INFLUENCE OF DIETARY TOTAL SULFUR AMINO-ACIDS AND METHIONINE ON GROWTH-PERFORMANCE AND CARCASS CHARACTERISTICS OF FINISHING GILTS

We conducted three experiments to determine the sulfur amino acid (SAA ) and methionine requirements of finishing gilts. Gilts (PIC Line 326 x C-15, Exp. 1; Line 326 x C-22, Exp. 2 and 3) were blocked by initial weight in randomized complete block designs. In Exp. 1, 64 gilts (ini tially 54 kg) were fed diets containing either .56 or .44% apparent di gestible lysine with increasing SAA levels (63, 70, and 77% of apparen t digestible lysine) in a 2 x 3 factorial. A lysine x SAA interaction (P < .10) was observed for ADG and ADFI. Increasing SAA:lysine ratios from 63 to 70% in diets containing .56% apparent digestible lysine inc reased ADG and ADFI; however, increasing the SAA:lysine ratio in diets containing .44% apparent digestible lysine decreased ADG and ADFI. Pi gs fed .56% apparent digestible lysine had higher (P < .05) ADG and ga in:feed ratio (G/F) and lower 10th rib fat depth than pigs fed .44% ap parent digestible lysine. Increasing the SAA:lysine ratio had no effec t on G/F or carcass characteristics. In Exp. 2, 80 gilts (initially 74 kg) were fed diets containing .225, .25, .275, .30, or .325% apparent digestible SAA (45, 50, 55, 60, or 65% of .50% apparent digestible ly sine, respectively). Increasing SAA concentrations decreased ADG and G /F (linear, P < .06). In Exp. 3, 105 gilts (initially 72 kg) were fed diets containing .20% apparent digestible cystine and .10, .125, or .1 5% apparent digestible methionine (20, 25, or 30% of .50% apparent dig estible lysine). Increasing digestible methionine increased ADG, ADFI, plasma methionine concentrations (linear, P < .01), and G/F (quadrati c, P < .03). The greatest increases in ADG and G/F were observed when apparent digestible methionine was increased from .10 to .125%. Based on these results, the apparent digestible methionine requirement is no greater than 25% of apparent digestible lysine, in diets containing e xcess cystine. This equates to an apparent digestible SAA:lysine ratio that is no greater than 50%.