Availability of amino acids for 10- to 20-kilogram pigs: lysine and threonine in soybean meal.

The availabilities of lysine and threonine in soybean meal for 10- to 20-kg pigs were determined in two experiments using slope-ratio methodology. In the first experiment, a basal diet formulated to contain 6 g of lysine/kg, but adequate in all other amino acids, was supplemented with 1, 2, or 3 g of lysine/kg from either soybean meal or L-lysine-HCl. Each of the seven diets was available on an ad libitum basis to six individually penned pigs (barrows:gilts, 1:1) from an initial weight of 9.9 kg until they reached a live weight of 20.8 kg. Daily feed intake was similar among diets. Common-intercept multiple linear regression of daily live weight gain and gain:feed ratio on dietary lysine level indicate slope ratios (soybean meal:lysine.HCl) of .85 and .88, respectively. In Exp. 2, a basal diet formulated to contain 4 g of threonine/kg was supplemented with .65, 1.30, 1.95, or 2.60 g of threonine/kg from either soybean meal or L-threonine. Each of the nine diets was available on an ad libitum basis to six individually penned pigs (barrows:gilts, 1:1) from 9.9 to 21.0 kg live weight. As in Exp. 1, daily feed intake was similar among the nine diets. The slope ratios (soybean meal:L-threonine) from common-intercept multiple regression analyses were .73 and .78 for daily weight gain and gain:feed ratio, respectively. Thus, the availabilities of lysine and threonine in soybean meal for young pigs were estimated to be 85 to 88% and 73 to 78%, respectively.