A new study analysed the impacts of heat stress on Australian Merinos in an artificial breeding trial. File photo.

Heat stress hits fertility

Sheep study shows overheating spurs reproductive wastage

A study into reproductive wastage in Australian Merino sheep found summer heat stress can have a significant impact on breeding success.

Western Sydney University School of Health and Science researcher Dr Edward Narayan was lead author of the study, which was based on analysis of the measured physiological stress of sheep in an artificial breeding trial at Dubbo in 2015-16, when temperatures hit 40 degrees Celsius.

“Heat stress is believed to reduce embryo production during the artificial insemination process, because the physiological and cellular aspects of reproductive function and early embryo development are disrupted,” Dr Narayan said.

Stress-indicating hormone levels were sampled in the sheeps’ faeces samples, measured against body and ambient temperatures and then matched against fertilisation results in the AI trial.

“In our study, ewes that had higher recorded temperatures had a significantly lower percentage of transferable embryos,” said Dr Narayan, who leads Western Sydney University’s Stress Lab.

“We hope this study will help with adjustment of flock management to reduce stress. Any loss of lambs is a big dollar impact for producers.

“My ambition is to add value to real world. I do producer focused research, where science can help industry.”

While the study demonstrates a link between heat and physiological stress and reduced fertility in the Merinos, it was not possible to define set ratios of the impact on fertilisation success.

“Ewes that had higher recorded temperatures had a significantly lower percentage of transferable embryos,” Dr Narayan said.

“There are no hard numbers on the impact of heat on fertilisation rates, because every animal is different and some are more resilient than others.”

Future research will flow from the study, targeting methods to minimise the impact of heat on fertilisation rates including, particularly flock management in the finishing period of the last month or so before new lambs are due.

“You have to look at it from the animal’s point of view. Monitoring stress quickly and reliably will assist with better flock management,” Dr Narayan said.

“Food, water, nutrition are the most important factors, it comes down to the basic.”

Future research plans also include investigating epigenetics, that is the potential for mother ewes to pass on impacts from heat stress to their foetus.

“Living in a hot environment there are some modifications to DNA that lead to genetic impacts. That may mean lambs carry non-productive genes, or vice-versa.”

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