The present investigation is the sequel to an earlier pig-feeding trial in which a diet supplying only half the standard amounts of protein supplement, in the form of a mixture of feeding blood meal, dried separated milk and ex. soya bean meal, was found to give as good results from the standpoints of rate of growth, efficiency of food conversion and carcass leanness and quality, as a diet that contained the full standard allowances.

It was considered desirable to repeat this initial exploratory experiment, making use this time of a totally different form of protein supplement, since the question of the biological efficiency of the protein supply might conceivably be of critical importance at the lower levels of protein feeding. In the present trial, therefore, the mixture of the three protein foods was replaced by a single protein food, namely, white fish meal. The standard-protein treatment C supplied 12% of white fish meal up to 90 lb. live-weight, 10% from 90 to 150 lb., whilst from 150 lb. to slaughter at about 200 lb. live-weight, the white fish meal was omitted from the diet, its place being taken by 5% of ex. soya bean meal. The corresponding allowances of protein food in the low-protein treatment B were 5, 4 and 3% respectively. The low-protein treatment A, which was introduced as a link between the previous and the present trials, contained the protein supplement composed of feeding blood meal, dried separated milk and ex. soya bean meal and supplied the same amount of digestible protein as was contained in the low-protein treatment B.