The degradation of four different horse feeds in vitro previously evaluated in ponies in vivo

Abstract

Total tract in vivo digestibility values give no information on the manner or site of feed degradation. However, the site and mode of feed degradation may differ between feeds yielding similar nutrient profiles and digestibility values, with potential consequences for equine metabolic health. Here, the course of in vitro fermentation of three subtly different complementary feeds with the same in vivo dry matter (DMD) and gross energy (GED) digestibilities [Winergy Equilibrium High Energy (WEH), Buckeye EQ8 Gut Health (EGH) and Spillers Power Cubes (SPC)] and grass hay was monitored via the evolution of head space gas, to determine between-feed differences in fermentation parameters. In experiment 1, ground feeds (WHOLE) or their residues remaining after incubation with pepsin/HCl and pancreatin (PRE) were incubated with an equine fecal inoculum (F). In experiment 2, feeds were sequentially incubated with digesta from the equine stomach (G) small intestine (SI) and right ventral colon (RVC) all obtained at an abattoir from animals euthanised for non-research purposes. Feed in vitro dry matter digestibilities (IVDMD) were also determined post-incubation with pepsin, pancreatin and F (experiment 1), and after incubation with G, SI and RVC (experiment 2). Incubation with pepsin and pancreatin resulted in substantially elevated IVDMD of all feeds compared with G and SI digesta. The end-point IVDMD of the three complementary feeds incubated with F or RVC were the same within inoculum type. The total gas evolved during the fermentation of HAY with either F or RVC was lower (P < 0.001) than that of the three complementary feeds. EGH yielded less gas and had longer T50 [time taken (h) for evolution of 50 % of total gas] (P < 0.001) than WEH or SPC when incubated with RVC, and yielded (P < 0.001) longer lag and slower fractional rates than WEH and SPC when incubated with F. This suggests that despite the complementary feeds having the same in vivo DMD and GED, EGH was the most slowly fermented by both F and RVC. Such information may help identify which of several apparently similar feeds may be the most suitable for equines prone to nutritionally elicited metabolic disorders, enabling more refined and targeted ration formulation for such animals.