Effects of dietary fat, age and sex of broilers on their requirements for essential and non-essential amino acids

Abstract

An experiment was conducted to study the variation between sexes of broilers in the requirements for essential (EAA) and non-essential (non-EAA) amino acids and the effect of tallow on these requirements. The practical diets contained a balanced proportion of ten EAA which were expressed collectively as per cent of diet. The difference between dietary percentages of protein and EAA was expressed as per cent non-EAA. In the first three weeks, both sexes performed optimally with 7.6 per cent EAA, 11.5 per cent non-EAA and 11.3 MJ kg-1 energy. However, female chicks responded more to the increase in non-EAA than to EAA (significant interaction P < 0.05). Between three and five weeks of age, maximum growth and best utilization of feed were obtained with diets containing 6.8 and 6.1 per cent EAA, 10.5 per cent non-EAA and 13.4 and 11.3 MJ kg-1 energy for males and females respectively. Beyond five weeks of age, both sexes required 5.8 per cent EAA, but males appeared to require higher levels of non-EAA than females. Both sexes utilized the feed more efficiently when fed higher energy diets (13.4 MJ kg-1). Addition of tallow to diets adequate in amino acids without excess, depressed growth rate of both sexes with the males being more affected than females. The growth depression was absent on diets having higher levels of amino acids. It is postulated that tallow may contain a factor that reduces the availability of amino acids. The study has shown the potential benefits to the broiler industry that could result if diets for each sex of birds of particular ages were formulated on the basis of amino acid content and composition rather than crude protein. The study has also demonstrated that tallow may depress growth unless additional amino acids are also supplied. Avenues for further work are discussed.