With climate change driving more frequent and intense heat events, researchers are tackling a key concern for Australian sheep producers: how to maintain flock fertility and welfare during summer joinings.
Led by Assoc. Professor Will van Wettere, The University of Adelaide, with support from the South Australian Drought Resilience and Adoption Hub (The SA Drought Hub), industry partners, five Grower Groups, the Northern and York Landscape Board, and the South Australian Research and Development Institute (SARDI); the research arm of Primary Industries and Regions SA), the team investigated whether supplements such as melatonin (Regulin®) and vitamin ADE can protect ewes from the negative impacts of heat stress during mating and pregnancy.
“Previous research has shown that each day above 32°C during mating can reduce lambing rates by 3.5%,” said Assoc. Prof van Wettere.
The project, running from November 2023 to July 2025, involved 29 producer sites across SA and tested four treatment groups: no supplementation, melatonin only, ADE only, and a combination of both. Treatments were administered just before joining.
Results averaged across two summer joinings (2023/24 and 2024/25) show that melatonin significantly improved reproductive outcomes.
“Melatonin implants resulted in a 2.3% increase in pregnancy rate and an 8.7% increase in twinning rate. There was a 12% increase in the number of fetuses scanned per ewe joined. The combined treatment of melatonin and ADE performed slightly better, boosting pregnancy rates by 2.89% and lifting foetal numbers by 13.41%. However, vitamin ADE alone did not yield any significant improvements in fertility,” he explained.
Supplementing ewes with melatonin before joining may be a viable tool to support flock productivity in a warming climate.
SA Drought Hub Knowledge Broker Tony Randall says that the findings are of great interest to livestock producers.
“Through Hub support the research team were able to promote the findings via Grower Groups and Landscape Board members, and their extensive grower networks. The research provided valuable insights into how to help mitigate the impacts of heat stress on breeding success,” he said.
“The local field days, which were arranged by the Grower Group and Landscape Board partners, provided a great platform for the researchers to showcase their results, and for the growers to have an opportunity to discuss the results with the researchers.
“These were very successful with most attendees stating that they would be likely to change practices and/or adopt this technology.”
For more information, view the project page, or read the project fact sheet.
Further information:
Tony Randall- Knowledge Broker, SA Drought Hub
0402 245 747, tony@agex.org.au
