The value of protein content of sorghum grain in pig diets

Abstract

In three experiments, a total of 112 pigs were individually fed sorghum grain-soybean meal diets based on either high protein grain (10.9 to 13.3 per cent crude protein, air dry basis) or low protein grain (6.5 to 7.4 per cent crude protein, air dry basis). Soybean meal was incorporated in the diets at four levels-16.6, 13.8, 10.7, and 7.4 per cent. In experiment 1 the experimental diets were fed from weaning to 86 kg liveweight. In experiment 2 the experimental diets were supplied from weaning to 45 kg liveweight with a common standard diet being provided from 45 kg liveweight to slaughter, In experiment 3 a common standard diet was supplied from weaning to 45 kg liveweight. The experimental diets were commenced at this liveweight and continued until slaughter. Level of protein in the grain had no significant effect on growth rate or feed efficiency in any experiment, but in experiment 2 the mean eye muscle index of the pigs receiving the high protein sorghum diets was significantly greater than that of the pigs receiving the low protein sorghum diets. As level of soybean meal in the diet decreased, there was a general tendency for growth rate and feed efficiency to decrease. In experiment 1, growth rate and feed efficiency were lower in pigs receiving the 10.7 and 7.4 per cent soybean meal diets, but only prior to a liveweight of 45 kg. In experiment 2, each reduction in level of soybean meal resulted in a reduction in growth rate and feed efficiency prior to 45 kg liveweight. There was no difference between groups from 45 kg to slaughter, when all pigs received the same ration. In experiment 3, which commenced at 45 kg liveweight, growth rate and feed efficiency were reduced only when the level of soybean meal was lowered to 7.4 per cent.