HIGH-PROTEIN AND LOW TRYPSIN-INHIBITOR VARIETIES OF FULL-FAT SOYBEANS IN BROILER CHICKEN STARTER DIETS

Two broiler growth trials of randomized block design were conducted to evaluate the nutritional quality of two new varieties of full-fat soybeans (SB) in starter diets. Use of the high protein (HP) SB (44% CP) has the potential to replace conventional soybeans in poultry rations and reduce the amount of SB needed. Use of the low-trypsin inhibitor (LTI) SB may eliminate the cost of heat treatment before feeding to poultry. The protein sources were raw SB (39% CP, 70 Trypsin Inhibitor Units (TIU) g-1 DM), autoclaved SB, autoclaved HP SB, LTI (42 TIU g-1 DM) and commercially roasted SB. Diets were formulated to be isonitrogenous and isoenergetic. Supplementation of diets with 0.3% DL-methionine was also studied, as the antiproteolytic activity of the TI makes sulphur amino acids less available for growth. Mean body weight gains, feed efficiency, dry matter and crude protein digestibilities and total carcass protein and energy content of the chickens fed HP, autoclaved or roasted SB were superior (P < 0.05) to those fed the raw SB diet. Performance of the chickens fed the HP SB diet was similar to those on the roasted SB diet. Growth and feed conversion of chicks fed the LTI diet were similar to those fed the raw SB diet. However, mean pancreas weights of the chicks fed LTI were lower (P < 0.001) than those fed raw SB which could be due to the lower trypsin inhibitor activity of the LTI beans. Chickens given the methionine supplemented LTI diet made greater weight gains (P < 0.05) than those on the nonsupplemented diet. Heat treatment is required for the LTI beans. Full-fat HP soybeans may replace conventional soybean meal in broiler chicken starter diets if the formulation is adjusted for the differences in their protein and fat contents.