The Microbiome and Stallion Fertility

Abstract

Equine health and fertility and their relationship to the microbiome are topics of emerging scientific interest. In the sphere of human infertility research, the influence of the semen and gastrointestinal microbiomes on sperm quality and fecundity, as well as the potential for probiotic supplementation to improve male fertility outcomes, have been reported. The overarching aim of this thesis was to contribute to the body of knowledge regarding associations of these two microbiomes in horses (semen and gastrointestinal) with biomarkers of equine fertility, as well as the potential role of prebiotics and probiotics to influence the composition of these microbiomes and sperm quality.

Several new findings regarding the equine gastrointestinal and semen microbiomes were made whilst conducting the three studies reported in this thesis. A small cohort of miniature pony stallions, stabled under the same conditions and fed the same diet and supplement, showed an inter-individual variation in the bacterial composition of their semen microbiomes. Pre-, pro- and synbiotic treatments later administered to the same cohort did not alter sperm quality parameters, nor significantly alter semen or intestinal microbiome profiles; however, safety and tolerability for these supplements was demonstrated with these stallions.

In another cohort of 19 commercial Thoroughbred stallions at stud we explored associations of faecal microbiome measures, with an inflammatory biomarker, in relation to per cycle conception rate (PCCR). While no statistically significant relationships were observed between these criteria, an effect of stud and a trend towards an effect of L-carnitine supplementation was demonstrated on the same fertility outcome. Finally, these findings suggest a need for further research into the effect of nutrition and probiotics on the reproductive and digestive microbiomes of horses of various breeds, with the potential to improve stallion fertility and overall health.