The present experiment had two purposes: (i) to study crystalline amino acid supplementation to crude protein-reduced diets, and (ii) to study the effect of different isoleucine (Ile) to lysine (Lys) and valine (Val) to Lys ratios in diets for young pigs. A total of 145 pigs were weaned at 28 days and fed one of 5 diets for a total of 4 weeks. Two basal diets were formulated to provide crude protein in levels either as recommended (positive reference diet, PRD), or below recommendations (negative reference diet, NRD). The basal diets contained 95% of recommended Lys, and all other essential amino acids were provided proportionally to Lys. The NRD diet contained 0.53 Ile and 0.61 Val relative to Lys. This diet was supplemented with either Ile (0.61 of Lys) or Val (0.72 of Lys), or both Ile and Val, in order to make up the 5 diets. Supplementation with Ile to the NRD diet did not improve (P>0.05) average daily gain (ADG) and feed conversion ratio (FCR), whereas supplementation with Val or both Ile and Val improved ADG (P=0.02) and FCR (P=0.03). By adding either Val or both Ile and Val to the crude protein-reduced diets, both ADG and FCR could be maintained at the same level as for the pigs fed the PRD diet. These results indicate that Val is limiting before Ile, when reduced relative to Lys. By supplying crystalline amino acids, dietary crude protein can be reduced without negative effects on animal performance.
Animal Feed Science and Technology, 2009, Vol 154, p. 248-253