Oil seed meals as source of limiting amino acids
Generally ruminants are not perceived to have a requirement for essential amino acids as the rumen microbes can synthesis essential amino acids from non essential amino acids provided the other conditions are met. However, in high yielding dairy animals, proteins which reach the small intestine are often deficient in methionine, which is therefore considered to be the first limiting amino acid. The other limiting amino acids could be either one or more of the following acids such as lysine, phenylalanine, histidine and threonine. Oil meals hence play a major role in providing these limiting acids under specific circumstances. A good example is that most of the cereal grains are severally deficient in lysine, while this particular amino acid is relatively present in higher levels in soybean meal. Researchers have concentrated their concerted efforts on manipulating the quantities of such amino acids delivered post-ruminally for digestion, absorption and subsequent supply to the mammary gland.
In order to reduce the cost of feeding animal nutritionists have succeeded in replacing the high quality oil meals such as soybean meal being prohibitive in cost with other medium / low quality oil meals in the current day rations of milch cattle. It is now possible to replace 50 % of groundnut cake protein with deoiled sunflower cake without affecting the milk yield, FCM yield, fat, total solids and SNF percentages in the milk.
Inclusion Rates in Livestock Rations
It is important to assess the feed value of by-products in relation to the type of animal and the system of production in which the material is used. Thus low quality by-products are best suited to use with animals which have already low nutrient requirements such as dry dairy cows. Such feeds may also be used tactically at times of feed shortage to reduce the cost of the diet. By-products of relatively better quality are most appropriately used in more intensive systems such as pig and poultry production. They also have wide application in ruminant livestock operations. Thus oilseed cakes and animal by-products regularly form part of compounded feeds meant for high yielding dairy cows . The fact that many are heat-treated means that the protein is less readily degraded in the rumen and more likely to enhance the total supply of amino acids to the animal.
There are clear limitations to the extent to which certain by-products may be recycled directly into the complete feeds of livestock. Apart from a low feed value, there may also be logistical problems of matching their availability to the supply of animals for their consumption. This problem may be exacerbated by a short life of the by-product and restrictions on use imposed by compositional factors such as toxins or physical factors, which might be associated with rapid deterioration. Strategic supplementation is justified because of regular feed shortages that occur and the fact that ruminants subsist for most of their life on agro-industrial by-products on small farms. Added costs of detoxification and supplements often discourage by-products use at higher level. There is a need for future systematic research on the optimization of the use of agro-industrial by-products in complete feeds and in developing strategies for their optimum supplementation in different livestock species.