The effect of diets containing soybean meal, soybean protein concentrate, and soybean protein isolate of different oligosaccharide content on growth performance and gut function of young turkeys.

An experiment was conducted to investigate the effects of diets containing soybean meal (SBM), soybean protein concentrate (SPC), and soybean protein isolate (SPI) on growth performance and gut function of the young turkey. A total of 812 one-day-old male turkey poults were randomly assigned to 4 dietary treatments, with 7 pens per treatment and 29 birds per pen. The 4 experimental diets contained SBM, SBM-SPC, SPC, and SPI and were fed throughout the two 4-wk experimental periods. In each period, the diets were isonitrogenous and isocaloric and contained similar amounts of total and water-soluble nonstarch polysaccharides. The content of oligosaccharides differed among the diets and averaged 2.4, 1.9, 0.9, and 0.1% for SBM, SBM-SPC, SPC, and SPI, respectively. When compared with SBM, birds consuming the SBM-SPC and SPC diets had higher (P<0.05) final BW (4.32 vs. 4.45 and 4.46 kg, respectively). Incorporation of SPI as a substitute for SBM resulted in improved (P<0.05) feed utilization (from 1.76 to 1.67) but did not affect the final BW. Significant changes in cecal concentrations of short-chain fatty acids were observed and averaged 130, 103, and 89 micromol/g of digesta for the SBM, SBM-SPC, and SPC diets, respectively. This coincided with the proportional decrease in dietary oligosaccharide content (from 2.4 to 0.9%) and was further substantiated by a significant decrease in ileum weights. Feeding the SPI diet resulted in the lowest ileal and cecal tissue weights as well as the lowest cecal short-chain fatty acids concentration. There was no effect of diet on digesta pH, viscosity, and mucosal sucrase and maltase activities. Bacterial beta-glucuronidase activity was decreased (P=0.08) in the cecum (from 0.98 to 0.60 U/g) with decreased dietary oligosaccharide content. In conclusion, partial or almost complete substitution of SBM with SPC suppressed the fermentation processes in the ceca but enhanced the growth rate. Substitution of SBM with SPI significantly improved feed utilization but decreased BW of 4-wk-old turkeys with no effect on growth rate of older 8-wk-old birds.