The importance of protein quality in animal feeding

The importance of protein quality for practical rations becomes evident as soon as an attempt is made to economize and to establish for such rations the lowest level of protein that will give efficient production. Woodman & Evans (195 I) demonstrated this point with pigs fed on a simplified barley-fine-bran ration. Supplementation with fish meal at the rate of 4.2% protein gave efficient production that could be attained with groundnut meal only when included at the rate of 9*90/0 protein. In laying experiments, the difference between fish meal and groundnut meal was reflected in egg production only when the total protein content of the ration was reduced to r I % (Carpenter, Duckworth & Ellinger, 1954~~). The same proportions of fish meal and groundnut meal in a 14% crude-protein ration gave equal egg production. Consequently, economies that are permissible with a high-quality protein may not be so with a concentrate of a poorer quality. The principal aim of animal production is the economic and efficient conversion of feeding-stuffs. Financially, the real economies depend mainly on market conditions. Economy in terms of protein-also important to us as importers of a large proportion of concentrates-can be achieved by the correct allocation of available feeding-stuffs and by the conservation of quality during their production. The formulation of economic rations depends on knowledge, on the one hand, of the function of the rations in terms of the animals' requirements and, on the other hand, of the way to use available feeding-stuffs to fulfil these requirements. The poorerquality concentrates may then be included in successful rations, provided their limitations are recognized and corrected. Here, the feeding of non-ruminants will be considered and that only under intensive systems of management where requirements must be satisfied entirely by the rations. The utilization of protein by ruminants is, to a large extent, governed by the metabolism of the rumen micro-organisms. Criteria that determine protein quality under those conditions have been discussed by Chalmers & Synge (1954). Should the early weaning of calves become an established practice, many considerations given here may find application in calf rations used during the period before rumen activity becomes fully developed. Practical rations are generally compounded to contain protein at levels higher than the requirement determined under experimental conditions. This excess is regarded as a margin of safety which compensates for fluctuations in the quantity and