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Chapter 8

FEEDING SYSTEMS: STRAWS AND AGRO-INDUSTRIAL BYPRODUCTS

 

8.1 FIBROUS CROP RESIDUES

8.1.1 Factors influencing nutritive value
Introduction

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

Wheat

28-58

0.4-1.0

Oat

34-68

0.4-1.0

Rice

40-52

0.5-1.0

Barley

34-61

0.4-1.0

Maize

31-50

0.5-1.2

Sorghum leaves

65-78

0.5-0.8

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)

Leaf

70 (62-79)

6.0 (4.7-7.1)

Stem

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Source: J D Reed, unpublished data.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

NH3­straw

Straw intake (g/d)

 

 

Local

-

-

Crossbred

5.2

10.2

LWt change (g/d)

 

 

Local

-87

49

Crossbred

-211

168

Milk yield (kg/98 days)

 

 

Local

54

204

Crossbred

165

255

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.

 

Concentrate*

Azolla**

LWt gain (g/d)

140

330

Feed intake (kg DM/d)

 

 

Wheat straw+sugarcane tops

 

 

Supplement

 

 

Total

3.6

3.0

Feed conversion

(kg DM/kg gain)

26

9

OMD (%)

45

59

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

 

-LF

+LF

-LF

+LF

DM intake, kg/d

5.1

6.6

3.6

3.9

DM digestion,

38

42

47

48

N retention, /d

-6

+7

-6

+26

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.

 

 

Urea

Formal-C

RSM

Formal-RSM

SFM

Formal-SFM

DM intake (g/d)

1316

1779

1750

1899

1909

1977

Digestibility (%)

 

 

 

 

 

 

OM

45

50

48

46

48

46

NDF

40

47

45

45

44

45

LWt change (g/d)

30

132

'140

144

144

157

Wool growth (g/d)

4.5

11.0

10.5

10.1

10.1

11

Source:

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

 

1

2

3

Feed intake (kg/d)

 

 

 

Rice straw

5.81

6.22

4.35

Supplement

0.87

1.74

2.62

Total

6.68

7.96

6.97

LWt gain (kg/d)

0.47

0.84

0.93

Feed conversion

 

 

 

(kg DM/kg gain)

14

9

7.5

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
(g
/d)

None

0

38

 

0.4

365

 

0.8

292

 

1.2

306

Treated with 3% NH3 gas

0

236

 

0.4

497

 

0.8

601

 

1.2

639

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)

 

Straw

NH3­straw

Straw

NH3­straw

Cow1

1.1

2.3

-149

+109

Cow2

2.4 (4.6)

3.4 (4.9)

-266

+93

Buffalo3

2.4 (6.8)

3.2(7.6)

-17

+93

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.
F
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

 

Straw

NH3 straw

Concentrate (% diet DM)

Zebu x Friesian

11

8

Zebu

21

14

Buffalo

11

5

Milk produced (kg/kg concentrate)

Zebu x Friesian

1. 7

2.7

Zebu

2.8

4.2

Buffalo

                   4.0                           

6.0

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

 

0

1

Milk yield (kg/d)

2.6

3.2

Fat (%)

9.1

9.8

LW gain (kg/d)

0.1

0.21

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.

 

8.2  FIBROUS AGRO-INDUSTRIAL BYPRODUCTS

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.

 

Control

Fish meal (0.25kg/d)

Maize meal

( 1kg/d)

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

Bagasse intake (kg DM/d)

4.0

4.4

4.5

4.5

LW change (kg/d)

-0.17

+0.08

+0.16

+0.33

Feed conversion (kg DM/kg gain)

-

34

23

12

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.

 

8.3       FRESHLY HARVESTED GRASSES

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)

 

0

28

50

65

LW gain, g/d

25

43

44

39

DM intake,
 g/d

530

610

690

690

 

DM conversion

21

14

16

18

Carcass, kg

10

12

12

12

Clean fleece, g

280

350

320

360

Staple length, cm

4.3

4.7

5.4

5.5

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

Molasses/urea

Groundnut cake

Milk yield, kg/d*

6.1

7.6

6.8

7.9

LW change, kg/d

-0.72

0.0

-0.83

0.13

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
Sourc
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.

 

Pith

Rind

 

Dry matter (DM) (%)

22

39

27

Composition (% DM)

 

 

 

Protein (N x 6.25)

1.4

3.2

2.7

Ether extract

0.2

1.0

0.8

Total sugars

46

24

27

Fibre

45

70

57

Ash

1.9

3.1

5.3

Sulphur

0.2

0.3

0.4

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) was the realisation that, as a feed for cattle, the pith was little better than the chopped whole sugarcane plant when both were adequately supplemented, even though sugar­cane pith contains a higher concentration of soluble sugars than chopped whole cane (Table 8.15) and thus has a potentially greater feed value. In fact when it was supplemented with rice polishings (providing bypass protein, starch and oil) at low levels, the whole sugarcane supported higher growth rates than the derinded stalk. Only at the highest level of supplementation was there an indication that ani­mal productivity was higher on a basal diet of pith. Nevertheless, differences were relatively small (Fig­ure 8.15). These data indicate that it is the com­position of the supplement which determines animal productivity rather than minor variations in the ratio of sugar to fibre in the basal diet.

 

Meyreles et al. (1979) demonstrated that there is potential for exploiting the higher energy value of the pith by rational supplementation (Figure 8.18). In the absence of supplements other than urea and minerals, animals did not grow on a diet of sugar­cane pith. When green foliage of sweet potato was added to the diet, however, growth rate increased to about 500g/day and there was a significant re­sponse to high levels of urea (400 to 600g/ day). This can be interpreted as indicating an increase in micro­bial growth in response to an improved rumen microbial ecosystem, which. may be due to the supply of both readily digestible,fibre and essential nutrients for micro-organisms (eg.amino acids, peptides, min­erals and, perhaps, vitamins): Supplementation with cottonseed meal gave a similar growth response, but apparently without stimulating rumen function be­cause feeding the higher level of urea had no effect on growth rate. The combination of these supple­ments was additive and feeding the high level of urea appeared to stimulate rumen microbial growth, as in­dicated by the 60% increase in growth rate (Figure 8.18).

 

Figure 8.21: In a cattle fattening diet based on ad libitum molasses, sugarcane tops and wheat bran (1 kg/d), urea was a more effective source of fer­mentable-N than poultry litter'. Poultry litter stimu­lated growth rate when added to the diet (with Urea), which was appar'ently adequate in fermentable-N (Sourcee: Meyreles and Preston 1982).

 

Despite the possible advantages of using sugarcane pith rather than whole-cane, in some instances, the technology needed for chopping the whole sugarcane plant is simpler and much less sensitive to economies of scale than the derinding process. Chopping is therefore the preferred system for processing sugar­cane as a ruminant feed in developing countries.

8.4.5 Final molasses
Alternative uses of molasses as animal feed or for power ethanol

Molasses is the only "concentrated" source of fer­mentable carbohydrate that is widely available in the tropics and which is not a staple of the human diet. Its importance as a livestock feed is indicated by the ways in which it can be used:

Molasses is traditionally used to manufacture potable alcohol (eg. rum). However, since the oil crisis enormous efforts have been made to develop production of industrial alcohol, especially as a sub­stitute for gasoline (power-alcohol). The lack of tech­nical knowledge of how to use molasses efficiently in livestock feeds has resulted in much molasses being discarded. Often molasses accumulates in the storage tanks at the sugar mills and is discarded into rivers. Its opportunity cost is thus very low, which has been a principal argument for its use in power-ethanol pro­duction. However, the recent developments in the use of molasses in livestock feeding have given profitable alternatives that are vastly superior economically to the production of power alcohol (Table 8.16).

 

Table 8.16: Molasses may have a higher economic value when used as an animal feed than when it is converted into power alcohol

 

Opportunity cost $/t

Assumption

Survival feeding of cattle in drought

540

1

Substitute for cereals

150

2

Fattening cattle

92

3

Supplementing crop residues/dry pastures for:

Milk production

440

4

Prevent body weight loss

47

5

Power alcohol

15

6

  1. To keep cattle alive for 6 months about 360~:g mo­lasses/urea (1 %) is required. The cost of a replace­ment animal is estimated at US$200. After sub­stituting the urea and distribution costs the value attributable to molasses is approximately $540 per tonne

  2. The value of molasses as a replacement for imported grain i .• estimated on the basis that it has a substitu­tion value of 75 % and assuming that imported grain is US$200/tonne (CIF)

  3. It is estimated that used as the basal diet (70% of the total feed) for fattening cattle 6kg molasses supplemented with 150g urea and 8kg fresh legume forage supports a daily liveweight gain of 750g. The urea cost.. $0.045, the forage US$0.46 and the liveweight gain is valued at US$0.87/kg

  4. The daily con.oumption of 500g of a molasses/urea block; (50% molaHes, 20% urea, 20% bran, 10% minerals) ha.. increased milk yield on a straw­based diet by lkg/day (milk is worth to the farmers US$0.20/kg

  5. A daily intake of 1. 5kg of 8 % urea/molasses mixture prevents a weight 10H in cattle of 200g/day and that this weight 10H costs US$0.50/kg

  6. 4kg molasses are fermented to produce 1 litre of an­hydrous alcohol. Costs that are not included are the fuel for distillation and the interest/depreciation on the investment in a distillery. A barrel of oil (CIF) is assumed /,0 be worth $15.

 

There is an extremely strong argument for retain­ing molasses as a livestock feed in countries that suffer dry seasons and periodic droughts. The opportunity cost of using molasses (which may be the only feed available) in drought regions in the tropics is related to the value of a live animal and the survival of subsis­tence farmers who are dependent on draught animals.

 

Molasses is used widely in compounded feeds in the industrialised countries, where it is used to improve the palatability and binding properties of pelleted feed as well as reducing dustiness. Only low concetrations (5-10%) are needed for this purpose; higher levels make mixing and pelleting difficult. Because the molasses comprises such a small proportion of the diet, no nutrient imbalance is apparent. In trop­ical countries the quantities of molasses available are large relative to other potential feed ingredients. In these situations molasses can be used in three ways:

Many attempts have been made to incorporate mo­lasses into relatively inert materials such as bagasse and bagacillo (the residue after extraction of the coarse fibres for paper and particle board manufac­ture) but the final product is of poorer feeding value than the original molasses and is more expensive due to the high cost of power for mixing.

Supplementation

Research was conducted in Cuba in the late six­ties aimed at developing livestock feeding systems in which molasses was the principal ingredient. At the outset it was decided that molasses should be fed in its original liquid state in order to reduce processing costs and to facilitate transport and storage.

 

The successful development of the high-molasses fattening system for cattle (Preston et al. 1967) eemplifies the use of the basic principles of ruminant digestion and metabolism as outlined in earlier chap­ters. These include optimising rumen fermentation by supplying fermentable N (urea) and some high­quality green forage and balancing the amount of pro­tein (amino acids) to VFA by supplementing with a bypass protein source.

 

The original system used forages such as ele­phant grass, pangola grass and sugarcane tops as the roughage source. The availability of forage was restricted to 0.8kg dry matter/100 kg liveweight to encourage the animal to consume large amounts of molasses. The urea level was set at 2.5% of the fresh weight of the molasses to provide a ratio of fermentable N to carbohydrate close to the theoreti­cal requirements of rumen micro-organisms. Sulphur supplementation was not required as sulphur diox­ide used in clarification of cane juice and the residual sulphur concentrated in the molasses.

 

In the widespread commercial application of the feeding system in Cuba, fish meal (Peruvian) was the bypass-protein supplement. The dramatic effect of this supplement in raising animal productivity on the molasses-based diet is shown in Figure 8.19.

Figure 8.19. Addition of fish mealk to a basal diet of ad libitum molasses-urea and restricted forage substantially improved growth rate and feed conversion of cattle in Cuba (Source: Preston and Willis 1974)

Subsequent developments in the use of molasses­based diets have been directed to the use of: (i) protein-rich forages that supplied much, and somtimes all, of the bypass protein as well as the roughage (Table 8.17 and Table 8.18); and (ii) supplementation with poultry litter (Figure 8.20 and Figure 8.21).

 

Table 8.17: Leucaena foliage was as effective as groundnut meal in supporting high growth rates in young Friesian bulls fed a diet based on mo­lasses/urea. The leucaena replaced both the forage (native grass) and the groundnut cake, and may thus have served as a combined source of protein and roughage

 

Leucaena
(
% LW/d)

Groundnut. Cake
 (
g/d)

LW gain
 (g
/d)

790

740

847

597

742

Feed conversion (kg/kg gain)

9

12

10

10

10

Molasses
(
% of diet)

79

68

62

73

53

Source: Hulman et al 1977

 

 

 

Table 8.18: The foliages of cassava or sweet potato was used as the l'oughage supplement in a mo­lasses-urea diet for fattening bulls in the presence or absence of a supplement of soyabean meal. With cas­sava supplementation there were no benefits from aditional protein indicating that it was a better source of bypass protein than sweet potato foliage.

Forage

Sweet potato foliage

Cassava foliage

Soybean meal (g/d)

0

400

0

400

LW gain, g/d)

650

850

850

870

Molasses (kg/d)

5

6

6

6

Forage (kg/d)

13

13

10

10

Source: Ffoulkes and Preston (1978b)


 
Figure 8.20: Contrasting effects of legume (leucaena foliage) and grass (sugarcane tops) as the roughage supplement in a diet based on ad libitum molasses/u1'ea with or without supplements of wheat bran (1kg/d) and/or poultry litter (1.5kg/d) (Source: Meyreles et al. 1982).

 

 

Figure 8.21: In a cattle fattening diet based on ad libitum molasses, sugarcane tops and wheat bran (1 kg/d), urea was a more effective source of fer­mentable-N than poultry litter'. Poultry litter stimu­lated growth rate when added to the diet (with Urea), which was appar'ently adequate in fermentable-N (Source: Meyreles and Preston 1982).

 

There is evidence that, on molasses-based diets, poultry litter influences the pattern of VFA forma­tion, increasing the proportion of propionate and de­creasing the proportion of butyrate (see Table 5.2). This would partly explain the improved growth rates and feed conversions associated with the use of poul­try litter in molasses-based diets (Figures 8.20 and 8.21; see also Meyreles 1984; Herrera 1984).

Commercial feeding systems based on molasses

The data m Tables 8.19 and 8.20 summarise the results obtained when the molasses fattening pro­gramme was used commercially in large-scale feedlots and under conditions of restricted grazing on State farms in Cuba.

 

Table 8.19: Production data from a commercial cattle feedlot (10,000 head) in Cuba during the years when a change was made from an ad libitum forage (Pan­gola grass) plus concentrate diet to one based on ad libitum molasses/urea and restricted forage and fish meal. The high losses due to emergency slaughter and mortality in the first year of high molasses feeding were due to molasses toxicity (cerebro-cortical necro­sis, see Preston and Willis 1974).

 

Forage
1969

Molasses-based

1970

1971

Total LW gain (kg/d)

3,724

8,295

13,797

LW gain (g/head/d)

430

880

890

Feed conversion
(kg DM
/kg gain)

15

11

10

Deaths (%)

0.1

1.0

0.2

Emergency slaughter (%)

0.1

1.0

0.2

Source: Munoz et al. (1970).

 

Table 8.20: Performance of bulls fattened commer­cially in Cuba on ad libitum molasses/urea, fish meal and restricted grazing (3 hours/ day). Results are for 11 units each with 400 animals

 

LW gain
(kg/d)

Conversion (kg/kg LW gain)

Molasses

Fish meal

Urea

Worst

0.74

14.7

0.54

0.47

Mean

0.83

9.1

0.45

0.29

Best

1.04

5.9

0.32

0.19

Source: Morciego et al 1970

8.4.6     Metabolic disorders on molasses-feeding systems

Three metabolic disorders may occur in cattle and sheep fed diets containing more than 50% molasses:

Urea toxicity

This is discussed since, when high levels of molasses are used, urea is almost invariably included in the mo­lasses, and urea intakes may be as high as 300g/ day (eg. in a 500kg dairy cow consuming 10kg of the molasses/urea mixture per day).

 

However, there is little risk of urea toxicity since the sugars in molasses and ammonia from urea are quickly used in rumen microbial cell growth. Animals that have not previously consumed urea can be safely permitted free access to molasses containing up to 3% urea without fear of toxicity. Toxicity will only occur if the urea is not uniformly distributed, or mistakes have been made in formulation.

Molasses toxicity

This is probably the most serious problem associated with molasses feeding. For example, in the first year following the introduction of the molasses/urea fattening system in Cuba, mortality and emergency slaughter rates in a 10,000 head feedlot increased from 0.1 % and 0.4% (when a forage-based diet was fed) to 1% and 3% respectively, when the diet was changed to high levels of molasses/urea (see Table 8.19).

 

Cattle suffering from molasses toxicity salivate, stand apart in a "dejected" posture, usually with their heads lowered; and frequently are found "leaning" against the fence or feed trough. Invariably, eye-esight is affected and often the animal is blind. When disturbed they have an unsteady and uncoordinated gait and this led the "cowboys" in Cuba to refer to the affected animal as "borracho" (ie. drunk!!).

 

The nervous symptoms and blindness that were a feature of molasses toxicity indicated damage to the brain and it was subsequently shown by Verdura and Zamora (1970) that the clinical syndrome was indistinguishable from that of cerebro-cortical necrosis (CCN) also known as polioencephalomalacia (Edwin et al. 1979). The necrosis in the brain is readily seen and this allows rapid diagnosis.

 

The cause of the necrosis is likely to be a decrease in the energy supply to the brain because of either an absolute deficiency of alimentary thiamine, binding of thiamine analogues produced in the rumen and/or through the action of thiaminase in the rumen (Edwin et al. 1979), or a deficiency of glucose (Losada and Preston 1973). The evidence for the last explanation is that rumen propionate levels were extremely low (less than 10% molar) when the disease was induced in cattle deprived of forage (Losada and Preston 1973), and that daily oral administration of 400g of glycerol (a glucogenic substance frequently used in the treatment of ketosis) prevented clinical symptoms of the disease (Gaytan et al. 1977). In contrast, administering thiamine either intra-ruminally or intra-amuscularly did not prevent the disease (Losada et al, 1971 ).

 

Recent work by Rowe et al (1979a) introduced another element into the aetiology of molasses toxicity. They confirmed that removing the forage from a molasses-based diet induced symptoms of molasses toxicity, including brain necrosis, in which neither blood glucose level nor the rate of entry of glucose into blood was impaired. The most significant finding was that the absence of forage in the diet caused a rapid reduction in the rate of turnover of rumen fluid to the point of almost complete rumen stasis (from 1.5 to 0.5 volumes/day). Rowe et al. (1979a) hypothesized that, under these conditions, the supply of both amino acids and B-vitamins to the animal would be drastically reduced with a consequent decrease in the availability of thiamine for brain metabolism. Another explanation is that low rates of turnover of ru­men fluid might. encourage the proliferation of slow­-growing bacteria that produce thiaminase.

 

It is apparent that a number of factors interact in the development of molasses toxicity (see Figure 8.22). The basic defect common to all situations is the disruption of energy supply to the brain. This could be brought about by inadequacies in the ab­solute supply of blood glucose or thiamine (required for brain metabolism of glucose) or both, as well as by the action of thiaminases present in the feed or produced by the rumen microorganisms.

 

Figure 8.22: A summary of some factors that may affect the supply of blood glucose and its utilisation by the brain (Source: Rowe al. 1979a).

 

The theory that glucose deficiency is the main cause of molasses toxicity seems the most plausi­ble. The availability of glucose to cattle on molasses­based diets is always precariously balanced because of the low-propionate/high-butyrate fermentation of molasses, and t.he economic pressure to mini mise true-protein inputs. Molasses toxicity does not ap­parently occur in sheep. Sheep fed such diets have higher propionate fermentation patterns than c.attle which lends support to the concept of glucose being primarily involved in the syndrome. Removal of foage from a molasses-based diet givell to sheep does not result in the same rumen stasis as in cattle (Beeridge and Leng 1978).

 

Two processes may separately, or in combination, lead to excessive use of glucose and a lowering of blood glucose concentrations, which could lead to brain damage. These are:

This thesis is supported by observations of periods of low blood glucose levels in cattle during experi­ments which involved intensive blood sampling (R A Leng and M H Ferreiro, unpublished; also Gaytan et al. 1977).

 

When feeding high-molasses diets to cattle it is usual to restrict the supply of forage, either to in­crease intake of molasses or because of the greater cost of forage compared to molasses (see Table 8.20).

 

Inadequacies in either the quantity or quality of forage appear to be the main causes of molasses toxi­city. Thus, the incidence of molasses toxicity was less when wheat or barley straw, rather than sorghum for­age or maize silage, were used as the forage sources in molasses-based diets. Furthermore, there have been no reports of toxicity when high-protein forages (eg. leucaena and cassava alld sweet-potato tops) have been used. Equally, feeding nutritious and palatable forage appears to be the best cure for affected animals (T R Preston, unpublished data) .

 

Recent developments in the molasses-feeding sys­tem have emphasised the technical and economic ad­vantages of feeding high-protein forages, especially

from leguminous plants such as leucaena, as a com­bined source of both roughage and bypass protein. Including such forages in the diet is also likely to of­fer the most cost-effective means of avoiding molasses toxicity.

Bloat

Bloat is the retention in the rumen of gas, either free or trapped in foam, and occurs in cattle on almost all feeding systems. It is more prevalent with some diets (eg. grazed legumes that contain high levels of soluble foaming agents such as saponins and proteins). It is not a partic.ularly serious problem with molasses feeding. However, relatively high incidence of bloat (up to 5%) has been reported where access to the molasses is occasionally limited (eg. grazing cattle allowed access to molasses/urea only once or twice daily) and where cattle have eaten relatively large quantities of molasses/urea over short periods.

A hypothesis for the aetiology of the syndrome is as follows. In animals fed molasses-based diets, an organism grows in the rumen which produces consid­erable mucilaginous secretions (Methanosarcina bakerii -- see Rowe et al. 1979b) and which can reach high population densities. When the animals con­sume molasses quickly, the rate of fermentation in the rumen is high (producing considerable quantities of carbon dioxide and methane), the pH falls and the bicar bonate in the rumen fluid is converted to CO2. The very rapid production of gas in the presence of the mucilagenous organism forms a foamy bloat. A similar train of events is reported to cause feedlot bloat on grain-based diets (Cheng et aI. 1975). An optimum level of rumen ammonia accelerates fermen­tation and therefore bloat may be controlled by using a source of NPN that releases ammonia more slowly than urea, eg: chicken litter.

8.4.7 Sugar cane juice

The extremely low fermentability of sugarcane fibre (Figure 8.23) and the negative effect this had on vol­untary intake of the overall diet was the reason for developing methods for fractionating the crop so that sugar and fibre could be treated as separate entities.

 

 

Figure 8.23: Rate of loss of dry matter from ny­lon bags containing washed sugarcane fibl'e, pangola grass or a sample of hay grown in Scotland, suspended in the rumen of a steer fed a sugarcane-based diet (Source: Fernandez and Hovell1978).

The new approach to fractionation of sugarcane for livestock feeding and fuel production was first deveoped in Mexico (Preston 1980b). The aim was to achieve only partial extraction of the juice using sim­ple low-cost cane crushers, of the kind developed for "panda" and "gur" production. This reduced the investment in machinery and the energy cost of milling (stalks are passed only once through the crusher).

 

The justification for this system was that the juice is a suitable carbohydrate resource for both ruminant and non-ruminant livestock. The residual sugar-rich fibre can be gasified to make "producer gas" to sub­stitute for gasoline and diesel oil (T R Preston and A Lindgren, unpublished data). Alternatively it can be used as a component of the diet of draught animals or small ruminants that can readily select the pith from the rind (Preston 1987).

Supplementation

The fermentable carbohydrates in sugarcane juice and molasses are sucrose, glucose and fructose. Mo­lasses is the concentrated soluble residues after ex­traction of the sucrose from cane juice. It is there­fore richer in minerals, organic acids and other soluble plant components than cane juice.

 

Diets based on cane juice support much higher lev­els of animal productivity than those based on mo­lasses. The rates of growth and feed conversion effi­ciency recorded in studies in Mexico (Table 8.21 and Figure 8.24) are comparable to those recorded in intensive grain-based systems.

 

Table 8.21: Holstein/Zebu bulls had higher· g1'Owth rates and better feed conversion on a basal diet of fresh sugarcane juice than on molasses. The differ­ence was especially marked in the absence of the by­pass protein supplement (sunflower seed meal SSM).

Basal diet

SSM supplement (kg/d)

LW gain
(g/d)

Intake of molasses/cane juice (kg/d)

Feed conversion (kg DM/ kg gain)

Molasses

0.0

250

4

26

 

1.0

550

4

12

Cane juice

0.0

800

23

7.4

 

1.0

1320

32

6.4

Source: Sanchez and Preston 1980

 

Figure 8.24: Zebu steers had high growth rates and efficient feed conversion on sugar cane juice supple­mented with ammonia and leucaena  foliage. Addi­tional bypass protein from fish meal increased growth rate slightly but there was no effect on feed conversion (Source: Duarte et al. (1982).

 

The potential for use of cane juice is considerable because microbial growth in the rumen on this feed appears to be highly efficient; Zebu cattle grew at 800g per day on minimal protein intake (5% protein in the diet dry matter supplied from leucaena) with the fermentable N provided by aqueous ammonia. This is in contrast to the average grain-based feeding system, in which at least 12% of the diet dry matter is protein. It appears that on a cane juice diet, the end-products of rumen fermentation are better bal­anced and therefore support much higher levels of aimal productivity than sugarcane pith. This indicates that microbial growth in the rumen was extremely efficient since it must have supplied an almost ideal protein/energy ratio for production without supple­mentation.

 

Two observations on feeding cane juice to cattIe are pertinent to the underlying thesis of this book:

The importance of these factors as determinants of efficient ruminant productivity are discussed in Chap­ter 5.

 

Figure 8.25: There were higher molar proportion of propionic acid and lower proportion of butyric acid in rumen fluid of cattle fed sugarcane juice than with cattle fed molasses (Source: Perez et al. 1981).
8.4.8 Residual pressed cane stalk

The maximum economic benefit from the use of sug­arcane juice for livestoc.k feeding will only be re­alised iftechnologies are developed to use the residual pressed stalk. The options being pursued for the use of this material include:

Making charcoal from pressed cane stalk is simple but requires briquetting to produce a readily saleable product (Ffoulkes et al. 1980).

 

To be able to use pressed cane stalk for producer­gas production, it must first be sun dried to 20% moisture content and chipped into particles of 10 to 20mm in length. A gasifier has been designed that uses dried sugarcane chips (A Lindgren, personal communication) .

 

A promising development is the potential of using the pressed (extracted) cane stalk as a basal diet for small ruminants. When it is available immediately following juice extraction, goats eat it avidly, selecting the sugar-rich pith and rejecting the lignified rind. In studies in Colombia, goats on a mixed diet of pressed stalk and fresh gliricidia foliage selected, and apparently preferred, the pith to the green foliage (Preston 1987).

8.5 Sisal bagasse and pulp

8.5.1 Introduction

Sisal (Agave fourcroydes) is a source of fibre for twine, ropes and carpets. The entire leaf blade is harvested and transported to the factory, and there are thus no residues in the field. However, the bagasse that remains after the fibres are extracted is potentially useful. The bagasse left after traditional processing contains both long and short fibres. More advanced factories extract a greater proportion of the fibres and some of the saponins, which are used as raw ma­terial for the manufacture of steroid hormones. The byproduct of this modified process is referred to as "pulp" to differentiate it from bagasse (Riley 1984).

 

Data on the chemical composition of both these byproducts are given in Table 8.22. Because of the high content of soluble sugars and the high moisture content, the pulp or bagasse begins to ferment immdiately after fibre extraction and most of the soluble sugars are converted to lactic acid.

 

Table 8.22: The chemical composition of sisal bagasse and pulp

 

 

Sisal pulp

Sisal bagasse

 

 

Fresh

Ensiled

Fresh

Ensiled

Fresh

Proximate analysis (% DM)

 

 

 

 

 

Crude fibre

 

29

30

28

29

23

Crude protein

 

      5.3

4.9

5.3

5.5

6.3

Ether extract

 

     3.1

3.0

3.7

3.4

3.0

Ash

 

 

13

13

15

15

12

Water-soluble  CHO

21

0

27

0

 

Mac1'O-minerals (g/kg DM)

 

 

 

 

 

Calcium

 

51

53

47

49

35

Phosphorus

 

1.1

1.0

1.0

1.2

1.5

Magnesium

 

8.0

8.0

9.0

10.0

8

Trace minerals (mg/kg DM)

 

 

 

 

 

Zinc

 

 

1.2

1.2

1.5

1.4

 

Copper

 

 

0.5

0.5

1.0

0.8

 

Cobalt

 

 

ND

ND

ND

ND

 

Manganese

 

1.0

1.1

1.0

0.8

 

Iron

 

 

2.0

1.8

2.3

2.2

 

0rganic acids (% DM)

 

 

 

 

 

Lactic

 

 

1.6

16.5

1.0

18.1

 

Citric

 

 

1.0

0.5

1.2

0.8

 

Oxali,

 

 

5.5

5.3

5.2

5.4

 

pH

 

 

4.0

3.9

3.9

3.8

 

Source:

Harrison (1984).

 

 

 

 

 

 

The constraints associated with the use of the pulp/bagasse as a feed for ruminants relate partly to the content of organic acids, principally lactic and oxalic acids. Phosphorus and some of the trace elments are also severely deficient, and thus the min­erai content of pulp or bagasse is highly imbalanced relative to the needs of productive animals.

 

Cattle fed only on ensiled sisal pulp for a long priod developed acidosis and barely maintained bodweight, despite the reasonably high digestibility (50­60%) of the feed (Naseeven and Harrison 1981). Attempts to correct only the acidosis and the min­eral imbalance did not increase animal productiv­ity (Naseeven and Harrison 1981; Belmar and Riley 1984) .

 

Research in Mexico on the use of sisal pulp as a feed for ruminants (Rodriguez 1983) is a further ex­ample of the application of the principles developed in this book, namely that attention should first be given to optimising the rumen ecosystem and then to correcting the protein/energy ratio with bypass pro­tein (Chapter 7). Only after these two steps have been taken are responses to supplementary minerals observed (Figure 8.26).

 

Figure 8.26: Sisal pulp is relatively digestible (55-60%) but low in fennentable-N, protein and minerals. Supplementing with urea and mineTals had no effect on lamb performance until green forage (foliage from the tree Brosium alicastrum) and/or bypass protein (soybean meal) were also given (Source: Rodriguez 1983).
 

8.6 Bananas and plantains

Bananas and plantains provide voluminous amounts of crop residues which are normally incorporated into the soil for mulching and to maintain soil fertility. When bananas are grown for export, up to 20% of the fruit may be rejected, and these are often discarded.

There are few nutritional constraints to the use of banana fruit as feed for ruminants. However, it is important to feed the material while it is green and the carbohydrate is still in the form of starch. The fruit can be fed as a complete bunch (or "hand") and there is no need for any processing. The fruit is low in nitrogen and the skin is rich in tannins. The greatest nutrient deficiency of bananas as a feed for ruminants is fermentable nitrogen and diets contain­ing bananas must be supplemented with urea.

 

Where molasses is freely available, the most con­venient procedure for supplementing cattle with urea is to allow the cattle free access to a urea/molasses mixture (10% urea). Cattle will restrict their intake of this supplement to about 2kg/day, which provides enough urea (200g/day) to ensure an adequate level of ammonia in the rumen for efficient fermentation (McEvoy and Preston 1976). If a high-protein forage is fed with the diet, either as a legume component of a pasture in a restricted-grazing system or as a protein-rich foliage (eg. leucaena or gliricidia), there appears to be no advantage from supplementing with a bypass-protein meal. Results from feeding reject bananas to cattle in Colombia are summarised in Table 8.23.

 

Table 8.23: Growths rates of cattle fattened under commercial feedlot conditions in Colombia on reject bananas (40% of diet DM), chopped elephant grass (42%) and Kudzu legume forage (18%) with different supplements.

Protein suppl.

Initial LW
 (kg)

Daily gain (kg/d)

Days on feed

Comparisons

No supp!.

330

0.83

90

Female adult

 

325

0.64

90

Male adult

 

334

0.80

90

Female old

 

325

0.88

90

Female young

 

240

0.91

100

Male young

 

350

0.61

100

Male old

1kg/d CSC  

381

1.15

60

+ sulphur

 

391

0.97

60

- sulphur

 

332

0.98

60

Ureal

 

 

 

 

Jllolasses

 

322

0.97

60

Aqueous urea

2kg/d CSC

 

1.60

 

Chianina x Zebu

 

 

1.14

 

Zebu crosses

 

 

1.25

 

Zebu bulls

 

 

1.10

 

Zebu steers

 

 

1.66

 

Chianina bulls

 

 

1.50

 

Chianina steers

Source: Perex and Roldan 1984
CSC cotton­seed cake

8.6.2 Banana foliage

The dry matter in the leaves and pseudostem of the banana plant is relatively digestible (65 and 75%, respectively; Ffoulkes and Preston 1978a). Despite this, these feeds barely support maintenance if given alone to ruminants. However, when ruminants are fed banana pseudostem they respond to supplementation with urea, highly digestible green forage and bypass nutrients. The data in Figure 8.27 show that cat­tle increased their voluntary feed intake significantly when the chopped leaves and pseudostems were sup­plemented with sweet-potato foliage or with wheat bran. The highest feed intake was observed when both sweet-potato foliage and wheat bran were given together.

 

Figure 8.27: Supplements of wheat bran (1kg/d) and/or sweet potato tops (5% bodyweight, fresh basis) increased the voluntary feed intake of cattle given a basal diet of chopped banana pseudostcm, urea and minerals (Source:: Fernandez et al. 1981).

Feeding systems based on banana foliage have been developed in the Seychelle Islands (Figure 8.28). Ac­ceptable levels of growth were obtained in cattle fed the banana forage, urea and leucaena, and there was an apparent response to additional supplementation with banana fruit.

 

 

 

Figure 8.28: Growth performance of crossbred (Jerrsey/Creole) cattle in Seychelles fed a basal diet based on the whole banana plant (pseudostem and leaves plus urea and minerals) and supplements of fresh leuucaena foliage (3% bodyweight/d) alone or with some reject banana fruit (3kg/d) (M Delpeche and T R Preston, unpublished data).

 

Sugarcane produces enormous amounts of biomass. Picture shows sugarcane being chopped for feeding trials with cattle in Mexico (Alvarez F)
Crop residues are the major feed biomass for cattle 111 developing countries (China-Leng R A)

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