Heat stress: Managing high temperatures on livestock farms

January and February were particularly warm months across the interior of South Africa this year, raising concerns that the high temperatures could negatively impact conception rates in beef herds and sheep flocks with breeding seasons running from December to March.

- By Dr Johan van Rooyen, Steynsburg Animal Hospital

During our annual pregnancy examinations, data analysis revealed a clear pattern suggesting that bulls, and possibly cows, were less active during heatwaves and/or that some conceptions may have been lost due to heat stress. Most cows were successfully mated either before or after the intense heat period from mid-January to mid-February.

In sheep, we observed that many ewe flocks experienced a delay in the start of mating. This aligns with findings from ram genital soundness examinations, where some rams showed signs of heat-related issues. Rams with higher body condition scores and longer wool were more prone to poor semen quality. It is important to note that the optimal temperature of the testes for semen production is a few degrees below the animal’s body temperature (approximately 39°C). When daytime temperatures exceed 40°C, fertility is likely to be negatively affected. This issue is compounded by heat radiating from bare ground surfaces.

In semiarid regions, rams often show lower conception rates during the summer months. While heat discomfort and reduced activity likely play a major role, other factors may also contribute. Interestingly, experienced producers report that moving mating flocks into cooler mountain areas during summer noticeably improves lambing percentages.

Physical damage to feet

In many parts of the dry western regions of the country, large areas of bare soil and exposed rock lack plant cover and can become extremely hot. We observed a group of weaner and yearling beef cattle heifers that developed lameness due to the intense heat of the soil and rocky surfaces in their camp. More than 30% of the animals were so severely affected that they could not walk to the water points and became dehydrated. Once moved to a shaded river camp with access to water, the heifers recovered completely within a week.