Amino acids soya bean protein

Soya beans contain oil (180-220 g kg ) and approximately 35-45% protein (370-420 g kg ). The amino acid content differs significantly from that of wool and silk protein (see Table 13.1). Soya bean protein content is higher than that of peanuts (approximately 25% protein) and maize (approximately 10% protein). The principal components of this protein are... 

Table 13.1 Percentage of amino acid content in soya bean protein compared with that of wool and silk...

Birds eat sufficient food to satisfy their energy intake, but this does not mean that they will eat enough protein, unless the protein proportion in the rotation is high. Protein quality is also important, the two most essential amino acids being lysine and methionine. The best quality protein for all poultry is white fishmeal (banned only for ruminants by the Soil Association). The best vegetable protein is soya bean which is low in methionine, but this can be made up by using sunflower meal in the ration. 

The nitrogen sources may be ammonium salts such as citrate, tartrate, malate, succinate, oxalate, acetate and the like amino acids and their mixtures, peptides or proteins, their hydrolysates, meat extracts, hydrosoluble fractions of cereal-like com or wheat corn malt extract, corn steep liquor, soya-bean meal, peanut meal, chick-pea meal, cotton bean meal. 

In some circumstances it is possible to express protein requirements in terms of total protein alone, for example if animals are fed on a limited range of foods of known amino acid composition. This is the case for growing pigs in the USA that are fed mainly on maize and soya bean meal. Such a simplified approach cannot be sustained when a wider range of foods and by-products are used, and when diets must be formulated not only to maximise growth but also to optimise carcass composition. Feed compoimders therefore formulate pig diets to meet the requirements for at least three amino acids (lysine, methionine -I- cystine and threonine).They will also take into accoimt the availability of certain amino acids, assessed from digestibility at the terminal Ueiun (as explained in Chapter 10). 

Meeting the requirements of non-ruminants for a balanced supply of essential amino acids requires the use of expensive protein sources, such as fishmeal, or high levels of less well-balanced protein sources such as soya bean meal (see Chapter 13). Economics dictate that the latter option is usually taken, and, in order to meet the requirements for the limiting amino acid, an excess of total protein has to be supplied. This is deaminated and the nitrogen is excreted both processes require energy, and such protein oversupply is wasteful in terms of both protein and energy metabolism. In addition, the excreted nitrogen may be a source of pollution in the environment. 

Pig and poultry diets based on cereals and vegetable protein sources are now routinely supplemented with L-lysine hydrochloride (supplying 780 g lysine/kg), dl-methionine and L-threonine. A diet for a finishing pig, which has to contain 10 g lysine/kg, required a combination of 750 g barley and 250 g soya bean meal/kg, and this mix has a crude protein content of 185 g/kg (see Appendix 2, Table A.2.2.2). With the inclusion of 2 g of lysine hydrochloride, the same lysine content can be achieved with a mix of 808 g barley and 190 g soya bean meal, and the protein content is reduced to 165 g/kg. Such reductions in crude protein content have maintained a balanced supply of amino acids and resulted in improved rates of liveweight gain and food conversion efficiency. It is important that the supplementary acids are not used excessively to satisfy the animal s requirements, since this may bring about an undersupply of other essential amino acids. 

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