Project snapshot: Reducing the effects of heat stress and ageing on sperm DNA in Thoroughbred stallions

Thoroughbred stallion fertility drives breeding success in Australia; however, conception rates remain modest and often fall with age and heat.

This project examined how oxidative stress damages sperm DNA and affects fertilisation, embryo growth and foal performance. To address this, researchers used lab tests, field monitoring and a controlled nutrition trial. They assessed semen quality, climate effects and long-term progeny outcomes.

Overall, results showed that oxidative stress is the main cause of sperm DNA damage. In particular, heat and ageing increased this stress and reduced fertility. Consequently, the study identified practical tools for industry use. The halo assay and sperm chromatin structure assay suit routine screening, while the comet assay detects finer damage in research.

About 20% of stallions showed high sensitivity to heat and clear fertility loss under high temperature–humidity index (THI) conditions. The team also developed a horse-specific THI to predict risk periods.

In addition, targeted nutrition improved outcomes. L-carnitine and NTFactor® Lipids strengthened sperm membranes and improved resistance to stress. As a result, studs can identify at-risk stallions earlier and manage heat impacts more effectively.

These tools can lift pregnancy rates, extend breeding careers and improve industry productivity.