63 The effect of dietary probiotics in actively racing Standardbred horses receiving oral antibiotics

Abstract

Horses are hindgut fermenters with a highly complex microbiome populating the cecum and colon. This microbiome contributes an abundance of physiological functions to the host, including immune stimulation, defense against pathogens, neutralization of toxins, and regulation of gene expression in epithelial tissues. During bouts of infectious disease, antibiotic administration can disturb this microbiological environment, leading to adverse effects such as colitis and acute diarrhea. Horse owners often provide probiotics to horses receiving antibiotics in an attempt to protect against these adverse effects despite a lack of evidence for their efficacy. Thus, the purpose of the current study was to evaluate the effect of probiotics in horses receiving concurrent antibiotic treatment. Sixteen actively racing Standardbred horses were randomly allocated to one of 4 treatment groups [Antibiotics (A; Sulfadiazine/Trimethoprim), Probiotics (P; Herbs for Horses PROBIOPlus Ⓡ , Herbs for Horses, Guelph ON), A+P, or control (C)] in a 4-way crossover design. A and A+P horses received antibiotics from Day 0–10, P and A+P received probiotics from Day 0–28, and C horses received the same diet with no probiotic or antibiotic for 28 d. Fresh fecal samples were collected on days −1, 0, 1, 2, 9, 10, 11, 28, 29 and 30 from each horse. Analyses include fecal dry matter (DM; %), fecal pH, and fecal scores (FS; 0 – 9) were measured on all fecal samples. Data were analyzed using a 2-way RM-ANOVA (SigmaPlot Version 12) with fixed effects as horse, trial, day, and treatment and random effects as the intercept for the crossover design. Significance was accepted at P < 0.05. Fecal score in C horses (2.6 ± 0.3) was higher than in A+P horses (1.9 ± 0.2) on Day 10 ( P = 0.04); FS of C horses (2.7 ± 0.3) was also higher than P horses (1.6 ± 0.3) on Day 9 ( P = 0.02). Fecal DM was lower in C horses (26.9 ± 2.5%) than A+P horses (30.3 ± 2.5%; P = 0.03) overall, but there were no differences at any individual time point. Fecal pH was higher in C horses (6.6 ± 0.04) than P horses (6.5 ± 0.04; P = 0.008) and A+P (6.4 ± 0.04) overall; on Day 9 and 10, pH was lower in A+P (6.3 ± 0.1 and 6.2 ± 0.1, respectively) than C horses (6.7 ± 0.1 for both days). The antibiotic treatment had no differences on dry matter or pH between treatments. Interim results demonstrate that treatment with A+P is associated with an increase in fecal DM and concomitant reduction in FS. Fecal pH is reduced in horses receiving P and A+P. The practical implications of these data are as yet unclear but will be clarified upon completion of microbiome analysis which is currently ongoing.