Amino acid supplementation of low-protein sorghum-soybean meal diets for 5- to 20-kilogram swine.

Four growth experiments were conducted to determine the value of added threonine (Thr), methionine (Met), tryptophan (Trp), and isoleucine (Ile) in low-protein, lysine (Lys)-fortified, sorghum-soybean meal diets for starting pigs weaned at 28 d. Trials lasted 28 d and average initial weight was approximately 6.5 kg. A 21% CP (1.15% total and .95% digestible Lys) diet was included in all trials. Basal 15, 17, and 19% CP diets were formulated to contain .95% digestible Lys by adding .38, .26, and .13% Lys, respectively. In Exp. 1, the additions of either Thr (.27%) or Met (.08%) to the 15% CP diet improved (P < .05) ADG and gain/feed (G/F); Trp (.04%) and Ile (.05%) additions had no effect. None of the 15% CP diets resulted in performance comparable to that obtained on the 21% CP diet. In Exp. 2, 19 and 17% CP diets fortified with Thr, Met, and Trp to obtain the digestible contents of the 21% CP diet produced performance equal to performance on the 21% CP diet. Results of Exp. 3 indicate that Thr (.11%) and Met (.08%) supplementation of the 17% CP diet were needed to maximize performance; Trp and Ile additions were not beneficial. Results of the final experiment suggested that Thr and Met additions to the 17% CP diet could be reduced to .05 and .04%, respectively, without lowering performance. These data indicate that a 17% CP, sorghum-soybean meal diet fortified with Lys, Met, and Thr can produce performance equal to that obtained by pigs fed a 21% CP diet.