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3. Feed values and feeding potential of major agro-byproducts


3.1 Feed values
3.2 Feeding potential of major byproducts


3.1 Feed values


Molasses
Groundnut cake
Cottonseed cake
Sunflower seed cake
Palm kernel cake
Fishmeal


Trends in production, consumption, and trade of major agro-byproducts in Sub-Saharan Africa (SSA) have been discussed with a view to establishing their potential availability for animal feeding. In this section, particular attention is focused on the feed values of these byproducts and their feeding potential for cattle.

Molasses and oilcakes in SSA were and are being fed almost exclusively to cattle. Molasses is mostly used as an energy supplement or as a carrier for urea in utilizing non-protein nitrogen (NPN) whereas oilcakes are incorporated into diets as protein supplements. Because of their high protein content, oilcakes could also be used to upgrade low-quality roughage to a maintenance diet. Table 2 provides the nutritional characteristics of the major byproducts in Sub-Saharan Africa. Since variations in feed values of these byproducts are to be expected between byproduct samples and seasons, the nutrient values presented in this table should be taken as averages of information available. Where information on the nutritive value of the byproduct is not available within the Subcontinent, nutrient values from international tables have been taken as proxies.

Molasses

Molasses can be used for all classes of livestock. However, the use of molasses in rations for cattle feeding is more extensive than with any other livestock species. As an energy supplement, molasses can be used as a substitute for grain. As such, molasses has often been used to supplement cattle grazing poor-quality roughages when energy intake is a limiting factor. However, molasses is a poor source of protein (table 2) and needs to be supplemented with urea as a non-protein source of nitrogen for sustaining higher levels of production. The constraint in utilizing high levels of molasses is its toxicity. Experience indicates that molasses may be toxic when fed in large quantities. As a result, recommended inclusion rates do not usually exceed 15% for cattle and 8% for sheep (Gohl, 1981).

Table 2. Feed values of major agro-by products in Sub-Saharan Africa (Data expressed on an As-Fed and Dry Matter Basis for cattle)

Byproduct

Production ('000MT, 1984)

Dry Matter (%)

ME (Meal/kg) (%)

CP (%)

DP (%)

TDN (%)

Molassesa

1255

AF 75

2.47

3.2

1.8

68

DM 100

3.29

4.3

2.4

91

Groundnut cakeb

442

AF 94

3.27

46.4

41.7d

83

DM 100

3.50

49.6

44.6d

89

Cottonseed cakeb

497

AF 92

2.63

36.5

23.1d

68

DM 100

2.87

39.8

25.1d

74

Sunflower seed cakec

63

AF 93

2.49

41.5

36.9

69

DM 100

2.68

44.6

39.6d

74

Palm kernel cakee

271

AF 92

3.05

18.8

15.9

84

DM 100

3.31

20.4

17.3

91

Fish mealb

29

AF 92

3.38

60.9

54.2

85

DM 100

3.69

66.2

59.2

95

Sources:
a - Crampton and Harris, 1969
b - Kearl, 1982
c - NRC, 1984
d - Calculated by (DPa/CPa) * CPb from 5 - 04-738 in Crampton and Harris, 1969
e - Gohl, 1981. The values are for sheep, but are taken as proxies for cattle

Note:
ME = metabolizable energy; CP = crude protein
DP = digestible protein;
TDN = total digestible nutrients.
AF = As fed
DM = Dry matter

Groundnut cake

Groundnut cake is generally a safe feed for all classes of livestock. Unlike molasses, the use of groundnut cake has no general limitations in livestock feeding. Groundnut cake has been used as a protein supplement in cattle feeding. However, its low fiber and high protein contents (table 2) make it an even more valuable ingredient for poultry rations. Thus most groundnut cake consumed internally in Sub-Saharan Africa during the 1970s and the 1980s may have gone to poultry because of rapid poultry development during the period. The main constraint to its utilization is its easy contamination by toxic substances due to bad storage. The most dangerous substance is aflatoxin.

Cottonseed cake

Cottonseed cake is an excellent protein supplement for ruminants, but its use in monogastric rations is restricted due to the presence of gossypol. In normal concentrations, gossypol has no toxic effect on cattle, but it has been shown that liveweight gain in beef cattle is reduced when the gossypol content is high. When cottonseed cake is used in poultry and pig rations, levels of up to 10% are usually recommended (Chicco and Shultz, 1977). In Sub-Saharan Africa, cottonseed cake has been used extensively in ruminant feeding.

Sunflower seed cake

While sunflower seed cake has been used extensively in ruminant feeding in temperate countries, it has not received much attention in the literature in Sub-Saharan Africa, Like groundnut cake, sunflower seed cake is also a source of high-quality protein (table 2) and can be used freely in balanced diets for poultry and pigs owing to the absence of toxic compounds. Sunflower seed cake, produced in Sub-Saharan Africa, was almost entirely consumed as feed between 1973 and 1984. Although no information on aggregate feed use of this byproduct by species of livestock is available, much of it has probably been fed to monogastric animals rather than to ruminants.

Palm kernel cake

In spite of its comparatively high oil content, palm kernel is usually dry and unpalatable and is not readily accepted by all classes of livestock. There seems to be no nutritional limitations to its use in ruminant feeding when it is mixed with well-liked feeds. Palm kernel cake is relatively low in protein content as compared to the other oilseed cakes in Sub-Saharan Africa (table 2). Although, some observations (Chicco and Shultz, 1977) indicate that palm kernel cake can be used in rations for monogastrics, it has been largely used in Sub-Saharan Africa for cattle feeding, especially dairy animals where it can serve as the main protein source (Adegbola, 1977).

Fishmeal

Fishmeal is among the best sources of high-quality protein for animals (table 2). In Sub-Saharan Africa, most of the fishmeal fed has probably been used in poultry and pig rations. Much of Sub-Saharan fishmeal production between 1961 and 1984 was exported. However, in some regions, e.g. East and Southern Africa domestic feed use was in excess of domestic production and the gap was presumably filled with imports. Use of fishmeal in ruminant feeding is rare due to its high cost although many experiments with cattle indicate better responses to fishmeal than to other sources of protein (creek et al, 1974; Preston and Willis, 1974).

3.2 Feeding potential of major byproducts

Protein is an essential nutrient for animals, and more importantly for dairy cows because milk production requires more protein than meat production. This is because when inadequate amount of protein are fed milk production can not be sustained due to the negative effect on the animal's utilization of body fat (Orskov and Dolberg, 1985). Therefore, if good milk yields are to be achieved, protein requirements of dairy cows must be met. For this reason, an attempt is made in this section to estimate the feeding potential, for protein supplementation of milking cows, of the available oilseed cakes in Sub-Saharan Africa.

In this estimation, annual feed requirements of milking cows made by Crampton and Harris (1969) were used. They assumed that a milking cow, producing 1800 kg of milk annually, needs about 450 kg annually of concentrates (including both energy and protein feeds). Further, based on available dairy feeding practices in Sub-Saharan Africa (Murder et al, 1973), it is assumed that the concentrate ration should contain at least 14 percent of crude protein. Using the above information and assuming that cereals3 will provide the energy in the diet of concentrates, very crude approximations were made to gain a relative idea on the number of animals these byproducts would supplement. The crudest part of the exercise is the implicit assumption that cereals are in relatively plentiful supply.

3. It is assumed that cereal grains contain at least 8 percent crude protein.

The results4 in table 3 indicate that groundnut cake could have supplemented approximately 6.1 million head of milking cows in 1984 while cottonseed cake would supplement about 5.2 million heads. On the other hand, sunflower seed and palm kernel cakes would supplement about 0.8 and 1.1 million head of dairy cows respectively. This evaluation is made on the assumption that no byproducts would have been exported in 1984 and that they were readily available for supplementing dairy cows. It should be noted that this evaluation omits fishmeal because fishmeal is mostly fed to poultry.

4. The resules in table 3 are derived through the following procedure. The percentage of the protein-rich oilseed cake in the diet of 450 Kg of concentrate per cow is calculated as follows:

p(CP) + (1-p) * (.08) = 14

Where p = percentage of oilseed cake in the diet of concentrates, 1-p = percentage of cereals in this diet, and CP = crude protein content (proportion) of the byproduct. This formula, of course, overlooks the contribution of other feed sources than the 450 Kg of concentrates such as roughages. But, nevertheless it can provide a good approximation since protein content from roughages is generally low. This percentage is then applied to the annual feed requirement to determine the requirement per animal and per year for oilseed cake. Total byproduct available is then divided by oilseed cake requirement per animal to obtain the approximated number of milking cows the byproduct can supplement every year.

Table 3: Feeding potential of major agro-byproducts in Sub-Saharan Africa in 1984.

Byproduct

Production (' 000 MT)

Requirement/animal/year (Kg)

Dairy herd potentially supportable ('000 head)

Groundnut cake

442

72

6139

Cottonseed cake

497

95

5232

Sunflower s. cake

63

81

778

Palm kernel cake

271

243

1115

Molasses

1255

400

3138

The above calculations were based on the assumption that cereals would provide the energy in the diet of concentrates. However, if cereals were to be replaced by molasses, a cow, producing 1800 kg of milk per lactation, would require about 400 kg of molasses per year. This implies that the quantity of molasses available in 1984 would supplement about 3.1 million head of milking cows (table 3).


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