Mineral and vitamin supplementation of diets for growing pigs. 3. Salt, calcium and phosphorus, and trace mineral supplements in a wheat/soybean meal diet

Abstract

A 2 x 2 x 3 x 3 factorial experiment with 72 growing pigs examined the effect of adding salt, calcium and phosphorus (Ca + P) and trace minerals (TM-manganese, zinc, iron and copper) to a wheat/soybean meal diet. Gilts and barrows were individually fed at restricted intakes from 20 kg liveweight. Pigs required both salt and Ca + P to reach slaughter at 73 kg. Without these minerals they stopped growing; lameness and broken bones were also common. All pigs fed salt plus the higher level of Ca + P (0.84 and 0.57 per cent, respectively) completed the experiment but only half those fed salt plus the lower level (0.42 and 0.29 per cent Ca + P, respectively) did so. There was a response to salt within three weeks. In the first four weeks, 0.125 per cent added salt improved growth by 26.5 per cent and feed conversion ratio by 21 per cent. The results indicated that growing pigs require less sodium than currently estimated (Agricultural Research Council). A response to both levels of supplementary Ca + P was seen after about seven weeks with salt and nine weeks without salt. In the first eight weeks of the experiment there were no differences in performance between the two levels of added Ca + P when salt was also used. Between 8 and 12 weeks, pigs fed the higher level grew 17 per cent faster. Although 0.84 + 0.57 per cent Ca + P increased rib Ca and P levels, foot and joint abnormalities showed that these levels were insufficient for normal bone development. This suggests that the Agricultural Research Council estimates of Ca and P requirements for restrictively fed growing pigs are low. TM supplementation did not affect performance when both salt and Ca + P were added to the diet.