Results of a Clinical Trial Showing Changes to the Faecal Microbiome in Racing Thoroughbreds after Feeding a Nutritional Supplement.

Next-generation sequencing (NGS) has been used to evaluate the effect of various interventions on the equine microbiome. The aim of this randomised blinded clinical trial was to determine if a prebiotic nutritional supplement would result in a change from baseline in the faecal microbiome composition of racing Thoroughbred horses in training being fed a high concentrate/grain-based diet to be more similar to that found in forage fed/pasture grazed horses. Thirty-two horses on one training yard were randomised to either receive the supplement or not. Faecal samples were collected at baseline, 6 and 12 weeks for NGS of the 16S ribosomal subunit gene. Twenty-two horses completed the trial, met the inclusion criteria and were included in the intention to treat analysis; 20 horses were included in the per protocol analysis. The mean and median percent decreases in , increases in and the ratio were significantly greater than zero for the treated horses only. Supplemented horses (8/10) were more likely than control horses (2/10) to show an increase in of a ≥9% with ≥24% increase in , ≥5% decrease in , ≥16% increase in the F:B ratio and ≥2% increase in (RR = 4, 95% CI: 1.1-14.4, = 0.01). This provides useful information for further investigations on long-term effects on the microbiome and on health and racing-related outcomes.