Estimation of the isoleucine and aromatic amino acid requirements of pregnant swine

The requirements of the pregnant gilt for isoleucine (Ile), total aromatic amino acids (TAAA), phenylalanine (Phe) and the replacement of Phe with tyrosine (Tyr) were investigated in these studies. Five balanced 6 x 6 latin-square arrangements of treatments and time periods were conducted with six pregnant gilts in each trial. Each diet treatment was fed (1.8 kg once daily) for 10 d beginning on d 40 of pregnancy. Nitrogen balance trials were conducted from the 6th to 10th d during each period. Blood samples were obtained from each gilt before and 2 h after the last feeding in each period. Based on the titration trials, the L-Ile requirement was satisfied at .23% of the diet. Assuming that crystalline L-Ile was 100% available, the L-Ile requirement for pregnant gilts fed a corn-soybean meal diet is estimated at .25%. A dietary requirement of no more than .43% satisfied all the criteria measured in the L-TAAA trial. Adjustment for availability of crystalline L-Phe used in the diets would increase the requirement to about .48% dietary L-TAAA. About 42% of the L-TAAA requirement for pregnancy should be supplied by L-Phe.