also be necessary for transport and technical assistance.

The field research will include treatment of the material under the control of the project leader, planning of the trials and the actual research work. Occasional weighing of the rations (one or twice a month) may provide some information about the intakes of straw. Weighing of animals is often a problem in the field, but chest measurements may give an indication of growth rates and body development. Milk production is, of course, easy to measure in lactating animals.

Samples from the feeding trials may be taken to the experimental station or the university for simple chemical analyses (e.g. degradability in sacco) to characterize the quality of the untreated and the treated material. An economic evaluation of the treatment is desirable as far as this is possible under primitive conditions.

If the wanted chemical is not available locally, the project leader should investigate how to get hold of it. If it is available, but at a very high price, the project leader should purchase a greater quantity which normally results in a price reduction.

A number of other problems may also arise, problems that may be difficult to foresee. However, frustration will not lead to any good. It is better to face the problems, and try to solve them trusting that a successful use of crop residues and agro-industrial by-products as feed sometime in the future will mean a better life for millions of people throughout the world.

Administrative matters, coordination

The leaders of the field, applied and basic research should form a group that meet frequently to discuss common problems, the progress made and the future of the research programme.

As part of the procedures for research into the topic training courses may be arranged for technical personnel at each centre. Some key persons may even go abroad for technical training: not to learn a technology which could be transferred directly, but rather to learn some basic concept with regard to treatment of fibrous by-products.

International seminars and workshops such as those organized recently in Bangladesh, Sri Lanka, Tanzania, Kenya, Egypt and elsewhere are stimulating for the participants who get an opportunity to discuss common problems and exchange information with colleagues with similar interest. It is also important that treatment of fibrous by-products is discussed in relation to various systems for animal production to place it in a broader context.

In spite of the many seminars organized, there seems to be a lack of information between the various groups working in this field. Therefore the proposal came up at the workshop in Alexandria last year that an information officer be employed for a period of 3 to 5 years who could disseminate information among the various groups. We hope that this idea will materialize before the end of this year and that the international development agencies in the Nordic countries jointly will sponsor this key person.

When starting from scratch, a minimum of 4 – 5 years of research should be allowed before the development of a practical system for by-product treatment can be expected. After that, an implementation phase would be logical, which might take 5 to 10 years, depending on the level of “development” of the country.

Conclusions

It is not possible to describe procedures for research into treatment of agro-industrial by-products and crop residues that will fit all types of circumstances. Some view-points of general character are outlined.

Before starting a research project on this topic, a feasibility study should be carried out to identify some of the relevant problems and to start with a right approach. Information that could be of interest in such a study might include:

• Amounts, quality and distribution of materials
• Alternative uses of the materials
• Alternative feeds and feed supplements
• Level of technology in the agricultural sector
• Potential benefit expected due to treatment
• Availability and cost of chemicals and equipment
• Adverse effects of chemicals
• Possibility of governmental support

A research programme on crop residues and agro-industrial by-products may be carried out at three levels: a) basic research; b) applied research; and c) field research. These are equally important and should run more or less parallel.

Basic research should be carried out on university or experimental farms where fundamental problems are studied. Field research should be carried out at well-run private farms, governmental farms and the like. Here, practical aspects of by-product utilization should be studied and the “bottlenecks” of the technology uncovered.

Solid training of the personnel employed is vital for a successful project and action should be taken to ensure a rapid flow of information between the various groups working in the field of by-product utilization.

It is difficult to recommend one particular method for treatment because this will depend on the conditions. In many tropical countries it might be logical to think of urea treatment as the first alternative.

REFERENCES

Jackson, M G 1978 Treating straw for animal feeding, FAO. Animal Production and Health Paper 10.

Jackson, M G 1981 Preface to Maximum Livestock Production from Minimum Land, Bangladesh Agricultural University, Mymensingh, Seminar 2–5, February 1981.

Kossila, V 1984 Location and potential feed use. In F. Sundstol and E Owen (eds): Straw and other fibrous by-products as feed. Elsevier, Amsterdam (in press)

Kristensen, V F 1984 Straw in practical diets for cattle, with special reference to developed countries. In F Sundstol and E Owen (eds); Straw and other fibrous by-products as feed. Elsevier, Amsterdam (in press).

Mwakatundu, A G K and Owen E 1974. In vitro digestibility of sodium hydroxide treated grass harvested at different stages of growth. East Afric. Agr. For. J. 40 1–10

NLVF (Norweigan Agric. Research Council) 1982. Energibrul ved ulike driftsformer i jordbruket, og muligheter for a redusere bruk av energy. Report

Sundstøl, F and Matre, T 1982 Bruk av ammoniakkbehandlad halm i kjøttproducsjonen Husdyrforsoksmøtet Agric Univ Norway

Sundstol, F and Owen, E 1984 Straw and other fibrous by-products as feed Elsevier, Amsterdam (in press)

Wanapat, M Sundstol, F and Garmo T H 1984a A comparison of alkali treatment methods to improve the nutritive value of straw. I. Digestibility and metabolizability (in manuscript).

Wanapat, M Sundstol, F and Hall J M R 1984b A comparison of alkali treatment methods to improve the nutritive value of straw. II. In sacco and in vitro degradation relative to in vivo digestibility (in manuscript).

VALIDITY OF FEEDING STANDARDS AND DEVELOPMENT OF FEEDING SYSTEMS BASED ON CROP RESIDUES AND AGRO-INDUSTRIAL BY- PRODUCTS

T R Preston
(FAO Consultant)

Graduate School of Tropical Veterinary Science
James Cook University
Townsville Q4811 Australia

SUMMARY

Feeding standards and computer formulated least cost rations have markedly improved the efficiency and profitability of pig and poultry production throughout the world. In ruminants, feeding standards are useful as a general guide for planning purposes. But for energy and protein, even with high quality feeds, differences between predicted and realised animal responses may reach as high as 30%. The discrepancies are even greater when sugar-containing by-products and fibrous crop residues form the basis of the diet.

The basis of the problem is in the dual mode of digestion in ruminants where gastric digestion is both preceded and followed by microbial fermentation. Sugar-containing by-products and fibrous crop residues contain no starch and insignificant amounts of protein, necessitating major dependence on fermentation as the digestion pathway.

It is hypothesised that the digestion end products resulting from microbial fermentation of sugar and fibre-rich feeds are deficient in glucogenic precursors as well as amino acids and that this is a major constraint to animal productivity.

To develop effective feeding systems with crop residues and by-products, the more appropriate method is by strategic supplementation (with or without chemical/physical treatment of the basic resource) in the following sequence:

• Fermentable nitrogen (urea, ammonia or poultry litter) to ensure levels of rumen ammonia do not fall much below 10mg/100 ml rumen fluid
• Small amounts (<25% of diet DM) of high quality green forage, preferably legume, to stimulate rumen function and fermentation
• Small amounts (<5% of diet DM) of good quality that will escape the rumen fermentation (by-pass protein)
• Improve the balance of the digestion end products by feeding “by-pass” starch or manipulate the rumen fermentation so as to increase the production of propionic acid and/or decrease the population of protozoa.
• Increase the degradability of the basal diet by alkali or acid treatment
• Repeat the supplementation sequence.

INTRODUCTION

To develop viable livestock feeding systems, it is necessary to relate information on the nutritional attributes of feeds with the needs of animals according to their purpose and productivity.

In countries with highly developed livestock industries, this information has been incorporated in “feeding standards” which interpret measures of chemical composition of feeds in terms of their likely capacity to supply energy and amino acids (and the micro-nutrients, minerals and vitamins) needed by the animal. These feeding standards have steadily become more sophisticated in an attempt to improve their predictive capability, and hence their usefulness for deriving least-cost formulations.

The issues to be debated in this paper are:

1. the validity of the feeding standard approach (presently used in the industrialized countries) as the basis on which to devise practical livestock production systems in developing countries where the feed resources are mostly crop residues and agro-industrial by-products;
2. how to characterize feed resources in a way that will facilitate their incorporation in feeding systems, bearing in mind the physical and financial constraints suffered by most analytical laboratories in agricultural institutions in developing countries, especially those situated in the tropics;
3. how to develop livestock production systems when the principal feed resources are crop residues and by-products.

The hypothesis that is put forward can be summarized in the words of Graham (1983). “Feeding standards are an outmoded concept in ruminant nutrition”.

A distinction is drawn between ruminants and monogastric animals because the use of feeding standards is only being questioned in the case of ruminants. Significantly, the basis of the problem is in the mode of digestion in this species, and specifically the role played by rumen microorganisms.

ANIMAL RESPONSE TO NON-CONVENTIONAL FEED RESOURCES

It is relevant to point out that doubts about the usefulness of feeding standards for ruminants in developing countries began to be manifested at the time that the first feeding systems were being established in Cuba using non-conventional feed resources such as molasses (Preston and Willis 1974). The issue was further emphasized as the results of experiences in Asia with alkali-treated straws (Jackson 1978).

The significant features of these developments were not the feeding of molasses or the alkali-treated straw, since both these feeds had been in use for decades in the industrialized countries, without giving cause for doubting the nutritive value of these ingredients, as assessed by conventional methods. The difference was in the magnitude of the contribution of the molasses and the straw to the animals' diet. This rarely exceeded 10–30 percent in the industrialized countries as there was ample availability of high quality feeds such as cereal grain and protein-rich meals to complete the diet. In contrast, the feeding regimes planned around molasses and straw in developing countries envisaged these ingredients supplying the major part of the ration, due to physical (availability), financial (high cost) and political (competition with human nutrition) constraints attached to the use of cereal grains and protein meals.

One characteristic common to both molasses and to alkali-treated straw is the magnitude of the response to small amounts of proteins of high biological value when this is in a form which can escape the rumen fermentation (e.g. fish meal) (Figures 1 and 2). These responses are much greater than is observed when comparable amounts of fish meal are added to a cereal grain-based diet (Orskov 1982).

The second common feature of molasses and alkali-treated straw is that even when supplemented with fish meal, the efficiency of utilization of the digested energy is considerably less than what is observed when the basal diet contains appreciable amounts of cereal grain (Redferne and Creek 1973). This “inefficiency” is particularly noteworthy when the host animal has a high glucose demand (e.g. for lactation) (Clark et al 1972; Perdok et al 1982; Chopping et al 1980, and personal communication).

What distinguishes molasses and alkali-treated straw from cereal grains is the complete absence of starch, the negligible content of protein, and relatively high concentrations of soluble sugar. In other words, the nutrients in molasses and in alkali-treated straw are only digested in the rumen; in contrast, the nutrients in cereal grains can be digested either in the rumen or in the intestine.

Figure 1:
Small amounts of fish meal improve the performance of steers fed a basal diet of molasses/urea (Preston and Willis 1974)

Figure 2:
Small amounts (50 g/d) of fish meal increase dramatically the performance of cattle fed ammonia (from urea)-treated rice straw in Bangladesh (Saadullah et al 1983)

Many of the reasons for the failure of feeding standards to predict attainable levels of performance on molasses and straw-based diets can be explained by interactions and associated effects among nutrients and between nutrients and their sites of digestion.

THE BASIS OF FEEDING STANDARDS

Before presenting some evidence which justifies the above statement, it is relevant to summarize the premises on which most ruminant feeding standards are based. These are:

• the protein supply to the animal is the sum of the microbial protein and the undegraded feed protein leaving the rumen plus a small endogenous fraction. The microbial protein is calculated from the organic matter consumed and the rumen degradable nitrogen, on the basis that 30 g of microbial N are produced for every 1 kg of OM fermented;
• the efficiency with which digested or metabolizable energy is used for productive purposes is a function of the concentration of digestible energy in the diet.

The premise underlying prediction of protein supply is biologically correct, but cannot allow for the dynamic effect of protein supply to the intestine being a direct determinant of organic matter intake. This is especially important when the basal diet is highly digestible but the protein supply is limiting.

DIGESTIBILITY, PRODUCTS OF DIGESTION AND PRODUCTIVITY

The use of the digestibility of the diet as the independent variable from which to predict net energy (ARC 1980) was challenged by Leng and Preston (1976). They hypothesized that poor ruminant productivity on highly digestible tropical feeds, rich in sugars and cell wall compounds but low in protein and starch, was due to an insufficiency of glucose and glucogenic precursors in the digestion end products. Since that date, results of other experiments have become available - mostly using “temperate” feeds - which strengthen considerably the original arguments.

Thompson (1978) reported that the efficiency of utilization of ME for tissue synthesis was higher for concentrate/forage combinations of maize and clover than for barley and rye grass even though the metabolizability of the dry matter DM (ME/DM) was the same on all diets (Table 1). One explanation is the proportionately greater post-ruminal digestion on maize/clover compared with barley/grass.

Work in Australia (Table 2) showed that pangola grass was used more efficiently (28 %) than setaria grass (17 %) for tissue synthesis in cattle although both had the same digestibility and were fed at the same rates (Tudor and Minson 1982); the authors mention the superior glucogenic potential of pangola as one possible explanation for the difference.

Rice polishings (with a large proportion of broken rice grains) were better than cassava root meal for supplementing sugar cane (Preston and Leng 1981). The starch in rice polishings escapes rumen fermentation almost quantitatively (Elliot et al 1978) whereas the starch of cassava root meal is fermented rapidly in the rumen (Santana and Hovell 1979). Glucose entry rates were higher when rice polishings rather than cassava root meal was the supplement in sugar cane diets (Ravelo et al 1978).

Supplementary energy as maize grain (with good rumen escape characteristics) improved feed conversion efficiency in cattle fed sugar cane whereas the same amount of molasses energy (completely fermented in the rumen) depressed feed efficiency (Donefer E, cited by Pigden 1972).

Cattle nourished by rumen infusion of VFA and abomasal infusion of casein increased their nitrogen retention as the proportion of propionic acid in the infused VFA was increased (Figure 3).

Convincing evidence concerning the need for glucogenic compounds in the end-products of digestion was provided by Tyrrell et al (1979) (Figure 4). Acetic acid infused into the rumen of animals receiving a basal diet of low glucogenic potential (alfalfa hay) was less efficiently utilized for tissue synthesis than when the infusion was given with a basal diet of high potential for providing glucose (60% maize grain and 40% hay).

The superiority of propionic acid for fat synthesis compared with acetic acid, observed in the original work of Armstrong and Blaxter (1957a, b) and Armstrong et al (1958) and the absence of differences between these two fatty acids in the experiments of Orskov and Allen (1962) can also be explained in terms of the glucogenic potential of the basic diet. The diet used by Armstrong et al (1958) was dried grass whereas Orskov and Allen (1962) gave the different VFA mixtures to animals fed mainly on barley grain.

The reason for the greater awareness in tropical countries of the role of glucogenic compounds in the end-products of digestion of ruminant diets is easily explained. In almost all temperate countries, the diets for high producing ruminant animals contain at least 50 % of cereal grains. Such rations give rise to relatively large quantities of propionic acid in the rumen fermentation and there can be considerable escape of the starch for post ruminal digestion to glucose. Furthermore, most of the dietary nitrogen is in the form of true protein, and absorbed amino-acids can spare glucose. There is thus rarely a deficiency of glucogenic compounds in the end-products of digestion. In contrast, tropical feed resources of high digestibility usually are of low glucogenic potential since they frequently contain carbohydrates (sugars) which are totally fermented, and give rise to VFA mixtures rich in butyric and acetic rather than propionic acid (Marty and Preston 1970).

Figure 3:
Relationship between molar proportion of propionic acid in the mixture of VFA infused into the rumen of sheep and the N retention (diet comprised only VFA infused into the rumen at maintenance level of feeding and casein infused into the abomasum) (Adapted from Orskov et al. 1979).

Figure 4: Acetic acid (infused into the rumen) is utilized more efficiently when the diet has a high content of con- centrates (from Tyrrell et al 1979)

Thus with feeds of temperate origin, increases in nutritive value are brought about by an increase in the proportion of cereal grain and oilseed meal in the diet and this gives rise to concommitant increases in the concentration of glucogenic compounds in the end-products of digestion. By contrast, in most tropical countries, cereal grains and protein-rich meals are in short supply and are competed for strongly for human and monogastric nutrition. They are available for ruminant feeding in only small amounts. Improvements in digestibility of feeds in such regions are brought about either by the inclusion of sugar-rich by-products (e.g. molasses) or by treatment with alkali/acid to hydrolyse resistant cell wall compounds. Raising the amount of sugar in the diet, or partially hydrolysing the cell walls in crop residues, does not lead to an increase in glucogenic compounds in the end-products of digestion, since neither of these strategies increases the liklihood of rumen escape of digestible carbohydrate. In addition, rumen fermentation of such modified feeds is characterized by relatively low proportions of propionate at the expense of butyrate (for sugar-containing feeds) or acetate (for alkali or acid-treated crop residues;) Table 3.

What is quite clear is that diets based on molasses or alkali-treated straw may be more digestible, but they support little or no improvement in animal productivity until they are supplemented with by-pass nutrients (Preston and Leng 1983); or the rumen fermentation is manipulated to raise propionate production (by feeding monensin) (H Ghulam and T R Preston, unpublished data), and/or protein supply to the intestine (by eliminating protozoa) (Bird and Leng 1978; Demeyer et al 1982).

The conclusion from the above discussion is that digestibility is a reasonable indicator of energetic efficiency for diets rich in starch and protein, but that it can be quite misleading applied to rations based on crop residues and agro-industrial by-products.

DEVELOPMENT OF FEEDING SYSTEMS

Nutrient requirement for production

The overall balance of nutrients: The principal functions of large ruminants, where low quality pasture and crop residues are the main energy resource, are workpower, growth, pregnancy and milk production. Beef is very much a by-product being the residual or salvage value of the unproductive animals. In order to derive feeding systems for these different productive functions it must be appreciated that the nutrient requirements cannot simply be satisfied by optimizing rumen microbial activity (i.e. total rumen digestion).

One of the most important objectives of ration formulation is to increase the voluntary intake of the basic resource, since this is frequently the first constraint. Secondly, as indicated earlier, it is the overall balance of nutrients available to the animal, not simply the products of rumen digestion, which determines productivity and feed utilization efficiency.

To understand this latter aspect, it is convenient to identify the specific nutrients that are needed for metabolism when the purposes of the feeding systems are to support such diverse functions as work, growth, pregnancy and milk production (Figure 5)

The greater part of the digested energy is undoubtedly needed for the animal to work both in the physical and metabolic sense. This can be defined as oxidation energy provided by nutrients which give rise to two-carbon fragments (C₂) catabolized in the Krebs or tricarboxylic acid (TCA) cycle. However, small amounts of energy in the form of glucose, or as compounds which can substitute for glucose and are glucogenic, are needed to catalyze the TCA cycle which is the mechanism by which oxidation energy is made available to the animal. There is an even larger requirement for these compounds to supply reduced cofactors (NADPH) needed for the elongation of the fatty acid chains in the synthesis of body fat and also milk fat. (MacRae and Lobley 1982)

Figure 5:
Ruminant reaquirements for major metabolites according to productive state

Glucose is the major energy nutrient for utilization in the brain and the central nervous system. It is also needed for macro-molecule synthesis in tissue growth and to form glycerol in fats and lactose in milk. Glucogenic compounds may also spare the catalolism of some of the essential amino acids. For simplicity, glucose and glucogenic compounds can be referred to collectively as energy for synthesis or C₃ - C₆ energy; the remaining major nutrients are the amino acids which are also needed for synthetic purposes, namely of body tissues and the proteins in milk.

All digested nutrients can give rise to oxidation energy but not all of them can supply glucogenic compounds and glucose or amino acids. The main glucogenic precursor in ruminants is propionic acid produced in rumen fermentation. Glucose can also arise from post-ruminal digestion of starch (by - pass or escape starch); certain amino acids are also glucogenic and can provide precursors for glucose synthesis following deamination. Amino acids are mainly derived from microbes grown in the rumen and the subsequent digestion of these organisms in the intestine; the second important source is from the post-ruminal digestion of dietary protein (by-pass or escape proteins).

These three groups of nutrients - oxidation energy, glucogenic compounds and essential amino acids - are required in different proportions according to the productive state of the animal. The total requirement for energy is perhaps known with most precision and, for the purposes of ration formulation, can be described in terms of metabolizable energy (ME), or simply digestible energy (DE) intake, since ME is usually calculated from DE. The capacity of feed ingredients to give rise to glucogenic compounds, glucose and to the amino acids will depend on a number of factors many of which interact with each other (Figure 6). This makes it difficult to establish a simple additive system for ration formulation.

Figure 6:
Origin of principal metabolites in ruminants

Amino acids: The supply of amino acids of microbial orgin to the animal will depend on the intake of fermentable feed and the efficiency of net microbial growth. The latter is controlled by a number of variables including rumen dilution rate, the presence of protozoa and the supply of precursors including fermentable N and minerals. For all practical purposes the amount of microbial protein derived from fermentable energy can be predicted on the basis of 3 g nitrogen per 100 g of digestible organic matter consumed. The other source of amino acids to the animal which becomes increasingly important as the productive rate increases (especially milk production) is the protein which escapes fermentation and contributes amino acids directly following digestion in the small intestine. The capacity of a protein meal to escape the fermentation is not only a function of the potential rate of breakdown of the protein by micro-organisms but it is also influenced by the dilution rate of rumen digestion as obviously the faster the flow of fluid and particles from the rumen, the greater the likelihood that they will escape rumen fermentation.

Figure 7:
Rate of glucose synthesis according to productive state in sheep (from Leng et al 1977)

Glucose and glucogenic compounds: The dietary nutrients which give rise to glucose and glucogenic compounds are those that lead to high rates of production of propionic acid in the rumen fermentation. In diets containing starch, glucose may become available directly if the starch can escape to the lower tract. The availability of glucogenic compounds is also enhanced by the amount of protein reaching the intestine as a number of amino acids provide three carbon units capable of being converted to glucose. Propionic acid production in rumen fermentation can be altered by chemical additives, such as monensin, which is widely used for this purpose in feedlot rations in Europe and North America.

When amino acid requirements are high, glucose synthesis rates (and therefore apparent requirements) are high (Figures 7 and 8). The pattern of apparent requirements for glucose follows closely that for amino acids suggesting that part of the requirement for amino acids may be a requirement for glucogenic compounds.

During growth and lactation, there may be competing needs for amino acids for glucose synthesis and for protein deposition. The important point here is that in growing, pregnant or lactating ruminants there is a high demand for amino acids for protein deposition, and for both amino acids and propionate for glucose synthesis.

Figure 8:
Requirement for amino acids in sheep according to productive state (from orskov 1970)

Figure 9:
Supplements of urea sweet potato forge and cottonseed meal increase the liveweight gain of cattle fed basal diet of derinded sugar cane stalk: open colwms refer to low urea and hatched columns to high urea. Lower part of columns for dry matter intake are the intake of the derinded cane stalk (from Meyreles et al 1979)

Requirements for amino acids and glucogenic compounds according to the productive state of the animal

As stated earlier, there is insufficient information available to permit the precise quantification of the proportions of the different nutrients required at the metabolic level for different productive states. Nevertheless, an approximation of the needs can be attempted, based on a scheme attaching relative priorities to the groups of nutrients together with knowledge of the physiological and biochemical processes underlying the expression of the particular productive state. Such an indicative scheme is set out in Table 4.

Work primarily involves a need for oxidation energy with minimum requirements for both glucogenic compounds (almost exclusively for the TCA cycle) and for amino acids (to repair the wear and tear of tissues and replace secretions). Maintenance alone obviously requires less energy expenditure. Late growth and gestation imply a relatively small increase in essential amino acid requirements. The requirements for growth in the young animal approaches that for high milk production, in terms of needs for amino acids and C₃ - C₆ relative to C₂ energy. Lower levels of milk production are obviously less demanding in terms of essential nutrients.

These priority ratings can be further simplified by assigning a ranking for each metabolite group according to the productive state being considered. Synthesis energy (C₃ - C₆) means the requirements for glucose and glucogenic compounds while the needs for amino acids are described in terms of supplementary by-pass protein (B-P) on the basis that the microbial protein supply will be determined by the energy status of the diet (Table 5)

NUTRITIVE VALUE OF FEEDS

The feed resources which concern us most in this Consultation are:

• Dry season pastures
• Crop residues
• Low value agro-industrial by-products

These feed resources will usually form the basis of the diet and generally will not be limited in quantity. The need is mainly to identify an appropriate supplement which should be tailored according to animal needs for the particular function under consideration. One role of the supplement will be to correct/complement the balance of the digestion end products in terms of the supply of amino acids and glucogenic precursors.

There is no adequate analytical means of assessing the potential value of feed ingredients as sources of amino acids, glucose and glucogenic precursors. The proportions of these nutrients in the digestion end products will be influenced by:

• the amounts of starch and protein in the feed
• the nature of the rumen microflora (ratio of bacteria to protozoa)
• the pattern of the fermentation (ratio of propionate to other VFA)
• the rate of fermentation of the feed
• the rate of passage of liquids and particles out of the rumen
• escape of starch and protein from the rumen (determined by the previous two factors).

The cheapest feed ingredients are the natural grazing and/or crop residues and, to a lesser extent, agro-industrial by-products which will constitute the energy sources; and non-protein nitrogen, in the form of urea and ammonia. The expensive feeds are the protein meals, derived from oilseed residues and the by-products from processing of animals, fish, and starch-containing cereal grains, which are also the staples of human and monogastric animal nutrition. In general terms, therefore, sources of oxidative energy and fermentable nitrogen are relatively inexpensive, while the sources of amino acids and glucogenic compounds (the protein meals, cereal grains and cereal by-products) are very expensive.

Since it is the combination of fermentable energy and fermentable nitrogen which gives rises to amino acids in the form of microbial protein, and as feeding level is associated positively with protein supply to the duodenum, it is generally desirable to supply the basal feed resource on an ad libitum basis. The fermentable nitrogen requirement can be predicted on the basis that 100 g of fermentable carbohydrate in the feed will give rise to microbial protein containing 3 g of nitrogen. Of course, it is not always necessary to provide the total amount NPN, since a proportion of the feed protein will always be fermented to ammonia and in addition considerable blood urea-N may be secreted into the rumen. These processes reduce the amount of non-protein, fermentable nitrogen needed.

The potential of the final mixed diet to satisfy the requirements of the animal for amino acids and glucogenic precursors depends principally on its content of protein-and starch-containing ingredients capable of escaping rumen fermentation and which are able to be digested in, and the products absorbed from, the intestine.

FORMULATIONS OF FEEDING SYSTEMS

The capacity of feeds to provide oxidative energy can be estimated relatively precisely from the digestion coefficients. These can be determined by a number of means; by total collection of faeces from animals fed ad libitum; from the 24-hours DM loss from nylon bags in the rumen; or from some appropriate in vitro fermentation test. By contrast, it is almost impossible to predict accurately, from analysis of individual feeds, the effect that combinations of these feeds will have on the final supply of amino acids and/or glucogenic compounds, at the levels required for efficient metabolism in the animal.

Two schemes are proposed in order to devise suitable supplementation programmes for achieving particular rates of productivity.

Least-cost complete rations:

The first scheme is for the computerized formulation of least-cost complete rations. The available basic feed resources and supplements are rated according to their potential to give rise to amino acids and glucogenic compounds in the end-products of digestion (Table 6). This information is then combined with the nutrient requirements according to the productive state expected of the animal (Table 5). These two sets of data are then incorporated in a computer model for least-cost ration formulation together with the traditional standards for the anticipated level of production for digestible energy, calcium and phosphorus etc.

* Contains no by-pass protein but it appears to support highly efficient rumenmicrobial protein production.

The limitations of this of this scheme are in the arbitrary assignments of the constraints for 3-C₆ energy and by-pass protein (B-P). The scoring is based on wide experience of, plus information from the literature on, the feeds in question. As such, the information is a form of substitute for “farming wisdom”, which is probably the most important input in ruminant production systems in the industrialized countries. This experience is usually lacking in most of the situations to which this Consultation relates:

Supplementation:

A more empirical scheme, which is more appropriate for the conditions of most developing countries, is to select the basal energy resource according to physical availablility and price and then to provide supplementary nutrients in accordance with their relative priorities (Table 7) and costs.

In this system, the first step is to provide a source of non-protein nitrogen (usually urea or ammonia) to raise the level of fermentable nitrogen to a minimum of 3 % of the digestible organic matter. It is desirable that this is done in a way which will ensure an almost continuous supply of ammonia-nitrogen to the rumen micro-organisms.

The second priority is to give good quality green forage, preferably legume, up to a maximum of about 0.7 % (DM basis) of liveweight (about 25 % of the diet) daily.

Finally, a protein-rich by-product of oilseed crushing or cereal processing, or an animal by-product meal, should be given in amounts not to exceed 20 % of the total diet DM. The 20% limit is to prevent depression/substitution of the digestible energy of the basal diet. Lesser amounts may be more economical, and it is imperative that response trials be carried out so that the amount of supplement can be related to the rate of animal productivity.

Two experiments carried out with agro-industrial residues composed almost entirely of soluble sugars and cell wall compounds and with extremely low contents of nitrogen and protein, corroborate the relevance of the above principle (Figures 9 and 10), and indicate that the best results from these feeds are achieved when all the supplements are combined into one feeding system.

In the case of the derined sugarcane (Figure 9), animal response was increased from 0 to 500 g/day live weight gain by either high quality for age or cottonseed meal. Nevertheless, performance was further increased by 100% to reach 1 kg/day when all the supplements were combined in the same ration. It is appropriate to note that high levels of urea only gave a response when both the good quality forage and/or by-pass nutrients were also provided.

The second trial (Figure 10) was with ensiled henequen (sisal) pulp. This feed resource is deficient in phosphorus and trace elements, highly imbalanced with respect to calcium and provokes a metabolic acidosis. There was no response in animal performance to supplements which neutralized the acidosis (Harrison D.G., personal communication) or which provided an appropriate balance of minerals (Figure 8). However, limited amounts of either a good quality green forage (Brosimum alicastrum) or a by-pass supplement (soybean meal) changed the liveweight loss in lambs of -40 g/d to a gain of 55 g/d. When all supplements were combined, the growth rate was increased to 125 g/d.

As in the case of the urea in the previous trial, there was no response to minerals (known to be deficient in the basal diet) until both rumen function and by-pass nutrient status were provided for by the combination of green forage and soybean meal.

Figure 10:
Liveweight gain of lambs feed a basal diet of sisal (henequen) pulp/urea, with and without a complete mineral mixture, and supplementes of good quality for age (Brosimum alicastmum) and/ or soybean meal (SBM) (from Rodriquez 1982)

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