Overheated herds

This year’s higher than average summer temperatures have highlighted a growing animal welfare issue for the US livestock industry, and it is one that will prove equally relevant for Australia’s farmers as we head into warmer weather. Cattle prefer a cool climate, and suffer heat stress when they become too hot. If symptoms of the animals’ discomfort go unrecognised, a dairy cow’s milk production and fertility can be affected, while the result for intensively farmed beef cattle may be growth and weight loss, which leads to reduced meat production.

As some of the physiological responses to excessive heat are experienced internally by cows, and therefore less likely to be noticed until the animals are severely affected, livestock researchers from the University of Arizona, led by dairy specialist Robert Collier, have developed a vaginal sensor that can measure a cow’s core body temperature, and a leg sensor able to determine whether the cow had been sitting or standing.

It is thought cows remain standing for longer periods when their body temperature rises higher than 39 degrees celsius because having more of their bodies exposed to the air helps to cool them down. However standing uses more energy which exacerbates their heat stress.

“Heat exhaustion is a common problem in summer months over most of the US, especially as our cows have gotten to be high-producing animals. They’re eating more and producing more heat, so they’re more sensitive,” Collier said.

Because cows are panting animals their respiratory rates can go from a standard 35-50 breaths per minute, to 120-140 when they are heat stressed, and when they pant that much they become less inclined to eat, which reduces their milk. Cows that experience heat stress also tend not to conceive so easily and with no new calf on the way, milk production problems arise as with no calf cows “basically dry up.”

In addition to providing shaded areas and sufficient drinking water, Collier said cows should also be encouraged to lie down, and be misted regularly with cool water so the effects of heat stress are minimised.

Anne Layton-Bennett