Cows need to keep their cool

By Sophie Baldwin

AS THE temperature rises in spring, it’s time for dairy farmers to give some thought to heat stress.

And that’s not just in lactating cows; studies are showing that dry cows are just as important.

A Murray Dairy workshop on the effects of heat stress in dry cows, held in October, delivered some surprising information to the farmers in attendance, giving them some food for thought when it comes to their future management.

Presented by Geoff Dahl from the University of Florida in the United States, the workshop was held by Brendon Martin from Allenby Pastoral Co at Bamawm.

Mr Dahl is involved in the Department of Animal Science in the university’s Institute of Food and Agriculture Sciences, and has been studying the effects of heat stress on cows for years.

He said while most farmers were well aware of the effects of heat stress on the milking herd, dry cows were often forgotten.

“The effects of heat stress on dry cows will have significant impacts on the next lactation and the next generation,” Mr Dahl said.

Studies by the University of Florida have shown heat stress can reduce production in a lactating cow by 5 litres/day and, perhaps even more interestingly, calves born to heat-stressed cows show reduced growth rates and go onto produce less milk as mature cows.

Mr Dahl said all the studies involved similar genetic merit cows, age and feed regimes — the only thing that differed across them was the exposure to heat. The cows were studied in groups of 20.

“The lactating cows were always kept cool and every animal was fed and housed the same — the difference was only ever in the treatment over the six-week dry period. And the more times we did the study the more convincing the data was,” he said.

Heat-stressed cows have a lower feed intake compared to cool cows, and cool cows have an improved immune status.

“Heat stress decreases gestation and results in reduced placental function — on average they calve four days earlier than cool cows,” Mr Dahl said.

The study has also shown immunising cows when they are heat-stressed can reduce the effectiveness of the vaccine.

Mr Dahl said even if cows were heat-stressed for a period of three weeks and then cooled, the effects still carried over into the next lactation, although they were slightly reduced.

The easiest way to tell if a cow is heat-stressed is to observe her respiration rates — anything above 60 breaths for 60 seconds is heat-stressed.

“In general I would say heat stress is experienced across all breeds and we can’t say one breed is better than the other because the effects are always the same,” Mr Dahl said.

He believed preventing heat stress in dry cows was even more important than the milking herd.

“The response on heat-stressed calves is there for life. A heat-stressed calf in utero will never catch up and that is passed down onto their progeny — they always seem to be sitting on the lower limit of normal.

“I would be developing on-farm infrastructure to keep cows cool as my priority. You will always get the most bang for your buck by keeping dry cows cool.”

Mr Dahl said while shade was certainly better than nothing, fans and sprinklers were the way to go. He urged farmers to bring their dry cows up and pop them under the sprinkler at the dairy as well as the milking herd.

Calivil dairy farmer Jade Clymo said the presentation had definitely given him pause for thought when it came to managing his dry cows.

“It certainly is a lot more important than I realised and this has given me a lot to think about when it comes to the future management of my dry cows,” Mr Clymo said.

Brendan Martin said his priority had always been to care for his lactating herd, which was always brought up and put under the sprinklers during hot conditions.

He would love to set up something for his dry herd but he said tough financial conditions were making it difficult to invest in any sort of infrastructure at the moment.