Background: Commercial horse feeds use cereal grains and by-products; however, their effects on the caecal environment remain poorly characterised.
Objective: Characterise the effect of commonly used feed ingredients on caecal pH and volatile fatty acid (VFA) concentration.
Study design: 6 × 6 Latin square.
Methods: Two days prior to the start of the study, 6 caecally cannulated Quarter horses were moved into individual stalls where Smooth bromegrass hay (brome) was offered at 2.0% BW/d split between 2 feedings (0600 and 1800). On day 0, caecal digesta was collected every 2 h for 12 h relative to the 0600 feeding to establish control values for horses consuming only brome (HAY). On day 1, horses began consuming their respective treatments which consisted of beet pulp (BP), maize (M), dehydrated alfalfa (A), oats (OAT), soybean hulls (SBH), or wheat middlings (WM) at 0.25% BW/d split into 2 feedings. On day 7 of each treatment period, caecal digesta was collected every 2 h for 12 h and analysed for pH and VFA. Data were analysed using mixed ANOVA with repeated measures, fixed effects of treatment and time and random effects of horse and period.
Results: There was a main effect of hour (P ≤ .05) indicative of post-prandial shifts in caecal metabolites. There were no main effects of treatment on pH or VFA concentration (P ≥ .3). Effects of hour × treatment (P ≤ .04) were observed for all response variables. Regardless of treatment or hour, caecal pH remained well within normal limits. Three horses exhibited signs of lower oesophageal choke immediately after consumption of BP pellets.
Limitations: Interactions between ingredients when mixed for formulation of a concentrate warrant further research. Furthermore, a short adaptation period was chosen to mimic common management practices.
Conclusion: Minimal differences in caecal fermentation parameters were detected when ingredients were fed at a common inclusion level.
Keywords: caecum; fermentation; fibre; horse; volatile fatty acids.
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