Digestibility and ruminal digestion of non-nitrogenous compounds in adult sheep and goats: Effects of chestnut tannins

Abstract

This study investigates effects of hydrolysable tannins on in vivo digestibility and ruminal digestion. Chestnut extract (110 g) was sprayed onto 1 kg of hay feed (H10 diet) (80 g kg −1 chestnut tannins). H10 and control diets (hay without tannins, H0 diet) were tested (2 × 2 Latin square) on six sheep and six goats fed once daily at maintenance level. Half the animals had a rumen cannula. Ruminal pH and volatile fatty acid (VFA) concentrations were recorded during a 12 h post-feed period. Tannins significantly decreased dry matter (DM) and organic matter (OM) apparent digestibilities, from 63.3% to 57.7% in sheep and from 63.8% to 60.7% in goats. Animal live weight and body condition score were not affected. Rumen in situ degradabilities of H10 and H0 were measured for each diet (H0 and H10) fed to both types of animal. The four DM degradation kinetics were similar for both species. Microbial nitrogen supply was estimated by the quantity of purine derivatives in urine, and was found not to be modified by tannins, thus indicating that ruminal microbial synthesis had not been disturbed. Daily evolution of ruminal VFA total concentration and molar composition were unchanged, although in goats pre-feed total VFA concentration was 39.9 mM with H10 and 54.7 mM with H0. Differences in daily pH evolution were observed for both animal species: pre-feed pH values were the same for both diets, but the decrease in pH stopped 1–3 h post-feeding with H10, and 9–12 h with H0. The minimum pH varied between 6.3 and 6.5 in the tannin-rich diet compared with 6.0 in the tannin-free diet. Although chestnut tannins were responsible for lower digestibilities of DM, neutral detergent fibre and acid detergent fibre fractions, they did not disturb rumen degradation of cell wall or ruminal microbial synthesis.