Mineral and vitamin supplementation of diets for growing pigs. 1. Wheat-based diets and the effect of preventing cross-coprophagy on the response to supplementation

Two factorial experiments examined the effects of mineral and or vitamin supplementation on the performance of 64 growing pigs. The wheat-based diets contained either meat-and-bone meal (with some fish meal up to 32 kg liveweight) or solvent-extracted soybean meal (SBM). A basal supplement of vitamins A and D2 was added to all diets. The pigs were individually fed at restricted intakes between 18 and 73 kg liveweight and housed as mixed treatment groups. In a third factorial experiment, 32 growing pigs were restrictively fed a wheat/SBM diet from 20 kg liveweight to 75 kg or for 20 weeks. The pigs were individually housed to prevent cross-transfer of vitamins from supplemented to unsupplemented pigs by way of the faeces (cross-coprophagy). Mineral supplementation of the wheat/animal protein diet (experiment 1) did not affect pig performance, but improved the growth rate and feed conversion ratio of pigs fed the SBM diet (experiment 2) by 45 and 32 per cent respectively. Omitting the mineral supplement from the SBM diet caused loss of appetite, soft bones, joint and foot abnormalities and lameness in many pigs; 5 out of 16 pigs did not reach slaughter weight. Gilts fed the SBM diet were less tolerant of mineral deficiencies than barrows. They also stored less calcium in their bones when minerals were added to the diet. There was no response to vitamin supplementation even though both diets, but especially the SBM diet, were apparently deficient in a number of vitamins. The SBM diet provided 76, 83 and 53 per cent respectively of the pigs' estimated requirements for riboflavin, pantothenic acid and vitamin B12. In experiment 3 the SBM diet supplied 64, 80 and 28 per cent of the pigs' riboflavin, pantothenic acid and vitamin B12 requirements. As in experiment 2, there was no response to vitamin supplementation. Cross-coprophagy was thus most unlikely to have caused the lack of response to vitamin supplementation in the group-housed pigs of experiment 2. Mineral supplementation improved growth rate by 108 per cent and feed conversion ratio by 40 per cent.