Effects of feeding soybean meal with varying trypsin inhibitor activities on growth of fingerling channel catfish

Uncooked hexane extracted soybean meal was heated for various lengths of time to produce meals with varying trypsin inhibitor activities. Fingerling channel catfish (Ictalurus punctatus) were fed 25 and 35% crude protein practical type test diets containing soybean meal with graded levels of trypsin inhibitor activity for 10 weeks. Growth rates and protein efficiency ratio (PER) values were reduced in fish fed raw and inadequately heated soybean meal at both protein levels. These effects were more severe at the lower dietary protein level. Growth rates and PER values improved in each study as the trypsin inhibitor activity of the soybean meal decreased to tolerable levels. Fish fed the 35% crude protein diets appeared to tolerate soybean meal with much higher trypsin inhibitor activity than fish fed the 25% crude protein diets. Even though growth rates and PER values were not significantly different over a rather wide range of dietary trypsin inhibitor activities, the best growth rates were not observed at either protein level until about 83% of the trypsin inhibitor activity in the soybean meal had been destroyed.