NUTRIENT REQUIREMENTS FOR CANADIAN YORKSHIRE SWINE: III. A STUDY OF THE U.S. N.R.C (1959) NUTRIENT STANDARDS FOR SWINE BY LINEAR PROGRAMMING

Pigs were individually fed rations electronically formulated by linear programming methods, with 14 nutrients under experimental control in least-cost rations. The test periods involved three successive phases between weights of 50–200 pounds with ration changes at 100 and 150 pounds. The criteria included weight gains, feed consumption, digestibility or energy and protein, and carcass measurements at 200 pounds.Five grower rations were fed to the pigs between 50–100 pound weights: 1) a control: 2) a ration with nutrient specifications equal to the minimum requirements; 3) as 2), plus 25 p.p.m. aureomycin; 4) a ration having levels of 12 nutrients increased by 15 per cent over the minimum requirements; 5) as 4) plus 25 p.p.m. aureomycin.Four finisher rations were tested, involving the four possible combinations of digestible energy (DE) and protein levels as specified for ’meat’ and ’bacon’ type pigs at 100- and 150-pound weights.The results obtained in the growing period indicated significant superiority of rations with augmented nutrient levels. By comparing the nutrient contents of the various rations it was concluded that rations based on minimum requirements were adequate in methionine, riboflavin, pantothenic acid, calcium and vitamin B12. On indirect evidence it was considered improbable that vitamins A and D, zinc or phosphorus NRC specifications were too low. The failure of the ’minimum standards’ ration appeared to involve protein, lysine and/or tryptophan levels. All pigs, however, utilized their DE more efficiently than NRC standards imply. The question of an optimum DCP:DE ratio is discussed. The antibiotic had no significant effect on gains or feed efficiency but, even though discontinued at 100-pound weight, aureomycin influenced carcass quality.The finishing period results favored higher protein levels and lower DE levels from the standpoint of carcass quality but gains equal to NRC standards were possible with less DE and, in the 150–200 pound weight range, with lower DCP:DE ratios than specified for bacon pigs.