Impact of hydrolysable and condensed tannin sources and levels on in vitro equine cecal fermentation.

Abstract: Environmental impacts of animal agriculture are under intense scrutiny, thus strategies to decrease greenhouse gas emissions and volatile nitrogen waste are valuable. As dietary inclusion of tannins has been shown to decrease methanogenesis and improve nitrogen retention in ruminants, this study was designed to determine the effects of graded levels of hydrolysable tannin (chestnut) and condensed tannin (mimosa) on equine in vitro cecal fermentation. Methods: Two in vitro experiments were conducted, each with three replications per treatment. Treatments were 0.2 g alfalfa without or with 5, 10, 15, or 20 % (wt/vol) chestnut or mimosa tannin. Both tannins decreased (P < 0.01) total gas and hydrogen accumulations by as much as 27 and 82 %, respectively, when compared to accumulations in nontreated controls (11 mL and 0.34 μmol/mL incubation fluid). Results: Mimosa, but not chestnut, treatments decreased (P < 0.01) methane accumulations, with decreases ranging from 4 to 83 % compared to controls (1.1 μmol/mL). Mimosa, but not chestnut, treatment decreased acetate accumulations by as much as 36 % compared to controls (14.8 μmol/mL) but neither tannin affected accumulations of butyrate (1.6 μmol/mL). Both tannin treatments increased (P < 0.05) propionate accumulations by as much as 38 % compared to controls (5.7 μmol/mL). Ammonia accumulations were decreased by as much as 96 and 87 % by chestnut and mimosa treatments, respectively, compared to controls (0.24 μmol/mL). Conclusions: These results indicate tannins may effectively reduce volatile nitrogen waste and methane emissions in equids and thus warrant further research to validate these results in vivo.