Diet related changes in the gastrointestinal microbiota of horses :

Abstract: Naturally horses were used to survive on grazing a fibre rich diet and consequently their energy metabolism was dependent on fibre degrading microorganisms inhabiting their gastrointestinal tract. However, modern performance horses are exposed to high intensity training, therefore energy-dense feedstuffs had to be introduced to feed rations to meet their high energy requirements. These changes in the diet resulted also in changes in the microbial ecosystem inhabiting the gastrointestinal tract which may also have consequences for the health of the horse. The aim of this study was to gain a better understanding about diet related changes within microbial populations in the equine gut using both culture based and molecular methods. Six mature geldings were fed two different diets (haylage-only and haylage-concentrate) in a cross-over design, both periods consisting of 29 days. Faecal samples were used for the culturing work on Rogosa and VRBG plates, for pH measurement and for analysis with T-RFLP. Several bacteria isolated from plates of both diets were identified by sequencing of 16S rRNA. The switch to a diet comprising concentrate to 50% of DM resulted in a significant increase in abundance of lactobacilli and streptococci, and in the appearance of Lactobacillus ruminis, previously not detected in horse. Several other organisms were also significantly affected by the diet as indicated by T-RFLP results. However, identification of some TRFs is inhibited by the lack of knowledge and references in open databases. On the contrary, an effect of diet on numbers of enterobacteria, faecal pH and diversity of the microbial population could not be observed. The results of this study show that there are diet related changes in horses' gastrointestinal microbiota, indicating that their ecosystem is affected by the diet. Similar patterns could be observed in most of the horses, but also individual differences exist. However, our knowledge is still limited on horses' gastrointestinal microbiology. Therefore further investigations are needed to gain a better understanding of the interactions between gut microbiota and different feeding practices which would help to develop feeding strategies that can support equine health and welfare.