The effect of dietary energy level and protein: energy ratio on nitrogen and energy balance, performance and carcass composition of pigs weaned at 3 weeks of age

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Abstract
Four diets were formulated from cereals, animal and vegetable protein supplements and tallow, to contain digestible energy (DE) concentrations of 14·1 or 17·1 MJ/kg and crude protein concentrations of 12·7 or 17·0 g/MJ DE in a 2 X 2 factorial design. In each of two experiments, pigs were weaned and allocated to dietary treatments when 21 days old and were fed twice daily to appetite. In experiment 1, six replicates of four male littermates were used. They were individually fed in metabolism cages and continuous energy and nitrogen (N) balances were made from 28 to 63 days of age. In experiment 2, three male and three female pigs were slaughtered at weaning to determine initial body composition, and three replicates of four littermates of each sex were allocated to the dietary treatments. The latter were fed in treatment groups in flat-deck pens and slaughtered at 63 days of age.In experiment 1, increased energy concentration reduced food intake only slightly and improved liveweight gain and food: gain ratio; higher protein concentration increased gains only at lower energy concentration. Daily N balance improved with increased energy and protein concentration but the response to protein was greater with the low energy diet. Dietary energy was efficiently utilized even with 163 g tallow per kg diet. From 63 days of age until slaughter at 60 kg all pigs were given the same grower diet to appetite. Performance was not affected by previous treatments.In experiment 2, food intakes were higher than in experiment 1 and tended to be reduced to a greater extent with the higher energy concentration; live-weight gains were similar for all treatments and food: gain ratio tended to improve in response to higher energy and protein concentrations. Dietary energy level had no effect on carcass fat content but the higher protein level reduced fat deposition. N retention tended to be lower for the low energy, low protein diet compared with the other three diets. Dietary effects on the amino-acid composition of the carcass were small. Carcass amino-acid ratios at 3 and 9 weeks were similar to published values and there was a tendency for higher amino-acid concentrations (g/16 g N) at 9 weeks than at 3 weeks.