Comparative effects of dietary tannins in ducks, chicks, and rats

Studies were conducted to compare the effects of feeding high-tannin sorghum (HTS)- and low-tannin sorghum (LTS)-based diets suboptimal in protein to ducks, chicks, and rats. In the first series of experiments, Savanna (HTS) depressed both growth and feed efficiency of chicks and rats when compared with animals fed RS-610 (LTS). In contrast, ducks fed Savanna-based diets exhibited greater weight gains, but poorer feed efficiency values than birds fed RS-610. In a second series of experiments, Pioneer 8333 (LTS) and DeKalb BR-64 (HTS) sorghum-soybean meal diets were fed to chicks, ducks, and rats. As compared with animals fed 8333, BR-64 depressed both growth and feed efficiency of chicks and rats, but did not significantly affect either parameter in ducks. The lack of effect of HTS on duck growth may have been due to the formation of tannin-protein complexes upon exposure of the ground grain to water. This theory was based on the following observations: 1) ducks consumed water immediately after eating to facilitate swallowing the dry-mash diet; 2) a large amount of feed was deposited on the bottom of each water trough and subsequently consumed; and 3) ground HTS, which had been soaked for 4 h, had virtually no assayable tannin after drying. However, despite the marked reduction in assayable tannin content of treated HTS versus HTS that was dried only, the former material still depressed growth and feed conversion of rats. Thus, the lack of a growth-depressing effect of sorghum tannins in ducks fed dry-mash diets is both unique and unexplained.