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

Overview

• This study evaluated how different types and amounts of tannins affect gas production and nitrogen waste during fermentation in the horse cecum, using in vitro experiments.
• Its goal was to explore dietary strategies to reduce methane emissions and nitrogen waste from horses, which are important for lowering the environmental impact of animal agriculture.

Research Context and Objectives

• Animal agriculture contributes to greenhouse gas emissions and nitrogen waste, raising environmental concerns.
• Tannins, plant compounds found in some feeds, have been shown in ruminants to reduce methane production and improve nitrogen retention.
• The study aimed to assess whether hydrolysable tannins (from chestnut) and condensed tannins (from mimosa) can similarly affect fermentation by microbes in the equine cecum.
• This was done by measuring gas accumulation, volatile fatty acids, and ammonia in controlled in vitro fermentation experiments with graded tannin levels.

Methods

• Two separate in vitro experiments were conducted, each with three replications per treatment to ensure reliability.
• Test substrate: 0.2 g of alfalfa as the fermentation substrate.
• Tannin treatments included adding 5%, 10%, 15%, and 20% (weight/volume) of either chestnut (hydrolysable tannin) or mimosa (condensed tannin) tannin extract.
• Variables measured included total gas and hydrogen accumulation, methane levels, volatile fatty acids (acetate, propionate, butyrate), and ammonia concentration.

Key Findings

• Both tannin types reduced total gas and hydrogen accumulations during fermentation, by up to 27% and 82%, respectively, relative to control without tannins.
• Mimosa tannins significantly decreased methane accumulation by 4% to 83%, whereas chestnut tannins did not affect methane levels.
• Acetate production was reduced by mimosa tannins by up to 36%; chestnut tannins had no effect on acetate levels.
• Neither tannin type influenced butyrate accumulation.
• Both tannins increased propionate levels by up to 38%, which is often associated with more efficient fermentation and lower methane production.
• Ammonia accumulation, indicating nitrogen waste, was markedly decreased by 96% with chestnut tannins and 87% with mimosa tannins, signifying improved nitrogen retention.

Conclusions and Implications

• The study demonstrates that both hydrolysable and condensed tannins can reduce gas production and significantly lower nitrogen waste during equine cecal fermentation in vitro.
• Only condensed tannins (from mimosa) showed a significant capacity to decrease methane production.
• These effects suggest that dietary inclusion of tannins could be a promising approach to mitigate environmental impacts related to methane emissions and nitrogen waste in horses.
• Further in vivo studies are needed to confirm these findings within living animals and evaluate potential impacts on animal health and performance.
• Overall, this research supports the strategic use of tannins as an environmentally beneficial additive in equine nutrition.