Changes in Faecal Bacteria Associated with Concentrate and Forage-only Diets Fed to Horses in Training

Reasons for performing study: Diets rich in readily fermentable carbohydrates, fed traditionally to meet the increased energy requirements of the performance horse, are associated with a number of gastrointestinal disorders that involve disturbances in the intestinal microbiota, however, these changes are poorly understood.

Objectives: With the long-term objective of improving intestinal health and to increase understanding of the relationship between diet and microbiota, the effect of feeding Standardbred horses a high-energy forage-only (F) diet was studied compared to a more traditional forage-concentrate (C) diet on faecal microbiota.

Methods: Diets were fed in a cross-over design to 6 mature geldings on a scheduled training regime, both periods consisting of 29 days. DNA was extracted from faecal samples collected at 4 time points from each period, bacterial 16S rRNA genes were amplified and community composition assessed by terminal-restriction fragment length polymorphism, cloning and sequencing. Faecal pH and cultivable lactic acid bacteria (LAB) and enterobacteria were also assessed on the final collection day of each period.

Results: Diet F resulted in a microbial composition that was more stable between sampling periods and had lower counts (P<0.05) of cultivable lab and specifically members of the streptococcus bovis/equinus complex. motile and swarming lactobacillus ruminis was present in all horses on diet c and not in horses on diet f. diet c also resulted in the increase (p<0.05) in members of clostridiacea cluster iii and a concomitant reduction (p<0.05) in an unknown group of bacteroidales.

Conclusions and potential relevance: The greater microbial stability and reduction in LAB and members of the Streptococcusbovis/equinuscomplexon diet F indicate an opportunity to develop feeding strategies that support equine health and welfare. Novel changes identified in the faecal microbiota that resulted from carbohydrate inclusion merit further investigation.