Systemic heat stress is detrimental to sperm production and male fertility but this phenomenon has not been adequately examined in the horse, or in field settings relevant to the Australian Thoroughbred industry. Specifically, we do not know how the climatic conditions experienced by stallions affect their fertility, nor how projected increases in temperature associated with climate change might affect the industry's productivity in the future.To address these issue this project aims to answer the following questions: (i) Do ambient temperatures affect fertility of Thoroughbred stallions and induce oxidative damage in stallion sperm DNA?; (ii) Which parts of the equine genome are most susceptible to heat stress induced DNA damage?; (iii) Can management measures be implemented to alleviate the effects of heat stress on thoroughbred stallions?; and (iv) Can an antioxidant supplement formulated to protect spermatozoa from oxidative stress be beneficial in susceptible animals? Understanding these mechanisms should yield several short term outcomes improving the reproductive efficiency of the Thoroughbred industry, with a longer term outlook of development of novel management strategies to alleviate the effects of heat stress on fertility.