As temperatures increase worldwide, heat stress is becoming a global issue. A new study may help dairy producers to breed cattle that are more resilient to heat waves.
Heat stress is a condition that arises when an animal is no longer able to adequately regulate its body temperature – it overheats. Heat stress also makes animals more susceptible to diseases and is a key cause of production losses in farm animals in tropical countries that experience hot temperatures year-round.
A recent study in Tanzania1 found that milk production in dairy cows dropped by 0.5 litres for every unit increase of temperature.
Dr Bonnie Mallard, a professor in the Department of Pathobiology at the University of Guelph in Canada, and PhD student Shannon Cartwright, created High Immune Response (HIR) technology to determine cows with high, average, or low immune responses.
Cartwright, while working at the Ontario Dairy Research Centre, used Mallard’s HIR technology to test for cows for a high immune response. Researchers also subjected the cows to higher temperatures, initially to determine changes in function of immune cells in the blood under adverse conditions.
They discovered that cows with a high immune response also had a higher tolerance for increased temperatures. These cows were found to have more molecules that help with vasodilation of the skin, the widening of blood vessels to cool the body, and increased cell proliferation, when exposed to heat.
“These high immune responders seem to have better cooling mechanisms,” explains Cartwright. “Cows that have been identified as high immune responders also have a greater production of molecules that protect cells during heat stress,” Cartwright states. “Heat stress leads to an increase in body temperature that can result in cell death, but cows that produce higher concentrations of protectant molecules can better resist cell death.”
Climate change is an ongoing issue that likely will not be resolved anytime soon, making it important to identify animals that are resilient to heat stress. Selectively breeding cows more resilient to heat stress can make for a more heat resilient herd.
1 Ekine-Dzivenua, C.C., et al. (2020) Evaluating the impact of heat stress as measured by temperature-humidity index (THI) on test-day milk yield of small holder dairy cattle in a sub-Sahara African climate. Livestock Science, 242, 2020, 104314. doi: 10.1016/j.livsci.2020.104314