Ivan Holloway, the production animal business manager at VetLife Timaru, says there are stark differences in the way heat affects cows compared with sheep, but most issues are manageable with careful planning.
With cows, predominantly dairy, heat stress has been highlighted through technology in recent years, Holloway said.
“What we’ve been seeing with the advent of technology is a lot more wearables on cows, things like cow collars, measuring rumination rate and that sort of thing, and a lot of farmers last year were getting heat alerts,” he said.
“So if temperatures are going to increase and become more extreme then we are going to have to keep an eye on things.”
Holloway said this is concerning in some areas of Canterbury, where dairy farms are reliant on centre pivot irrigators at the expense of trees, which would normally provide shade for stock.
“One of the things you do with heat stress is seek shade, but there isn’t any shade in these areas.
“And with the cow you’ve got to remember with the rumen it’s a fermentation chamber and they actually create heat and they can’t dissipate it when the temperatures are getting higher and higher, when they would normally seek shade.”
With limited options for shade on some dairy farms, Holloway said, “we need to be thinking about different ways we can mitigate this”.
“In a crowd you get 600-700 cows all together in the middle of milking. They all generate heat and while in close proximity generate more and more heat.
“In America they run shower lines under the pivots and that sort of thing so the cows can be damp. So maybe in cow sheds we could be thinking about shower lines in there,” Holloway said.
He said the No 1 thing is having plenty of drinking water available for stock.
Sheep, on the other hand, tend to do well if it’s dry – as long as they have access to plenty of water and feed – because the heat often fries parasites.
“The worm burdens are not as bad throughout the warm periods,” said Holloway.
However, even though “they are often sitting redundant in dung pats, as eggs or inhibited, they’re still there building up in numbers, probably because they are still breeding in the animals so the eggs are still being put out”.
This is why, among other reasons, it is important for farmers to keep an eye out for rain after extended dry periods.
“If and when it does rain, and you have a low pasture cover, you get a film of water across, which makes the dung pats break down and spread larvae,” he said.
“And of course with that lower cover, the majority of the parasites live in the first 1-2cm, and with only 1cm or 2cm there the animals are ingesting the larvae in great numbers.
“So with the parasite breakdowns during rain following a dry spell we often see people get caught out, so watching for that rain and acting accordingly is essential.”
Holloway said in combination with an increase in parasites, for some regions that are prone to things like facial eczema, rain following a dry period can create the perfect storm.
As well as this, one of the most prevalent issues in NZ over the summer months is flystrike, with 2-10% of the national flock being affected every year.
“Watching out for flystrike is important, as when it’s hot and humid, flies, particularly the Australian green blowfly, will have a ball,” Holloway said.
This can be prevented and managed through dagging and crutching, and the application of preventative chemicals using well-functioning gear and following instructions carefully.