Condensed tannins are only partially responsible for variations in nutrient digestibilities of sorghum grain cultivars

Nitrogen-corrected true metabolizable energy (TME_n) and true amino acid digestibility values were determined, using cecectomized cockerels, for 20 sorghum [Sorghum bicolor (L.) Moench] cultivars that ranged in catechin equivalent (CE) percentages from 0 to 3.88. There were significant (P ≤ 0.01) overall inverse relationships between CE content and (1) the individual digestibilities of lysine, methionine, threonine, isoleucine, leucine, valine, phenylalanine, histidine, and arginine; (2) the mean digestibility of essential amino acids; (3) the mean digestibility of nonessential amino acids; and (4) TME_n values. In contrast to these overall trends, several cultivars of similar condensed tannin content had markedly different nutrient digestibilities. The dissimilarity of protein digestibilities in sorghum genotypes of similar tannin content was confirmed by subjecting samples of the ground grains to in vitro pepsin digestion with subsequent visualization of the undigested proteins by SDS-PAGE. The present work suggests that other components besides tannins are responsible for variations in the availability of nutrients in sorghum.