Chapter 7 Back to Contents

 

Chapter 7

GUIDELINES FOR FEEDING SYSTEMS

7.1 Introduction

In order to develop feeding systems information on the n u tri tional characteristics of feed resources must be related to the requirements for nutrients accord­ing to the purpose and productivity of the animals in question. In the industrialised countries, this in­formation has been incorporated in tables of feeding standards, which interpret chemical analyses of feed resources in terms of their capacity to supply the en­ergy, amino acids, vitamins and minerals required for a particular productive purpose. These standards are steadily becoming more sophisticated with the aims of improving their effectiveness in predicting rates of animal performance and to derive least-cost formula­tions.

7.1.1 Limitations to "conventional" feeding standards

The relevance of feeding standards for developing countries, particularly those in the tropics, has been questioned from the socio-economic standpoint (Jackson 1980). It has been apparent for many years that feeding standards based on assigned nutritive values (eg. net energy) are misleading when uncon­ventional feed resources are used (eg. Preston 1972; Leng and Preston 1976; Gaya et al. 1981), since the levels of produetion achieved may be consideably less than that predieted. More importantly, this often led to the rejection of many available feed re­sources which apparently were too low in digestible energy to supply the energy needed for production. It also encouraged researchers to copy feeding systems used in temperate countries which are relatively "pre­dictable", but which require feed resources that are inappropriate on socio-economic grounds in most de­veloping countries.

A new approach to the development of feeding sys­tems, not based on conventional "feeding standards" , is needed because:

In the early 1960s, Professor Max Kleiber ex­pressed a similar concern for these issues and stated that (as quoted by Kronfeld 1982):

To this could be added that the availability of these nutrients, and their interactions, affect the efficiency with which nutrients are used.

 

The misconceptions inherent in any system based primarily on feed analysis are that it is almost impossible to predict:

For these technical reasons, and also because of differing socioeconomic circumstances, it is proposed that a more appropriate objective for developing countries is to "match livestock production systems with the resources available" (Chapter 1).

 

This chapter sets out the guidelines for applying these concepts to the development of feeding systems that should make best use of locally available re­sources and which should be built on traditional prac­tices. Farming systems in developing countries are notoriously difficult to change and innovation must be introduced gradually without inducing excessive risk, which may directly affect the well-being of the family of a poor farmer.

 

This chapter aims to:

7.1.3     Animal response to non­conventional feed resources

Doubts concerning the usefulness of feeding stan­dards for ruminants in tropical countries surfaced during development work in Cuba (Preston and Willis 1974) in the 1970s when livestock produc­tion systems were being established using non­conventional feed resources (ie. diets containing a large proportion of molasses). This research demon­strated that small inputs of bypass protein (Peruvian fishmeal) dramatically increased growth rate and feed efficiency of cattle. However, because of the higher demand for critical nutrients by lactating animals,

high milk production could not be supported on di­ets in which molasses comprised a large proportion of the total feed intake (Figure 4.17) .

 

This work demonstrated the high potential yield of animal products from sugar-cane and stimulated re­search in Mexico, Mauritius and the Dominican Re­public that attempted to establish cattle production systems applying the principles developed for feeding molasses (high-sugar diet) (Preston et al. 1976).

 

Research on the feeding value of whole sugar-cane demonstrated that:

The implication of these two sets of findings is that rumen function did not provide the required balance of nutrients for productive purposes (Leng and Pre­ston 1976).

 

Recognition of the role of bypass protein in low-N diets led to research aimed at increasing productivity of cattle and sheep on a range of fibrous feeds (Leng et al. 1977). This is discussed in Chapters 8 and 9. Prior to this work these feeds were considered to have little value other than to support maintenance and were universally referred to as "low quality" fibrous feeds. It was generally believed that the only recourse was to improve their digestibility, in particular by alkali treatment (Jackson 1977, 1978).

 

The value of alkali treatment was obscured by the fail u re to recognise the fundamental importance of providing nutrients to create an efficient rumen ecosystem and to meet the animal's potential pro­ductivity (Leng 1982c; Preston and Leng 1984).

 

Combining alkali treatment and appropriate sup­plemen tation has led to practical feeding systems based on rice straw being applied on farms in Bangladesh (Dolberg et al. 1981; Davis et al. 1983) and Sri Lanka (Perdok et al. 1982; Jayasuriya 1984).

 

Alkali treatment of straws is a difficult operation for small farmers. However, development of princi­ples for supplementary feeding has led to significant improvements in the utilisation of straw as animal feed, particularly in India (see Leng and Preston 1984 and Chapter 11).

 

The importance of these developments was not so much the use of molasses or straw in animal feeding, since both have been incorporated into diets for rumi­nants in industrialised countries for many years, but in the magnitude of the contribution of molasses and straw to the total dietary dry matter. In industri­alised countries molasses and straw rarely comprise more than 10 to 15% of the diet, the rest of the ration being cereal grains, high-protein forage and oilseed cakes. In contrast, in developing countries the feed­ing regimes aim to incorporate molasses or straw as the principal component of the diet because they are available locally, and because the use of grain for live­stock feeding is restricted for financial, political and socioeconomlc reasons.

 

Animals fed diets based on sugar, straw or dry pas­tures have a much larger response to supplementation with small amounts of bypass protein than animals on a diet based on cereal grain (Table 7.1). However, even when these diets are supplemented with bypass protein, feed utilisation efficiency is lower than that obtained on diets of similar metabolisable energy cotent but with a large part of that energy contributed by cereal grain (Pigden 1972; Redferne and Creek 1972). The inefficiency with which energy is used ap­pears to be most pronounced when the host animal has a high demand for amino acids and glucose pre­cursors (eg. the lactating cow) (Clarke et al. 1972; Chopping et ai. 1970; Perdok et al. 1982).

 

There are many reasons why cattle when fed mo­lasses or straw as the main components of a diet are more responsive to supplementation and/or manip­ulation of the rumen when these ingredients are a small proportion of the diet. Some of these differ­ences can be explained on the basis of interactions and associated effects among nutrients and between nutrients and the site of digestion. These are dis­cussed in Chapters 3, 4 and 5.

 

Feeding standards are almost impossible to apply to the grazing animal because of selective grazing and the difficulties of estimating their intake of pasture.

7.1.4 Nutritive value

In order to accurately predict responses in productiv­ity to supplements with a particular diet, it is neces­sary to take account of the constraints to metabolism. These relate specifically to the protein, gluc.ogenic en­ergy, VFA energy and long-chain fatty acid (LCFA) energy in the end-products of fermentative and in­testinal digestion as a function of total metabolisable energy intake, since the balance of these determines the animal's productivity.

Productivity of ruminants is influenced primarily by feed intake, which in turn is determined by the digestibility of the feed and the capacity of the diet to supply the correct balance of nutrients required by animals in different productive states. Therefore the two major variables that need to be considered are:

The balance of nutrients available depends upon:

A t present it is not possible to predict nutrient re­quirements and to match these with the availability of nutrients because ofthe many interactions between the animal, its rumen microbial ecosystem and the diet.

 

Usually the most widely available and cheapest feeds for ruminants in most developing countries are crop residues and, to a lesser extent, agro-industrial byproducts and native pasture. Protein meals, de­rived from oilseed residues and the processing of an­imals, fish and cereal grains are expensive and often unavailable.

Table 7.1: Some selected examples of the effects of feeding a bypass-protein meal (EP) to sheep and cattle given different basal diets all supplemented with adequate amounts of fermentable-N

     

Growth rate (g/d)

 

Species

Bypass protein

  Basal diet

-BP

+BP

Author

Sheep

Fish meal

Barley grain

230

300

0rskov et al. (1970)

 

Fish meal

Sugar / chaff

0

180

Bird et al. ( 1979)

 

Pellets (1)

Barley straw

24

100

Bird et al. (1981)

Cattle

Fish meal

Molasses

270

1000

Preston & Willis (1974)

 

Fish meal

Cane juice

800

960

Duarte et al. (1981)

 

Fish meal

Straw/conc.

180

650

Smith et al. (1979)

 

 Fish meal

Ammoniated rice straw

100

400

Saadullah et al. (1982)

 

Cottonseed meal

Pasture

-320

220

Lindsay & Loxton (1981)

 1. Contained formaldehyde-treated cottonseed meal, meat meal and fish meal 

 

In general terms, energy (the basic feed resource) and fermentable N (urea) are relatively inexpesive ingredients, while the sources of amino acids and glucogenic compounds (the protein meals, ce­real grains and cereal byprod ucts) are very expensi ve. Since fermentation of carbohydrate provides the eergy for microbial growth, and as the feed is often of low digestibility, it is generally desirable to supply fermentable energy on an ad libitum basis. Therefore the basal diet should be freely available.

 

As a rule of thumb, 3 g of nitrogen are needed per 100 g offermentable carbohydrate to support efficient microbial growth. It is not always necessary to pro­vide this amount since some feed protein will be fer­mented to ammonia and some urea-N may enter the rumen in saliva. In addition there is evidence that the rumen microbes need small amounts of amino acids and other nutrients for efficient microbial growth.

 

The potential of the diet to satisfy the animal's re­quirements for amino acids and glucogenic precursors depends on the pattern of fermentation and on the proportions of dietary protein and starch that escape fermentation and are digested in the intestines.

 

The extent to which the protein in a supplement passes through the rumen intact is partly a function of its rate of degradation (solubility) in the rumen, and is likely to be influenced greatly by the rate of flow of fluid and small particles out of the rumen. The latter characteristic is influenced by processing of the feed (physical or chemical), the presence of green forage, the amount of protein reaching the duodenum and external factors such as temperature and exercise or work.

 

The same factors influence the supply of glucose and glucogenic precursors in terms of the amount of starch that is likely to bypass the rumen to the duo­denum. However, the nature of rumen fermentation will have a major influence in terms of supply of pro­pionic acid for glucose synthesis.

7.2   NUTRIENT SUPPLY vs PRODUCTIVE STATE

There is insufficient information to permit the pre­cise quantification of the proportions of the different nutrients required for different productive states (see Chapter 4). Nevertheless, the needs of animals can be approximated. The suggested scheme attaches rel­ative priorities to the groups of nutrients according to the physiological and biochemical processes undelying the expression of the particular productive state (see Table 7.2).

 

Table 7.2: Relative priorities attached to the require­ments for long chain fatty acids (LCFAs), amino acids (AA), oxidation (VFA) energy (C2) and gluco­genic energy (Synthesis energy C3:C6) according to the productive function of the animal

 

Relative priorities

 

C2

C3:C6

AA

LCFAs

Work

xx

xxx

x

xxxxx

Maintenance

xxxx

x

x

x

Late growth /

 

 

 

 

gestation

xxx x

xxx

xx

x

Early growth

xxxxx

xx

xxx

xx

High milk

xxxxx

xxx

xxxx

xxxxx

Medium milk

xxxxx

xx

xxx

xxxx

Low milk

xxxx

x

xx

xxx

Source: Preston and Leng 1984

 

The groups of nutrients to be varied for different productive states are:

Manipulation of the end-products of fermentation and digestion has been discussed in Chapter 5. In this section the relative needs for each class of nu­trients are related to the various productive states. Methods of achieving the optimum balance of nutri­ents are proposed, taking into account the constraints associated with the use of the feed resources that are likely to be available in developing countries.

 

VFA energy arises from fermentation in the rumen of all types of organic matter, though principally car­bohydrates. The principal way to increase VFA eergy in a particular feed is to increase the amount of it that is consumed and/or to increase its degrad­ability in the rumen by supplementing it with bypass protein or by treating the feed with alkali (mainly ammonia) or both.

 

Manipulation ofthe rumen to provide more protein and glucogenic precursors is still at the experimental stage. Dietary supplementation is the most obvious way of manipulating the supply of amino acids, glu­cose and glucose precursors that can be absorbed.

 

Most supplements are expensive and their use in ruminant nutrition competes with monogastric ani­mals and humans. However, if the primary feed re­source is a product which would have been wasted if it were not fed to ruminants, it can be argued that the ruminant uses the concentrate supplements more efficiently than monogastric animals (see Chap­ter 1). For this reason the term "catalytic" supplment has been used to describe supplements used in this way (Preston and Leng 1980). Milk, given in small amounts «2 litres daily) as a supplement to calves on a straw-or molasses-based diet, is a good example of a "catalytic" supplement.

 

It is essential that research should produce re­sponse relationships to distinguish economic from bi­ological optima. As a rule of thumb, the role of a supplement ceases to be "catalytic" when it com­prises more than about 30% of the diet dry matter. Beyond this point it assumes a major role and sub­stitution occurs.

 

The productive functions and the need for supple­mentary nutrients are discussed in order of the least to the most demanding.

7.2.2 Work

Work requires ATP generated from the oxidation of LCFAs, with obligatory requirements for glucogenic compounds and for amino acids (to repair the wear and tear of tissues and to replace protein secretions) (see Chapter 4).

The working animal can often obtain sufficient nu­trients from a nitrogen-deficient diet so long as it balances the protein-to-energy ratio needed for tissue turnover by "burning-off''' acetate that is in excess of requirements. However, bodyweight loss may restrict the period of work. If the work is to be prolonged and weight loss is to be minimised, the nutrients avail­able must be balanced so as to meet the needs of the working animal. The digestibility and the intake of the basal diet may also have to be increased by supplementing with urea to correct a deficiency of fermentable nitrogen in the rumen (see Chapter 4). This may be the only manipulation that is necessary, but supplements that are rich in fat and bypass pro­tein could be beneficial, particularly where the animal is in a productive state (eg. pregnant or lactating). If weight loss continues because work is prolonged it may be necessary to increase the degradability of the basal diet, ego by ammoniation (urea ensiling).

 

The mature, unproductive ruminant does not ap­pear to require nutrients over and above those pro­vided by efficient fermentative digestion.

 

Since the heavily working animal uses largely LCFAs and glucose (Pethick and Lindsay 1982a; Leng 1985), the supplements used should contain or pro­vide these substrates. This is particularly important in the case of LCFAs, since their absorption and use for fat deposition, and then mobilisation and use for work are much more efficient and require less glucose oxidation than synthesis of fat from acetate and its subsequent use in muscle metabolism.

 

7.2.3 Maintenance

Maintenance alone obviously requires less energy than work; thus the demand for amino acids relative to energy is proportionately higher than in the work­ing animal. This will always be provided by a rumen system that has sufficient fermentable N. Animals in negative energy balance for an extended period on low-N, roughage-based diets extract more digestible energy from the basal diet when it is supplemented with fermentable N (see Table 9.8).

7.2.4 Growth

Growing animals have a very high requirement for amino acids for tissue synthesis and for glucose for oxidation in specific tissues (eg. brain). In addition, glucose is needed as a precursor of macromolecules. The high demand for glucose in productive animals is discussed in Chapter 4 (see Figures 4.3 and 4.5).

 

It is imperative to recognise that high growth rates cannot be supported on the products of fermenta­tive digestion and that bypass-protein supplements are essential to take advantage of the VFA energy absorbed.

 

Many factors influence the level of protein supple­mentation to be used. Response relationships must be established that relate protein supply to animal productivity for each basal (carbohydrate) resource and for the available protein meals. The response pattern will vary according to the nature of the basal diet and the particular protein supplement. This is demonstrated by data taken from Bangladesh and Cuba. Cattle on ammoniated (urea-ensiled) rice straw, when supplemented with only 50 g of fish meal per day increased their liveweight gain three­fold (Figure 8.3). On a molasses-based diet, 450 g of fishmeal per day were needed to raise liveweight gain from 300 to 900 g/d (Figure 8.19).

 

In some countries, legumes appear to offer a low­cost solution to providing bypass protein on the farm. Based on the premise of using protein economically, the intake of these forages should be restricted and therefore it is preferable to grow the legume in mono­culture rather than as a pasture. The amount of by­pass protein in a legume (green or dry and used as a supplement) has not been estimated but is not likely to be high when it is used as a small proportion of a diet based on low-digesti bili ty roughage (see discus­sion of legumes as a supplement). It may be benefi­cial to grow tannin-rich legumes where these are to be used as supplements to crop residues, whereas, if they are to comprise a large proportion of the diet, low­tannin legumes may be more appropriate (eg. feeding Leucaena with molasses/urea) (Hulman et ai. 1978).

 

The tree legumes, ego Giiricidia, Erythrina and Leucaena, have great potential as sources of legume fodder because they are high yielding and perennial. They are also deep-rooted and may have access to water and nutrients unavailable to smaller plants.

 

In animals fed low-N diets supplemented with legumes there is still a need to ensure that ammonia concentrations in the rumen are adequate by supply­ing fermentable N, usually as urea. It is also im­portant that the protein source, which is usually in short supply, should be partitioned between as many animals as possible.

7.2.5 Reproduction

Increases in fertility brought about through nutri­tion are usually attributed to increased energy in­take. There is, however, evidence that the supply of glucogenic precursors relative to total energy is an important feature of the improved energy status.

Conception and puberty

Recent studies have demonstrated that even when animals are grazing apparently nutritious pasture, the "quality" of the energy can be a limiting fac­tor. At the same metabolisable energy intake (the basal diet was low-N Coastal Bermuda grass hay), animals reached puberty at lower liveweights when glucose availability in the animal was increased (Ta­ble 7.3); however, the availability of protein (from the diet that supplied the glucose) is unknown and similar responses could have been elicited by supple­mental bypass protein.

 

Table 7.3: Feeding monensin to growing heifers on a basal diet of Bermuda-grass hay and concentrates increased propionate and decreased butyrate propor­tions in the rumen VFAs. Puberty was accelerated as evidence by the greater proportion of heifers cycling by the end of the test period.

 

Control

Monensin

Liveweight (kg)

 

 

Initial

219

219

Final

313

319

Feed intake (kg)

8.0

7.7

Rumen VFA (% molar)

 

 

HAc

74

69

HPr

19

26

HBr

6

3

Total VFA (mM/litre)

65

67

Fertility (% heifers cycling)

58

92

Source: Moseley et al 1982

 

 

The effects of bypass protein on conception rates of cows grazing sub-tropical pasture during the dry season are shown in Table 7.4. A supplement provid­ing fermentable energy (molasses) had much less ef­fect on conception than a bypass-protein supplement, confirming the report of Moseley et al. (1982) that it is the "quality" of the energy (ie. energy in the form of glucogenic compounds) that is critical.

 

Table 7.4: Liveweight and conception rates of lac­tating beef cows (with first calf at foot) grazing na­tive pasture and supplemented with 1.86 kg of an energy concentrate (molasses 85%, cottonseed meal 12%, urea 17% and monammonium phosphate 1%) or 1.5 kg of a bypass protein meal (cottonseed meal) during periods when only dry pasture was available. There were 12 cows per group.

 

 

Liveweight

Pregnancy

Supplement

(kg)

(%)

 

Nil

302

10

 

Energy

332

20

 

Bypass protein

343

60

 

Source: Hennessy (1986).

 

 

The growth of the foetus

The growth of the conceptus has little effect on the protein and energy demand of ruminants until the last third of gestation, during which most of the foetal tissues are synthesised. Because of the low demand for nutrients by the pregnant uterus upto the begin­ning of the third trimester, it appears that nutrients provided by fermentative digestion can support the production of a calf or lamb with a normal birth weight. These animals are generally viable and will survive even where the diet of the dam is of low di­gestibility, provided that the diet is supplemented with urea. This was shown in studies in which urea was included in the drinking water of ewes on nitrogen-deficient pasture (Table 9.4).

 

Increases in calf birth weight were recorded when pregnant cattle given a basal diet of hay of low di­gestibility (45%) were supplemented with urea (Table 9.9). However, it was necessary to provide additional bypass protein to prevent body-weight loss or to pro­mote weight gain of the dam during pregnancy.

 

It appears that supplementing the diet with urea increases milk production to a level that ensures sur­vival of the offspring, but to allow the young animal to grow at a significant rate, milk yield must be in­creased further by feeding a bypass-protein meal.

Male fertility

Supplementary feeding has been shown to increase the fertility of male ruminants under extensive graz­ing conditions. In the extensive grazing systems in the dry tropics of Australia, mating of the beef herd usually starts immediately after the onset of the wet season. Elsewhere, bulls are often placed in the herd only 4 to 6 weeks into the wet season, even though the bulls may have lost 20% of their body weight dur­ing the dry season. Lindsay et al. (1982) showed that bulls could be maintained in good condition on low-N spear-grass pasture (which was also oflow digestibil­ity) by providing I kg of a protein supplement daily (Table 7.5). More importantly the circumference of the scrotum decreased considerably when no supplement was fed. There are strong indications that a bull with a smaller scrotal circumference is less fertile and has a lower libido (Blockey 1980). This shows that protein nutrition has an important influence on male fertility.

Table 7.5: The effects of supplementation with 1 kg per day of protected protein (80% formalde­hyde-treated cottonseed meal, 10% meat meal, 10% fish meal) on the liveweight change, feed intake and scrotal circumference of bulls fed spear grass pasture hay (Heteropogon contortus) containing 0.4% N.

Initial weight (kg)

433

433

Live weight change (kg)

- 40

+ 14

Feed intake (kg DM/d)

 

 

Roughage

5.55

7.74

Total

5.55

8.65

Change in scrotal

 

 

circumference (mm)

- 20

0.7

Source: Lindsay et al 1982

As with female fertility, there appears to be evi­dence for beneficial responses to manipulating pro­pionate production in the rumen. At the same feed in take, bulls reached puberty earlier and at puberty had a greater scrotal circumference and larger testi­cles when fed a diet giving high-propionate fermenta­tion than on a diet which resulted in low propionate concentration in the rumen (Table 7.6).

 

Table 7.6: Higher proportions of propionic acid in the rumen VFAs of growing bulls as a result of supple­mentation with the rumen manipulator "Lasalocid" are associated with greater testicular development and reduced both age and live weight at puberty.

 

Control

Lasalocid

Rumen VFA (% molar)

 

 

HAc

65

60

HPr

21

32

HBr

15

7

Total VFAs (mMjlitre)

87

83

Increase in scrotal

 

 

circumference (cm)1

3.1

5.3

Testicular volume (cm3)

57

91

Age at puberty (d)

471

437

Weight at puberty (kg)

379

366

Source: Neuendorff et al 1982

1.         From29 to 175 days

 

7.2.6 Milk production

The thesis developed throughout this book is that it is irrational to use large amounts of cereal grains for ruminant production in developing countries in the tropics.

 

This is in marked contrast with the strategies for milk production in industrialised countries where ce­real grains are the basis of the diet and these are eco­nomically priced in relation to the value of the milk; where nitrogenous fertilisers are readily available at competitive prices and the temperate climate allows ruminants to lose the heat produced by the digestion and metabolism of the large amounts of feed that are ingested by specialised dairy breeds (eg. Holstein-Friesian). The overall objective is to manage and feed specialised dairy cows to attain their genetic po­tential.

 

This has had the following consequences:

These technologies are not applicable to developing countries because the environmental conditions and the availability and prices of cereal grains are com­pletely different. Attempts to apply them in devel­oping countries have usually failed (Mason and Bu­vanendran 1982; Hodges 1984). Despite these expe­riences, such "technology transfer" continues to be advocated, and because grain-based concentrates are fed, milk is produced at the expense of the availabil­ity of human food. Where these highly nutritious feed resources could not be economically supplied, the re­sult has usually been disastrous because of low milk yields, impaired fertility and often high mortality.

 

The alternative to the establishment of a spe­cialised dairy industry is to encourage milk produc­tion from existing animal and feed resources, which are largely in the hands of small farmers. This means dependence on feeds such as crop residues, agro-in­dustrial byproducts and pastures of low digestibility and low N content. It also depends on the use of in­digenous cattle, which have often not been selected or developed for milk production, but rather for draught purposes or for survival characteristics.

 

The constraints to milk production using such re­sources are a function of the balance of nutrients re­quired for milk synthesis (see Chapter 4)). In sum­mary, it appears that a major constraint to milk pro­duction is the availability of glucogenic compounds to provide glucose for lactose synthesis, for oxidation and to provide the N ADPH needed for synthesis of milk fat.

 

There is good evidence that about 50% of the fatty acids of milk arise from dietary fat in large ruminants (Figure 4.16). This reduces considerably the imbaance between the needs for glucogenic energy reltive to total energy or protein in milk and that in the products of rumen digestion. The ewe appears to be disadvantaged in this respect (see Table 4.8). The higher the availability of alimentary LCFAs, the better the ruminant is able to cope with milk produc­tion (see Chapter 4). However, a minimum fat level in the diet is required in order to spare glucose for other purposes such as milk lactose synthesis.

 

For many feeding systems in the tropics the level of fat in the diet could be a primary constraint to milk production, particularly with diets based on molasses or sugar-cane.

 

The ruminant species that produce high-fat, 10w­protein milk (eg. buffaloes, sheep and camels) are likely to be the most suitable for producing milk on low-protein crop residues and sugar-rich agro­industrial byproducts, provided that fat is available from the diet.

 

Supplementation of lactating animals, particularly those on diets based on crop residues, sugar-rich agro­industrial byproducts and tropical pastures, should aim to correct the imbalances of nutrients for milk production. Supplementing the diet with bypass pro­tein usually increases feed intake and, as a conse­quence, increases milk production. But to balance energy quality, fat must be mobilised and glucose diverted from oxidation and tissue synthesis to lac­tose production; in these circumstances animals tend to lose body weight (0rskov et al. ] 977). Adding dietary fat may reduce this effect (see Chapter 4). Adding a source of bypass starch in such a diet bal­ances the ratio of glucogenic precursors to protein and energy and will tend to prevent mobilisation of body fat. Bypass starch does not stimulate feed intake and milk production is affected only slightly (Table 4.14).

 

The points to be stressed are that:

7.2.7 Wool or hair production

The effect of nutrition on wool production appears to be dependent almost entirely on the quantity and relative proportions of amino acids absorbed. There­fore, feed intake is the primary limitation to wool or fibre growth although at anyone feed intake, wool growth can be increased by altering the balance of protein relative to energy in the products of fermen­tati ve digestion (eg. by removing protozoa from the rumen (see Chapter 4). Thus on diets that require fermentative digestion, including those based on sug­ars or fibre, a bypass-protein supplement will increase wool growth (Table 7.7).

 

 Table 7.7: Goats and sheep on "high quality" carbohydrate feeds do not produce without bypass-protein supplements. Bypass starch appeared to also increase productivity. The animals were given a basal diet which was readily fermented in the rumen (35% oaten chaff, 25% maize flour, 15% molasses, 15% sucrose, 5% barley grain, 4.5% urea and 0.5% complete mineral/vitamin mixture). The basal diet was supplemented with 5% protected casein (formaldehyde-treated) 01' 5% protected casein and 10% cracked rice (bypass protein and starch).

 

Basal

Bypass protein

Bypass protein + starch

 

Goats

Sheep

Goats

Sheep

Goats

Sheep

Daily gain (g/d)

32

45

68

107

81

119

Patch weight*

0.54

0.74

0.82

1.27

0.76

1.11

Feed intake (g/d)

465

538

604

755

664

736

Feed conversion (g DM/g gain)

14.8

11.9

8.9

7.0

8.2

6.2

Rumen fluid t1/2 (hr)

16.1

14.1

8.6

9.0

12.1

12.7

Source: Throckmorton et al. (1982).
*
Wool or hair clipped from a 10 cm2 mid-side patch (
mg/cm2)d.  

 

 

7.2.8 Carry-over effects of ibalanced nutrition in early life

Under pastoral conditions with alternating wet and dry seasons, young stock post-weaning are almost ivariably S1l bjecied to a deficiency of protein relative to energy in the nutrients absorbed from the diges­tive tract and the balance of nutrients is aggravated by the low fat content of dry pastures. This results in reduced feed intake and energy deficiency.

 

In societies that depend on milk as a dietary staple, the young calf and people compete for milk. This is indicated by the purchase of maize by Kenyan pas­toralists during periods of low rainfall (and therefore at a time when pastures are deficient in protein and fermentable N). The maize purchases by the family were inversely related with milk off-take (Figure 7.1). Reducing the amount of milk available for the calves can be highly detrimental, particularly when the herd is grazing dry pastures or is being fed on crop residues. The cows will yield less at this time due to the imbalance of nutrients in the feed available. Thus the calf suffers on two counts: an imbalanced basal diet and a reduction in the supply of bypass nutrients from milk.

Figure 7.1: The influence of rainfall (active grass growth) on milk offtake and maize purchases (maize) in OlkarkaT ranch in Kenya. during periods of high milk production, maize purchases by the family are reduced, indicating substitution of cereal by milk in the family's diet. This shows the competition between human needs and those of the calves for available milk supplies (Source: ILCA 1985)

 

The male stock, because they are less valuable and not generally given supplements, often die from inani­tion resulting from protein deficiency. This is mani­fested as a low intake of the available feed, usually straw or grass which is low in fermentable Nand lacks the bypass nutrients that the calf would oterwise have received from the milk, but which is used instead by the family. In countries such as India, fe­male offspring are more prized and are often given supplements of young grass and sometimes byprod­ucts such as cottonseed meal. Their survival rate is much higher than that of the males.

 

Male stock that survive are often reared as replace­ment oxen, and their ultimate body size is important since, in countries where feed resources are scarce, a single ox for work is an obvious advantage in conserv­ing valuable feed resources. However, as body size is related to work capacity, a large animal is needed if the move to a single ox is to be successful.

 

In some countries there have been suggestions that the mature size of cat tIe and buffalo in the na­tional herd is being lowered because large animals are slaughtered instead of being used as sires. This has often led to special breeding programmes being es­tablished to increase the size of animals. As has been emphasised in Chapter 2, "breeding without feeding" can be highly irrational.

 

There are indications that cattle can be perma­nen tly stun ted if they are fed imbalanced diets in the pre-and post-weaning periods. The stunting may be due to reduced feed intake, particularly during dry seasons when the level of both fermentable Nand bypass protein limits intake and efficient utilisation of the available feeds (pasture and straw). It may also be due int.er alia to protein deficiency. Two sets of information support this thesis.

Table 7.8: Comparisons between productivity indices for cattle in traditional grazing systems and on ranches in four African countries. The differences between the two groups in all countries is taken as supporting evidence for protein under-nutrition in cattle in traditional grazing system. The evidence for protein supple­mentation affecting birth weight, weaning weight and mature body size is given in Chapter 9

 

 

 

 

Live weight (kg)

 

Country

Breed

System

Birth

Weaning

2 years

4 years

Mali

Sudanese Fulani

traditional

17

55

125

200

 

 

ranching

21

79

220

280

Nigeria

White Fulani

tradi tional

20

55

140

240

 

 

ranching

24

96

245

350

Ethiopia

Boran

tradi tional

20

55

150

260

 

 

ranching

25

180

265

420

Botswana

Twana

traditional

26

]20

260

300

 

 

ranching

31

]80

360

400

Source: ILCA 1985 (Unpublished)