Investigations of Threonine Requirements of Broiler Chicks Fed Diets Based on Grain Sorghum and Soybean Meal

Three trials were conducted to estimate the threonine (Thr) requirement of male broiler chicks. Chicks 7 days of age were fed a grain sorghum-soybean meal diet containing .59% Thr, supplemented with 0, .05, .09, .15, .22, .27, or .28% L-Thr. Levels of basal and supplemental amino acids were confirmed by ion-exchange chromatography. Diets were fed for 18 or 20 days, depending upon the trial. A corn-soybean meal diet analyzed to contain .90% Thr was used for comparison. Results of the three trials were pooled for determination of Thr requirements. A significant improvement in gain was observed when the basal grain sorghum-soybean meal diet was supplemented with .09% supplemental Thr (total .68% Thr). No further improvements in gain were observed at higher levels of Thr supplementation. Body weight gain of chicks fed the Thr-supplemented diets did not differ significantly from that of chicks fed the corn-soybean meal control diet. For maximum feed utilization, the Thr requirement was .79%, as estimated by regression analysis. This is in agreement with the .80% requirement suggested by the National Research Council in 1984. Feed utilization of chicks fed the corn-soybean meal diet was significantly better than that of chicks fed any of the grain sorghum-soybean meal diets regardless of the level of Thr supplementation.