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Chapter 8




8.1.1 Factors influencing nutritive value

In many developing countries, and in Asia in partic­ular, ruminants are fed on straw from cereal crops (mainly rice and wheat). As population pressure in­creases and the area devoted to food-crop produc­tion is extended the use of crop residues and byprod­ucts for animal feeding will increase. In countries with specialised livestock production systems, straw is considered of such low feed value that it is often burned, but in developing countries where livestock are integrated with cropping it is a valuable resource.

Draught animals appear to be able to work and to maintain body condition on a diet of mainly straw. Research on the utilisation of straw by ruminants in developed countries has focused on the role of straw as a roughage supplement in a concentrate diet. This aspect of the use of straw is not important in the context of "matching livestock systems to available resources". The following discussion emphasises the use of straw as a basal diet and the use of supplements to increase productivity.

The nutritional value of straw (see Sundstol and Owen 1984) varies according to a number of factors, including:

Table 8.1: Straws from various cereal crops appear to be highly variable in organic matter digestibility (in vitro) (OMD). The N content is always low
















Sorghum leaves



Source: Nicholson 1984


Table 8.2: In vitro true organic matter digestibility (True-OMD) and lignin content of sorghum leaf and stem from 24 varieties grown under the same con­ditions. Among leaves, 80% of the variation in di­gestibility could be accounted for by the range in lignin content. Higher lignin content was associated with the presence of insoluble condensed tannins in the fi­bre fraction. Variation in digestibility of both leaf and stem fractions of sorghum straw is likely to influence productivity of livestock consuming it and should be taken into account by plant breeders.


True OMD

(in vitro) (%)  


Lignin (% DM)


Mean (range)

Mean (range)


70 (62-79)

6.0 (4.7-7.1)


65 (53-74)

6.6 (5.1-9.1)

Source: J D Reed, unpublished data.

All cereal straws have two characteristics in common:

There appear to be no toxic substances in straws, except when they are mouldy. Rice straw, which forms a large proportion of the available forage in developing countries, contains high levels of oxalate and silica which are reported to be concentrated in the leaf rather than the stem. The lignin content of rice straw appears to be less than in other straws.

When straws are fed to ruminants the primary lim­itations to production are:

Treatment of straws to increase digestibility

The productivity of animals fed straw can be in­creased by treatment of the straw to increase di­gestibility and feed intake, especially when combined with correct supplementation. The use of treated straw with supplements also allows the use of ani­mals with higher genetic merit (Table 8.3). Methods for industrial-scale treatment of straw with alkalis (eg. ammonia and caustic soda) have been available for some time. In the developing countries the major problem with this approach is to find methods that are both acceptable and effective at the village level.

Table 8.3: Milk production and change in liveweight (L Wt) in Zebu and Holstein/Zebu cows in Bangladesh on basal diets of untreated or ammoniated rice straw (NH3-straw) (urea ensiled). The native animals per­formed best on the untreated straw, but the crossbreeds were superior when the degradability of the straw was increased by ammoniation.




Straw intake (g/d)









LWt change (g/d)









Milk yield (kg/98 days)









Khan and Davis 1981

In some European countries, caustic soda has been used to increase the digestibility of straw for more than 40 years. A number of other techniques are be­ing applied in large enterprises (eg. ammoniation) but these methods have not been generally accepted by small farmers. Methods for treating straw with caustic soda are rarely economic, are difficult to ap­ply and are hazardous to people and animals. Thus, treating straw with caustic soda is impracticable in most developing countries.

There are a number of ways in which ammonia can be used to increase the digestibility of fibrous feeds, including methods that use ammonia gas, am­monia in solution or ammonia generated from urea (see Chapters 5 and 12). Ammoniation of straw ap­pears to be potentially applicable to a wide range of situations. The choice of the method of ammoniation will depend on the cost and availability of ammo­nia gas relative to urea. Ammonia gas lends itself to large operations where there is the necessary infras­tructure for distribution of ammonia in cylinders or tanks. This may be readily done in oil-rich countries where ammonia gas is manufactured for agricultural purposes.

For small-scale farmers it is more convenient to gener­ate ammonia from urea by the "wet-ensiling process" . Urea is a common fertiliser which is often subsidised and which farmers have become accustomed to han­dling. It poses no hazard to human health but farm­ers are generally concerned about its possible toxicity to livestock. Ammonia is generated rapidly from urea at high temperatures when it is mixed with moist stra w, which makes the system appropriate for trop­ical but not temperate countries. A source of ure­ase may also need to be added for the more inert crop residues or fibrous byproducts (eg. bagasse; see Torres et ai. 1982). The ground seed from Jack­bean (Canavalia ensiformis) is being used commer­cially for this purpose in Colombia (Preston 1987). Urea-ensiling appears to be less effective than using ammonia gas because of the formation of ammonium carbonate, which decreases the pH of the straw (Mason et al. 1985).

Ammonia can be generated from other nitrogenous materials such as chicken manure but these tech­niques are only now being developed. The use of animal or human urine to ensile straw has been re­searched in Bangladesh (see Davis et al. 1983) and has shown promise for application on small farms. It is, however, essential to ensure an adequate level of urea in the urine.

Several other chemicals can be used to increase straw digestibility including calcium oxide, acids and acid gases (sulphur dioxide) or combinations of these. All these techniques are experimental and have not yet been proved to be applicable.

One method of treatment to increase the digestibil­ity of fibrous feeds which appears to have some ap­plications on an industrial scale is the use of steam at high pressures. This may be feasible where this energy source is available and inexpensive (ie. in sugar mills where there is usually surplus steam). The technique appears to be particularly appropri­ate for treatment of bagasse which is available on site at the sugar mill and where the necessary technical knowledge and equipment are also available.

Mineral content of straw
The mineral content of straws is generally low and imbalanced but deficiencies are unlikely to be mani­fested in animals at maintenance or working. For pro­duction of meat and milk, requirements for minerals are increased many-fold and supplements should be supplied. However, responses to mineral supplements will only occur after the major nutrient imbalances (protein and glucogenic energy) have been corrected. The mineral composition of plants depends largely on the availability of minerals in the soil and closeness to the oceans (for N a). Calcium and phosphorus con­tents of straw are usually below recommended levels and cobalt, copper, sulphur and sodium may also be deficient. The high concentrations of oxalates and silicates in rice straw also suggest that considerable amounts of calcium and magnesium salts can be lost as silicates and oxalates in urine and faeces.
8.1.2 Draught animals

Draught animals appear to work and survive on a wide range of fibrous diets and are able to tolerate the low digestibility of the diet and its low nitro­gen content. Working bullocks in Bangladesh con­sumed greater quantities of ammoniated rice straw (ensiled with urea) than their pair mates given un­treated straw but there were no apparent differences in work output or bodyweight change (Dolberg et ai. 1981). Further evidence that working animals require little protein supplementation is the finding that young horses that were exercised grew at the same rate on a low-protein diet as those on a high­protein diet that were not exercised (Orton et ai. 1985a). Recent work suggests that excessive protein in a diet can slow the race horse (Glade 1983).

In Pakistan, Preston (personal observation) ob­served bullocks driving a press, crushing 400kg of sugar cane per hour, working alternate shifts of 3 hours work followed by 3 hours for feeding and rest, and found that they were apparently able to work on this basis for 24 hours a day almost continuously for 6 months on a diet of only sugarcane tops. In con­trast, a diet of sugarcane pith of higher digestibility (70%), supplemented with urea and minerals barely supported maintenance in 'growing' steers (Preston et al. 1976). The exclusive use of sugarcane tops as feed for working oxen is common practice on sugar es­tates with a priority for employing people. Obviously the influence of exercise on nutrient requirements is a subject requiring a great deal of research (see Chap­ter 2).

8.1.3 Growing animals

Moderate rates of liveweight gain can be obtained with young ruminants on diets based on crop residues provided that a number of principles are applied. These are discussed below.

Green forage

A small quantity of highly digestible green forage apears to have beneficial effects on rumen function on diets based on crop residues. The results in Table 8.4 indicate that such improvements in the rumen ecosystem carry through to improved animal perfor­mance. Azolla pinnata, a water plant which grows symbiotically with the N-fixing alga Anabaena azolla, appeared to be even more effective than a mixed con­centrate meal in promoting liveweight gain in cattle fed a diet of wheat straw and sugarcane tops.


Table 8.4: Small amounts of the water plant Azolla pinnata appear to be as effective as a balanced concen­trate in improving the utilisation of a diet for cattle based on crop residues.




LWt gain (g/d)



Feed intake (kg DM/d)



Wheat straw+sugarcane tops









Feed conversion

(kg DM/kg gain)



OMD (%)



Source: Singh (1980).

1.*Contained: 65% maize meal, 15% rice bran, 16% groundnut cake, 4 % minerals.
**2.8% N in DM; 81 % digestibility of DM.


The advantage of using the foliages oflegume trees as "green" supplements is that these are rich in pro­tein (25 to 30% in dry matter), at least part of which appears to escape rumen fermentation. According to Bamualim et al. (1984)' leucaena leaf meal was as effective in stimulating voluntary intake of a low-N hay as was casein infused into the abomasum.


The data in Table 8.5 and Figure 8.1 confirm the effectiveness of leucaena foliage as a supplement for cattle fed basal diets of rice straw. In the feeding trial in Colombia, which involved 36 weaner steers fed ad libitum ammoniated rice straw for 90 days, fresh leucaena leaves (2kg/d) were as effective as 500g/d ohice polishings in stimulating liveweight gain (from 200g/d in unsupplemented animals to 550g/d with the supplements) (Figure 8.1).


Table 8.5: Leucaena foliage (+LF) increased dry matter intake and nitrogen retention in cattle given diets based on untreated or treated (sodium hydroide) rice straw (NaOH-straw).


Untreated straw

NaOH straw






DM intake, kg/d





DM digestion,





N retention, /d





Moran et al. (1983).
24 hours with 4 % $olution in 1:1 proportion.


Figure 8.1: Development of a cattle feeding system based on ammoniated rice straw. In phase 1, the basal diet of 6 groups of weaner bulls was ammo­niated straw (ammonia gas); the supplements were rice polishings at 0, 250 and 500g/d in the pres­ence or absence of fresh leucaena folzage (2kg/d). In phase 2, the treatments were ammoniated and un­treated rice straw with different levels of rice polishings. In phase 3, the treatments were ammoniated and untreated straw, the latter was supplemented with urea/S (Source: Preston 1987)


Lucerne hay comprising 13% of a diet based on maize cobs increased liveweight gain of cattle by 100% when the basal diet was untreated and by 50% when the maize cobs were treated with ammonia (Cook et al. 1982).

Bypass nutrients and glucogenic compounds

The role of these nutrients in growing animals is dis­cussed in Chapter 4. The data in Table 8.6 are from experiments in Australia with sheep fed oat straw.

Table 8.6: Formaldehyde-casein (Formal-C), rapeseed meal (RSM) and sunflower seed meal (SFM) (both meals with and without formaldehyde treatment) increased fibre digestibility, dry matter intake, liveweight gain and wool growth in sheep fed a basal diet of oat straw.









DM intake (g/d)







Digestibility (%)





















LWt change (g/d)







Wool growth (g/d)








Coombe (1985).







Figure 8.2 and Figure 8.3 relate to two feeding trials where the pattern of response to the supplement was measured. The results from the trial in Bangladesh are particularly interesting as they show that a daily supplement of only 50g of fish meal to cattle tripled productivity on a diet of ammoniated rice straw (Figure 8.3).


Figure 8.2: Feed intake, wool growth and liveweight gain of lambs given barley straw/urea and a bypass protein pellet (cottonseed meal 80%, meat meal 8%, soya bean meal 10%, minerals 2%) (Source: Abidin and Kempton 1981)




Figure 8.3: A small supplement of fish meal dra­matically Increased g1'Owth in live and carcass weight in young cattle fed a basal diet of ammoniated (urea-ensiled) rice straw in Bangladesh (Source: saadullah 1984)



Recent research in Thailand and Australia (Table 8.7 and Table 8.8) provides strong support for the concept that the critical supplementary nutrients on a straw-based diet are bypass protein, starch and long-chain fatty acids (see Table 8.8). High rates of growth were obtained when the ammoniated straw (urea ensiling in Thailand and ammonia gas in Aus­tralia) was supplemented with starch, protein and oil in byproduct meals that are known to escape rumen fermentation (Elliott et al. 1978a; 1978b).


Table 8.7: Effects of supplementation of ammoniated rice straw with a mixture of fat, protein and rice starch. Young Brahman bulls (36) weighing 150kg liveweight were used in an experiment lasting 153 days.


Supplement*, kg/d





Feed intake (kg/d)




Rice straw












LWt gain (kg/d)




Feed conversion




(kg DM/kg gain)




Source: Wanapat et al. (1986).
*The supplement contained rice bran 65.6%, broken rice 22.0%, soya bean meal 10.9%, bone meal 0.5%, $alt 1.0%


Table 8.8: The effects of various levels of by­pass-protein (largely cottonseed meal) supplement on the live weight change of cattle (320kg liveweight) given a diet of ammonia-treated or untreated rice straw, O.5kg molasses/block (15% urea) to provide fermentable N, and O.6kg rice polishmgs to supply small amounts of starch and lipid

Straw preparation


Protein meal) (kg/d)

LWt gain













Treated with 3% NH3 gas












Perdok and Leng 1987


The interaction between ammonia treatment of straw and response to bypass nutrients is illutrated in Figure 8.1 which summarises the perfor­mance of steers fed on ammoniated or untreated rice straw. During phase 2 (approximately 260-350kg liveweight), there were linear responses in growth rate to a supplement of rice polishings on both ammoni­ated and untreated straw. However, 2kg/d of the sup­plement was needed when untreated straw was given compared with only 500g/d to support the same rate of liveweight gain on ammoniated straw. The inter­action continued to be manifested during the final finishing phase of the cattle (350-450kg liveweight), when urea and sulphur were sprinkled on the untreated straw.1t can be concluded that ammoniation raised the availability of nutrients from straw and also led to a more balanced array of nutrients to the cat­tle since lower levels of dietary bypass nutrients were needed to optimise performance.

8.1.4 Long-chain fatty acids

Evidence which demonstrates the benefits of having a dietary source oflong chain fatty acids in straw-based diets is summarised in Figure 8.4. Lambs fed am­moniated wheat straw and minerals increased their growth rate and feed conversion in response to di­etary long chain fatty acids given in the form of in­soluble calcium soaps (Ca-LCFA). The response was only apparent when bypass protein was also given. Subsequent work confirmed the interaction between LCFA and bypass protein, and showed significant increases in carcass fatness in response to the LCFA supplement (given as long-chain fatty acid prills) (van Houtert and Leng 1987).


Figure 8.4: A supplement of long-chainfatiy acids (as insoluble calcium soaps) increased the growth rate of lambs fed ammoniated wheat straw and bypass protein (Source: van Houtert and Leng 1986).

From the discussion in earlier chapters it is obvious that fibrous crop residues can only support low milk yields in ruminants because of their inability to sup­ply enough protein and glucogenic energy to balance the VFA energy. These feeds are the most, and often the only, available resource on many small farms ill developing countries. Therefore every attempt should be made to use them as efficiently as possible. Milk synthesis represents a greater drain on critical nutri­ents than any other physiological state (Chapter 4).


In view of the nutritional limitations of most crop residues, set by low digestibility and low N content, and the high demand for amino acids, long-chain fatty acids and glucogenic compounds, milking an­imals must be given high priority for (i) the available supplements and (ii) the residues that have higher potential digestibility or that have been treated to improve digestibility. The scientific basis for feeding milking animals on crop residues is discussed in the following section.

Effect of ammoniation

Upgrading the nutritional value of straws by ammoniation (urea ensiling) is more likely to be economi­cally justifiable for lactating animals than for animals in other physiological states. In most circumstances the sale value of the extra milk produced should more than cover the cost of processing the straw.

Table 8.9: Milk yields and changes in live weight (L Wt) in cattle and buffaloes fed basal diets of un­treated and ammoniated (urea-ensiled) rice straw (NH3-straw)


Milk yield (kg/d)

LWt change (g/d)












2.4 (4.6)

3.4 (4.9)




2.4 (6.8)




Sources: Khan and Davis (1981)
1. All cows received 500g of rice bran/day and 200g of oiL~eed cake/kg of milk.
2. All cows r
eceived 1.5kg of concentrates/day.
3. A
ll buffaloes received 1.0 kg of con­centrates/ day.
igures in brackets are milk fat percentages.


The data in Table 8.9 summarise research from Bangladesh and Sri Lanka where ammoniated or un­treated rice straw was the basis of the diet for Zebu and buffalo cows. The cattle responded significantly to ammoniation of the straw, both in milk yield and in liveweight change. Ammoniation of the straw in­creased feed intake, and obviously reduced the need for bypass nutrients since the amount of milk produced per unit of concentrate fed was increased by an average of 53%. The proportion of the total diet represented by concentrates was reduced from an aerage of 14% to 9% due to increased intake of the treated straw (Table 8.10).


Table 8.10: Ammoniation of rice straw (NH3-straw) permits reduction in amount of concentrate required for milk production



NH3 straw

Concentrate (% diet DM)

Zebu x Friesian









Milk produced (kg/kg concentrate)

Zebu x Friesian

1. 7








Source: Preston and Leng 1984


Effect of green forage

The effect of green forage, in the form of gliricidia leaves ( Gliricidia sepium), is illustrated in Figure 8.5. On a diet of untreated straw, feeding gliricidia foliage at approximately 15% of the dietary dry matter in­creased milk yield by 22%. With ammoniated straw as the basal diet gliricidia comprised 10% of the diet and milk yield was increased by 14%.

Figure 8.5: Supplementation with fresh gliricidia fohage ( G) or ammoniation of straw (urea ensiling) (TRS) increased milk yield and body weight gain of buffalo cows and calves fed a basal diet of rice straw and 1 kg/day of concentrate (RS). Best results were obtained when straw was treated with ammonia and supplemented with gliricidia foliage (TRS/G) (Source: Perdok et al. 1982).
Bypass nutrients

The data in Figure 8.6 and Table 8.11 illustrate the results of trials in which responses to different amounts of protein supplements were measured. In Bangladesh there was a linear increase in milk yield in Zebu cows when fish meal was given as a supple­ment to a basal diet of ammoniated rice straw. Milk yield was increased by 23%, fat percentage by 8% and liveweight gain by 110% when 1000g of coconut cake were fed daily to lactating buffaloes in Sri Lanka on a basal diet of ammoniated rice straw and minerals.


Figure 8.6: Milk yield of native and crossbred cattle fed ammoniated (urea-ensiled) rice straw in Bangladesh was increased linearly with. small amounts of fish. meal (0 to 400g/d) (Saadullah 1984).


Table 8.11: Supplementing ammoniated (urea en­siled) rice straw with. coconut cake increased the milk yield and liveweight gain of buffaloes in S7'i Lanka.


Coconut cake, kg/d




Milk yield (kg/d)



Fat (%)



LW gain (kg/d)



Source: H Perdok, Unpublished data


8.1.6 Wool growth

The effects of strategic supplementation on wool growth in sheep are illustrated in Figure 8.7. Wool growth was increased when either a protein meal (cot­tonseed cake) or a readily-digestible forage (lucerne hay) was the supplement in a wheat-straw diet prvided with fermentable N by adding urea or by ammoniation of the straw.

Figure 8.7: Supplements that provided rumen "acti­vators" (lucerne hay) and/or bypass protein (cotton­seed meal) increased the wool g1'Owth of sheep fed a basal diet of wheat straw that had been sprayed with urea or ammoniated. There were additional benefits when the sheep were defaunated (Source: S H Bird, B Romulo and R A Leng, unpublished data.)


The combination of the two supplements gave the best results. Responses were more marked when the straw digestibility was increased by ammoniation and when the sheep were defaunated.


The data presented previously (Figure 8.2) suggest that the optimal wool growth response in growing lambs fed a barley straw/urea basal diet occurred when the protein meal (80% cottonseed meal, 10% soya bean meal, 8% meat meal and 2% minerals) comprised about 30% of the diet dry matter.

8.1. 7 Metabolic disorders associated with ammoniation of feeds

Adding ammonia to ruminant feeds to provide fermentable N has been researched for a number of years. In early trials, ammoniation of molasses was highly detrimental because the ammonia gas reacted with the sugars, increasing the temperature and ap­parently resulting in formation of toxic methyl im­idazole compounds which induced a severe nervous disorder (Tillman et al. 1957, Bartlett and Broster 1958) .


In countries with a temperate climate, ammonia­tion of straw (to increase digestibility) requires 3-6 weeks (versus 10 days or less in the tropics) because of low ambient temperatures. In order to reduce the treatment time, methods have been developed in which the straw is heated. Large ovens are manufac­tured in Europe to treat several tonnes of straw at 90°C, allowing the treatment time to be reduced to one day.


This practice has been commercialised in Europe and ammoniated straws have been fed to livestock with no reported ill-effects (H Sundstol, personal communication). However, ammoniated hays caused bovine hysteria when fed to cattle (for review see LaBore et al. 1984). The problem also occurs occasionally with ammoniated straw. This effect may be related to the proportion of the treated forage or straw in the animal's diet, since recent research in Australia (with one batch of rice straw and one of w heat straw) indicated that bovine hysteria devel­oped whenever the treated straw comprised a large proportion (70-80%) of the diet (Perdok and Leng 1985, 1987).


In studies by Perdok and Leng (1985, 1987), in which 64 yearling cattle were given thermammoniated rice straw from a failed crop, almost all the animals developed hyperexcitability, with the fol­lowing symptoms: animals were restless and blinked rapidly, their pupils dilated and their vision was ap­parently impaired; involuntary twitching, trembling, loss of balance and frequent urination and defeca­tion were observed. In addition, respiration rate was high, heart rate was low and the animals salivated copiously; they bellowed and perspired. The most obvious and most dangerous symptom was sudden stampeding: the cattle galloped in circles, were in­clined to collide with each other and also to run into fences. Often the animals galloped at such speed that they broke limbs, and in one instance an animal died. The symptoms usually lasted for 5 minutes and were repeated at 20- to 30-minute intervals. The affected animals appeared normal between these attacks and tended to return to feed on the treated straw. The condition was also induced in animals fed the same rice straw after it had been treated with ammonia under plastic sheets for 4 weeks (Perdok and Leng 1987).


The syndrome has occurred also in young calves suckled by cows consuming a diet containing a ma­jor proportion of ammoniated rice straw: both cows and calves showed symptoms. Pasteurised milk from these cows also caused the hysteria when fed to calves. Under some circumstances calves suckled by cows fed ammoniated hays have died. These obser­vations indicate that the toxic compound(s) is trans­mitted in milk and is unaffected by pasteurisation (Perdok and Leng 1987).


Bovine hysteria in cattle fed straw has not so far been reported from Northern Europe, possibly bcause the proportion of ammoniated straw fed rarely exceeds 30% of the total diet in intensive livestock feeding systems. A recent report from Southern Spain (Cabrera et al. (1987) has, however, shown that in warm climates feeding ammoniated straw to cattle and sheep can be extremely dangerous. Cabera et al. (1987) reported numerous cases of hypeexcitability and death in sheep and cattle fed straw when this was initially treated with ammonia gas af­ter 1100 hours and on a warm day in summer.


Ammoniation through urea ensiling is highly un­likely to result in toxic compounds being produced, particularly if the moisture content of the straw is kept high. It is advisable, however, always to pre­pare straw when the temperature is low.


The transmission of toxic compounds in milk from cows fed ammoniated forages suggests that care should be taken in feeding ammoniated forages to milking animals.



There are a number of fibrous residues that, un­treated, have only limited application as the basal component in livestock feeds (eg. bagasse, palm­pressed fibre, cocoa pods and rice hulls). The lim­itation to all these feed resources is their extremely low digestibility and, even when supplemented with essential nutrients, intake is too low to support main­tenance. They are, however, often used as fillers and sources of roughage in high-concentrate diets.

Most of these residues arise from industrial process­ing and are therefore available in large quantities at the factory site. The concentration of these byprod­ucts at the factories is an incentive to finding ways to use them as ruminant feeds by using 'relatively so­phisticated' technology to increase their digestibility. Techniques such as briquetting, steam treatment and ammoniation can be considered under these circum­stances.


The factories where these residues are produced usually have the infrastructure necessary to enable adequate servicing of the machinery that is normally required for any large-scale industrial treatment of a fibrous residue. Often the residue is used as fuel in the factory (eg. bagasse, palm-pressed fibre and peanut hulls), but frequently there are surpluses. Little re­search has been done on these residues, with the ex­ception of steam-treated bagasse which is now being used commercially in diets for cattle in both Brazil (E L Caielli, personal communication) and Colombia (Preston 1987).

Some of the original research on steam treatment of sugarcane bagasse was done in Mauritius (Wong et al. 1974). Treating the bagasse with high pressure (14kg/cm2) steam for 5 minutes raised dry matter di­gestibility from 28 to 60% (rumen nylon bag method; 48 hr incubation). Early attempts to use the treated bagasse as the basis of the diet for growing cattle focussed attention on the need to supplement with bypass protein (fish meal), LCFA and glucogenic pre­cursors (maize grain) (Table 8.12).


Table 8.12: Calves lose weight on a diet of steam-hydrolysed bagasse (200°C for 10 minutes) supplemented with only urea and minerals. Significant improvements in growth and feed conversion wr'e brought about when fish meal (bypass protein) and/or maize grain (glucogenic energy and oil) were added to the diet.



Fish meal (0.25kg/d)

Maize meal

( 1kg/d)

Fish meal + maize (0.25kg+1kg/d)

Bagasse intake (kg DM/d)





LW change (kg/d)





Feed conversion (kg DM/kg gain)





Source: Naidoo et al 1977

The data in Figure 8.8 show how the commercial feeding system was developed in Colombia, starting from the premise that the treated bagasse should con­tribute the major part of the diet and that locally available supplements should be used. The diet which gave the best results (810g/d of liveweight gain), and which was chosen for the commercial programme, contained (% dry matter basis): 53 steamed bagasse, 16 final molasses, 2 urea, 15 gliricidia foliage, 6 poultry litter, 7 rice polishings and 1 salt.

Figure 8.8: Development of a cattle feeding system based on hydrolysed cane bagasse (steam at 14kg/cm2 for 5 minutes). The same 8 groups of animals (weaned bulls of 180kg initial liveweight) were used throughout the twelve month trial. In phases 1 and 2, the basal diet was treated bagasse pith supplemented daily with molasses/urea (10% urea), gliricidia foliage (2% of liveweight daily) and poultry litter (0.2% of liveweight). The variable was the presence or absence of rice polishings (0.2% of liveweight, RP). In phase 3 the treatments were untreated bagasse and bagasse pith, with or without the rice polishings. In phase 4 the effect of additional long fibre was studied (from African Star grass S G) with the basal diet using treated bagasse and with the addition of rice polishings. In phase 5, all the animals were given the best diet based on the results obtained in the previous phases (Source: Preston 1987).


The molasses was used as a carrier for urea and also provided trace elements; gliricidia foliage was the source of fibre, vitamin A and some fermentable and bypass protein; poultry litter provided fermentable N and macro (Ca, P, S) and micro (Cu, Co, Zn etc) minerals and rice polishings was the source of nutri­ents which improved the balance of amino acids and glucose available in the total nutrients absorbed and this increased the efficiency of feed utilisation. The lipid content of rice polishings was expected to be used highly efficiently in this otherwise low fat diet.



Elephant (or Napier or King) grass (Pennisetum pur­pureum), guinea grass (Panicum maximum) and sugarcane (Saccharum officina rum ) are among the high­est yielding perennial crops, in terms of total biomass production per unit area and efficiency of solar en­ergy capture. Pennisetum species and sugarcane are used widely in the American tropics as a reserve crop ("ensilaje vivo") for feeding during the dry season. Sugarcane has the advantage that its energy value as feed increases as it matures, since the accumulation of sucrose more than compensates for the increasing lignification of the cell wall. The "stress" of the dry season (low soil moisture, low soil N and [generally] lower air temperatures) also stimulates the storage of sucrose in the stem.


Pennisetum yields most biomass when it is har­vested at 6-month intervals (Figure 8.9), although it is well understood that nutritive value is highest when harvesting is over shorter intervals (about 6 weeks). On the farm, it is difficult to maintain the rigorous practice of fertiliser application, irrigation and fre­quent cutting and as a result the N content and dry matter digestibility of the infrequently harvested for­age are low.


Figure 8.9: Annual biomass yields from sugar cane and elephant. grass harvested at different intervals (Source: Alexander et al. 1979)

Early work with these forages emphasised their use as "roughage" supplements in concentrate diets for intensively managed (usually confined) milking and fattening cattle and buffaloes. This policy predicated against the efficient use of these feed resources since the drop in rumen pH when cereal grain is fed depresses the digestion of fibre (see 0rskov and Frazer 1975).

In the following section examples are given of re­cent research in which these forages have been the basis of the diet and have been strategically supple­mented.
8.3.1 Legume forages

In Costa Rica , lactating goats were fed a basal diet of King grass (Pennisetum purpureum) supplemented with a fixed allowance of green banana fruit and in­creasing amounts of the leaves of the legume tree Erythrina poeppigiana. Total dry matter intake and milk production increased linearly with legume sup­plementation (Figure 8.10). There was only a mini­mal substitution of the King grass in the diet (intake fell from 690 to 600g dry matter / day).

Figure 8.10: Effect on dry matter intake and milk yield of goats of supplementing their basal diet of King grass and banana fruit with foliage of Erythrina poep­pigiana (Preston 1987).

 In research in Colombia the foliage of the legume tree, Gliricidia sepium, was given as a supplement to weaned steers fed a basal diet of freshly har­vested King grass during the dry season (Figure 8.11). Growth rate increased curvilinearly in response to in­creasing levels of the legume foliage, with the opti­mum legume content of the diet being about 30%.

Figure 8.11: Effect of increasing levels of gliricidia foliage on the growth rate of weaned bulls (initial weight 180kg; 4 animals per group) given a basal diet of King grass (Source: ILCA 1986/87, cited by Preston 1987)
Similar effects have been reported with West African Dwarf goats in Nigeria fed combinations of Guinea grass (Panicum maximum) and gliricidia (M. van Houtert, personal communication).


Table 8.13: Effect of supplements of leaves from Gli­ricidia maculata on performance of gl'owing sheep fed a basal diet of Brachiaria mileformis.

Feeding a supplement of gliricidia to growing sheep on a basal diet of freshly harvested Brachiaria multi­formis gave a significant response in bodyweight gain and in wool growth when the legume comprised up to 28% of the diet (Table 8.13).


Table 8.13: Effect of supplements of leaves from Gli­ricidia maculata on performance of growing sheep fed a basal diet of Brachiaria mileformis.


% Gliricidia in diet (DM basis)






LW gain, g/d





DM intake,






DM conversion





Carcass, kg





Clean fleece, g





Staple length, cm





Source: Kantharayu and Chadhakar 1981


Results of studies with milking cows fed diets based on freshly harvested Setaria grass and given a range of supplements are shown in Table 8.14. The most appropriate supplement was groundnut cake since it maintained body weight and supported the same lev­els of milk production in cows as cereal grain or molasses-based supplements fed at twice the rate. The implication is that the principal deficiency in the absorbed nutrients was amino acids and this was effectively corrected by the ground nut supplement, which provided bypass protein.


Table 8.14: Effects of supplements based on molasses, cereal brans/oil cake or groundnut cake on milk yield and liveweight change of Friesian cows given a basal diet of freshly harvested grass (Setaria kazangula) ad libi­tum.


No suppl.

Cereal/oil cake


Groundnut cake

Milk yield, kg/d*





LW change, kg/d





Mapoon et al 1977
*Corrected for milk yield on standard diet before and after the experimental period


8.4 Sugar cane

Growing sugarcane, more than any other crop, max­imises the yield of biomass per unit area.  Sugarcane is an ideal crop to optimise biomass utilisation because:

There are a number of sugarcane byproducts that can be used in animal feeds. Details of the two princi­pal methods of extracting sucrose from sugarcane and the associated crop residues and resultant byprod­ucts are outlined in Figure 8.12. Of the two extrac­tion processes, the industrial technology produces the most byproducts, the principal one being molasses. In the artisan (small-scale) system for production of "Gur" (Indian continent) or "Panela" (Latin Amer­ica) there is no centrifugation and therefore no final molasses.


Figure 8.12: Residues and byproducts from the manufacture of sugar by "factor'y" and "artisan" methods. Numbers in brackets indicate approximate quantities (fresh basis) relative to cane stalk = 100. I
e: Preston 1983a).

8.4.2 Whole sugar cane
Urea supplementation

In all the trials discussed here, urea was added to the sugarcane at levels that would satisfy the needs of the rumen micro-organisms for fermentable nitro­gen (approximately 3% of the dry matter of the diet).


The optimum level was validated in an experiment in which urea concentrations were varied from zero to 4% of the sugarcane dry matter. All cattle were supplemented with rice polishings (l kg/day) and miner­als (Figure 8.13). All the parameters of animal per­formance increased curvilinearly with increasing urea in the diet.


Figure 8.13. The relationship between the level of urea in the diet and live weight gain, feed intake and feed conversion of cattle a diet of sugar cane and 1 kg/d of rice polishings (Alvarez and Preston 1976b)


When rice polishings were absent from the diet, sugarcane intake remained low and the animals lost weight irrespective of urea level; the only positive re­sponse was in digestibility (Ferreiro et al. 1977).


Cattle growth rates and feed conversions were sim­ilar when a urea solution was sprayed on to the cane (as an aqueous solution or in dilute molasses), or was given in a separate feeder as concentrated (10%) so­lution in molasses.

Foliage from food crops and legume trees

Cassava tops and leucaena forage given as supple­ments to cattle fed ad libitum chopped whole sugar­cane plus urea, increased the cattle's voluntary intake of the total diet but reduced the intake of sugarcane (Meyreles et al. 1977; Hulman and Preston 1981); improvements in growth rate were small (from -40 to +140g/day with cassava as the principal supplement; and from 60 to 200g/day when leucaena was fed).


A supplement of sweet-potato foliage added to a basal diet of chopped sugarcane and urea did not depress intake of the cane and increased total dry matter consumption by 34% (Meyreles and Preston 1978a). Liveweight gain was not measured in this trial but significant improvements in liveweight gain of cat tIe were observed when this forage was added to a ration of derinded cane stalk (cane pith) (see Figure 8.18) This indicates that the foliage of sweet-potato is one of the most suitable "protein-rich" forages to use with sugarcane. The reason may be its higher rate of degradability in the rumen compared with ei­ther cassava or leucaena forage (Santana and Hovell 1979a, b), which results in a low rumen "load" while at the same time it stimulates rumen function.


Fresh banana leaves, which are only slowly digested in the rumen, were particularly unsuitable as a sup­plement as they reduced the intake of sugarcane and resulted in a lower total dry-matter intake (Meyreles and Preston 1978b).


A comprehensive series of experiments with sugar­cane as a basal feed for cattle was carried out in Mexico and the Dominican Republic with the aim of understanding the constraints associated with feeding this crop as the basis of the diet for growing/fattening and lactating cattle (Preston and Leng 1978a,b).


The supplement that promoted the highest level of productivity was rice polishings given at a level of 10­15% of the diet dry matter (Figure 8.14 and Figure 8.15). Similar conclusions were reported by Creek et al. (1976), who fed diets of 59% sugarcane (dry­matter basis) supplemented with rice polishings and cottonseed meal to Boran (Zebu) cattle in Kenya.


Figure 8.14: Effects of supplementation with rice polishings (which supplies bypass protein, bypass starch and oil) on growth rates of Zebu bulls in Mexico fat­tened on basal diets of whole sugarcane which has been chopped or derinded by the "Tilby" separator process (Source: Preston et al. 1976).
Figure 8.15: Effect of level of rice polishings supplementation on performance of cattle given free access to chopped sugar'cane and molasses containing 10% Urea (Lopez et al. 1976).


Rice polishings are relatively rich in protein(amino acids), lipid and starch, which are the critical nutri­ents that need to be adsorbed where the basal feed is digested solely by rumen fermentation. Experiments with cattle fitted with duodenal cannulae showed that the greater part of the starch (broken grain) in the rice polishings bypassed rumen fermentation (Elliott et al. 1978a); the amounts of microbial and dietary non-ammonia nitrogen arriving at the duodenum also increased in direct proportion to the amount of rice polishings in the diet (Elliott et al. 1978b) indicat­ing that rumen bacterial growth was stimulated and also that protein in rice polishings was protected from rumen fermentation.


The development of a sugarcane-based feeding sys­tem for dual purpose (Brown Swiss x Zebu) cows and their calves was described by Alvarez and Preston (1976b) and Alvarez et al. (1977, 1978). Best re­sults were obtained with combined supplementation of 500g of rice polishings per day and restricted graz­ing (3 hours/day) on a leucaena "protein bank" (Avarez et al. 1978). Complete substitution of leucaena for the rice polishings led to lower milk yields and loss of bodyweight in the cows which was attributed to mimosine toxicity (Alvarez and Preston 1976a) but may have been also a result of a lower fat intake.


Sugarcane tops are the traditional feed for draught animals (cattle, buffaloes and mules) employed in the harvesting of cane and its transport to the sugar mill (see Table 8.15). The utilisation of cane tops by work­ing animals has apparently not been studied. Cattle appear to maintain bodyweight while carrying out quite arduous work on a diet of only sugarcane tops. It appears that fermentative digestion of cane tops in the rumen provides an adequate balance of nu­trients for maintaining bodyweight when the energy (acetate) available (relative to protein) is reduced by work (see Chapter 4). Implicit in this statement is the concept that work increases feed intake.


Table 8.15: Composition of sugarcane tops and of the rind and pith fractions produced by the "Tilby" pro­cess.





Dry matter (DM) (%)




Composition (% DM)




Protein (N x 6.25)




Ether extract




Total sugars
















Source: Ministry of Agriculture, Mauritius


The apparent high nutritive value of cane tops for draught animals contrasts with their inability to sup­port growth in young animals without supplementa­tion. The data summarised in Figure 8.16 show that cane tops support high growth rates of cattle only when appropriately supplemented. Growing Zebu steers given a basal diet of chopped sugarcane tops grew at almost 700g daily when this feed was supplmented with urea and 1kg of rice polishings per day. Liveweight gain was the same on chopped cane tops as on chopped cane stalk. However, feed utilisation efficiency was higher on the cane stalk, apparently because of its higher content of solu ble sugars, which could have led to a larger proportion of propionate in the rumen VFAs (see Chapter 4).

Figure 8.16: In a fattening diet f01' cattle, increasing the proportion of cane tops (replacing chopped cane stalk) led to increases in feed intake and liveweight gain but a deterioration in feed conversion efficiency. The basal diet was supplemented with urea and 1 kg of rice polishings/day. Source: Ferreiro and Pre-ston 1976)


The constraints to the wider use of sugarcane tops in livestock feeding are the economics of harvesting and transporting the voluminous material. Tradi­tionally, sugarcane tops have been collected by small­holder farmers using draught animals, and even as "head loads". The increasing practice of burning the cane prior to mechanical, and even hand harvesting has reduced considerably the quantity of cane tops available.

Cane tops are one of the most under-utilised re­sources even in those countries in which shortages of animal feed and of fuel are most evident. When they

are fed to livestock, however, they have generally been used inefficiently because of the lack of knowl­edge of the need for "key" supplements. If they could be treated safely (and economically) to increase fibre digestibility this would improve their feeding value. Urea-ensiling has been effective in this respec.t (A. Boodo, unpublished).

In the late 1960s a technology (Tilby Separator Process-Figure 8.17) was developed for separating the cane rind from the pith. The aim was to use the cane rind in the manufacture of compressed boards which could substitute for plywoods that are usually imported into tropical countries. The residual pith was to be used for sugar extraction or alcohol production or as a feed for livestock.

Figure 8.17: Simplified diagram of the Tilby separator process for derinding sugarcane. (Source: Lipinsky and Kresovich 1982).

In early experiments carried out by Donefer and his colleagues in Barbados (see Pigden 1972), high rates of growth were observed in cattle fed sugarcane pith when it was supplemented with chopped cane tops and a concentrate containing an oilseed meal and urea. Unfortunately, these promising developments have not led to commercial application. The main limitation is the need for sophisticated and expen­sive machinery, necessitating a large-scale plant for economic viability. A factory producing compressed board would need a production capacity of about 30 tonnes of board per day, requiring the processing of 400 tonnes of sugarcane stalks. This would produce about 300 tonnes of pith per day-enough to feed 15,000 head of cattle .. While this size of unit is not unusual by feedlot standards in the USA, it is quite impractical for most developing countries, where the use of sugarcane as an animal feed has most potential.


A second constraint which emerged from research in Mexico (Preston et al. 1976) w