DIGESTIBLE THREONINE REQUIREMENTS OF STARTER AND FINISHER PIGS

The digestible threonine (Thr) requirements of starter (28 d of age initially, 6 to 16 kg) and finisher (58 to 96 kg) pigs were determined. Each growth trial evaluated control and basal diets and the basal diet plus four incremental additions of L-Thr (.60 to .76% dietary Thr for starter pigs and .30 to .50% dietary Thr for finisher pigs). The basal diet fed to starter pigs contained 17.6% CP and 1.25% lysine and was based on sorghum, peanut meal, soybean meal, and dried whey. The basal diet fed to finisher pigs contained 9.7% CP and .75% lysine and was based on sorghum supplemented with lysine, methionine, tryptophan, and isoleucine. Incremental increases in dietary Thr increased (P < .05) ADG and ADFI of starter pigs quadratically. Gain/feed increased (P < .01) linearly. Based on broken-line regression analyses, .63% Thr maximized ADG of starter pigs. Daily gain an gain/feed of finisher pigs increased linearly (P < .0) and quadratically (P < .01) as dietary Thr content increased. Broken-line regression analyses determined that .41% Thr maximized ADG and gain/feed. Digestion trials with pigs fitted with an ileal T-cannula determined that the basal starter and finisher diets contained .43 and .17% apparent ileal digestible Thr and 3.35 and 3.38 Kcal of fecal DE/g, respectively. On average, crystalline Thr had an apparent ileal digestibility of 98%. Based on these values and the total Thr requirements given above, the digestible Thr requirement of finisher pigs for maximum ADG and gain/feed was estimated to be .28%. The ADG of starter pigs was maximized at .46% digestible Thr, but gain/feed was not maximized within the range of Thr fed.