Managing Heat Stress in Sheep Project Update

Over the past six months, 3 UNFS sheep producers were involved in a project to ‘Manage Heat Stress in Sheep’, run through the University of Adelaide’s Davies Livestock Research Centre. The focus of the research is to increase conception rates and mitigate the impacts of heat stress on ewes and rams.

The project administered two treatments on farm:

  1. delivery of a single pre-joining drench of ADE in ewes at joining
  2. implant of melatonin in ewes and/or rams one month prior to joining

The reasons why the research team believe these interventions will improve the fertility of ewes joined during summer are summarized below. 

Potential Benefits of Regulin

Melatonin, the main component of Regulin® implants, improves the fertility of ewes and rams when they are bred out of season. Melatonin is also a strong antioxidant, with the potential to reduce body temperature, and, therefore, should alleviate the impacts of heat stress on ewe and ram reproduction. Therefore, we believe that raising melatonin levels of ewes and ewe lambs during joining and the first 2/3 of pregnancy will improve conception rates, twinning rates, improve fetal development and general ewe wellbeing. The overall result being an improvement in the fertility and fecundity of flocks which join over summer.

Potential Benefits of Vitamin supplementation

Loss of embryos within 17 days of joining is responsible for roughly 20% of potential lamb loss within South Australian Merino Sheep flocks. One likely cause of embryo loss is high ambient temperatures, which increase uterine temperature and damage the embryo. An effective way to reduce heat induced oxidative stress is to provide ewe with high levels of vitamins A, D and E. Vitamin E increases the ability of ewes to cope with heat stress, Vitamin A and D are crucial for correct embryo development and are likely to protect the developing embryo from the damaging effects of heat stress. Therefore, we believe that providing ewes with an oral drench containing high levels of Vitamin A, D and E at the start of joining will reduce embryo loss in ewes joined during summer and thus, increase flock fertility and fecundity. 

Climate Information

Alongside of the supplementation strategies described above, technologies to measure climate within joining paddocks were deployed, and software will be used to map paddocks and look at how all of these features interact and affect conception rates/ joining outcomes. The ultimate aim is to understand how the severity of heat events affect sheep from different agro-ecological zones, and to develop climate calculators that can determine whether alterations in management (i.e delivery of a supplement or slight change in joining time) could improve flock fertility.

Preliminary Results

On-farm data from approximately 7,700 breeding ewes across 17 sheep flocks and 13 producer sites have currently been collated. A total of 14 flocks used melatonin implants and 15 flocks used ADE drench, with one flock using both melatonin and ADE in a subset of ewes. Initial, preliminary analysis of these results indicate that both ADE and melatonin reduce the number of dry ewes at scanning, increase the number of ewes carrying multiple fetuses and in turn increase the number of lambs (fetuses) scanned per ewe joined (Table 1).

Table 1: Overall results from 17 sheep flocks across 13 producer sites

%Dry%Single%MultipleFetuses/ ewe joinedFetuses/ ewe pregnant
*Only One Farm

There were four producer sites that fell in the Upper North: 2 using only melatonin; 1 using only the ADE drench; and one using either melatonin or ADE. Table 2 reports on the results from these sites. All sites using melatonin showed a higher number or fetuses/ewes joined compared to control flocks.  Only one of the two ADE flocks showed an increase in the number of fetuses/ewes joined.

Table 2: Results from 4 producer sites in the Upper North

Producer SiteTreatmentNumber of Ewes%Dry%Multiplesfetuses/ ewe joined

Overall, the results of this study indicate that supplementing ewes with a single dose of ADE at joining increased the number of fetuses/ewe joined by 3-9%. Similarly, supplementing ewes with a single melatonin implant at joining increased the number of fetuses/ewe joined by between 7% and 28%.

Associate Professor Will Van Wettere will be presenting Upper North results at our upcoming “Improving Weaner Management Workshops” at Wirrabara and Wilmington in June.

1st June 2023 Rachel Trengove