Digestion in the pig between 7 and 35 d of age. 1. The performance of pigs given milk and soya-bean proteins.

1. One hundred and fourteen pigs between 7 and 35 d of age were given diets containing milk or soya-bean proteins in four separate experiments. 2. The substitution of milk protein by soya-bean meal (SBM) to 75% of the total dietary protein reduced the weight gains and food conversion efficiencies of the pigs by 85% between 7 and 14 d of age and 31% between 21 and 28 d of age. 3. The treatment of soya-bean protein with alkali did not improve the performance of the pigs. 4. The substitution of milk protein by two different isolated soya-bean proteins (ISP) resulted in weight gains of 34 and 60% of te gains of pigs given milk protein diets. 5. Supplementation of the soya-bean-protein diets with methionine to 13 . 7 g/kg (5 g/16 g nitrogen) resulted in reduced food intakes and weight gains of the pigs and a 20-fold increase in the concentration of methionine in the blood plasma. 6. Supplementation of soya-bean-protein diets with lysine to 22 g/kg (8 g/16 g N) in addition to methionine doubled the concentration of lysine in the blood plasma. 7. The apparent digestibility (AD) of dry matter (DM) and N of the diets containing soya-bean protein increased with increasing age of the pigs, but the AD of the milk-protein diet was not affected by the age of the pigs. The retention of N as a percentage of the N intake increased from 57--67% for soya-bean protein over the duration of the experiments while the average value for the milk-fed pigs was 85% at all ages. 8. At 35 d of age, the fat content of the carcasses of the pigs given the ISP diet was 249 g/kg DM compared to 164 g/kg DM for the pigs given the milk diets.