AMINO-ACID SUPPLEMENTATION OF CEREAL-BASED DIETS FOR NONRUMINANTS

Cereals are deficient in several essential amino acids including lysine, threonine and tryptophan. In addition, recent studies with pigs and poultry indicate that lysine, threonine and tryptophan are also the least digestible of all the essential amino acids in cereals. Under practical conditions, these limitations may be rectified by the judicious use of suitable protein-rich ingredients and pure amino acid supplements. However, for several heat-processed protein concentrates, lysine and threonine may be absorbed in forms that are inefficiently utilised by the pig for optimum growth and feed efficiency. Other evidence suggests that methionine, lysine and tryptophan may be utilised more efficiently by the broiler chick when provided in pure form rather than as components of intact protein, particularly with cereal-based diets containing relatively high concentrations of groundnut meal or maize gluten meal. Supplements of pure lysine and threonine are effective in enhancing the amino acid profile of barley-based diets to the ideal balance for growing pigs, but frequency of feeding may determine efficiency of utilisation. Although reductions of protein levels in pig diets through the extended use of crystalline amino acids should be pursued to improve efficiency of protein utilisation and to reduce environmental pollution, deleterious imbalances may occur with adverse effects on pig performance. Evidence is presented to show that amino acid imbalances precipitate ill-effects by reducing food intake, but the efficiency of utilisation of the first-limiting amino acid remains unaffected.