D-ALLOTHREONINE HAS NO GROWTH-PROMOTING EFFICACY FOR CHICKS

One hundred and sixteen crossbred male chicks were used in two battery trials to establish the biological efficacy and toxicity of D-allothr eonine (Dallo-Thr) relative to L-Thr. In the efficacy trial, graded do ses of D-allo-Thr or L-Thr were added to a Thr-deficient (0.24% L-Thr) chemically defined diet and fed to chicks during the period 10 to 21 d posthatching. Addition of 0, 0.09, and 0.18% L-Thr produced marked l inear (P < 0.01) growth and feed efficiency responses, but addition of 0.18 or 0.36% D-allo-Thr did not elicit a response in either weight g ain or feed efficiency. In the toxicity trial, 2% D-allo-Thr or 2% L-T hr were added to a conventional 23% CP corn-soybean meal starter diet. During an 11-d feeding period, neither weight gain nor voluntary feed intake were affected (P > 0.10) by 2% additions of either compound. T his experiment demonstrates that chicks cannot metabolize D-allo-Thr t o L-Thr and that neither L-Thr nor D-allo-Thr are growth depressing wh en provided in a large surfeit.