In vivo effects of dietary sorghum tannins on rabbit digestive enzymes and mineral absorption

This study demonstrates the extent of the in vivo inhibitory action of two levels of dietary sorghum tannins on rabbit digestive enzymes as well as mineral absorption. Addition of low-tannin (1.4% catechin equivalent) sorghum grains to the animals diet did not significantly change growth rate, food consumption, or feed conversion ratio. However, addition of high-tannin (3.5% catechin equivalent) sorghum grains significantly reduced their live body weight gain, feed conversion ratio, and slightly increased food consumption with respect to the control. The activities of alpha -amylase, trypsin and lipase in digesta. obtained from the upper part of the small intestine were inhibited in animals fed on sorghum grains. Inclusion of low- and high-tannin sorghum grains inhibited alpha -amylase by 37% and 77%, trypsin by 22% and 56% and lipase by 6% and 43%, respectively. Estimation of apparent calcium and magnesium absorption revealed a decrease in the calcium, but not magnesium, absorption only in animals fed high-tannin sorghum grains. Our in vivo results show a significant effect for ingested dietary sorghum tannins on their first target i.e. the digestive tract, as well as indicating though crudely (increased corrected liver weight) the possible toxic effect of sorghum tannin. The lack of toxicity in animals fed low-tannin sorghum grains may suggest the existence of a threshold-limit. (C) 2001 Elsevier Science Inc. All rights reserved.