Trevor Parrish, Illawambra Holsteins, Kangaroo Valley, said you wouldn’t pick an animal's ability to handle hot weather by just looking at them which makes an ABV for heat tolerance all the more important if you want to make progress.

Helping our dairy cows tolerate summer heat

Dairy farmers familiar with the impact of hot, humid weather on their herds can now add breeding to their toolbox of ways to help cows handle the heat. 

DataGene’s December release of Australian Breeding Values (ABVs) included the world-first heat tolerance ABV.

DataGene CEO, Dr Matt Shaffer, said while environment and management had a big impact on a cow’s response to the heat, genetics also played a role.

“The heat tolerance ABV allows farmers to identify animals with greater ability to tolerate hot weather with less impact on production.”  

Fourth-generation dairy farmer and seed stock producer, Trevor Parrish, Illawambra Holsteins, Kangaroo Valley, said the heat tolerance ABV would help him breed what clients wanted. 

“We sell up to 100 females and 30 bulls a year to dairy producers in NSW and interstate,” he said.

“If bull clients are asking about an ABV then I need to make sure we can provide bulls that meet their requirements and the new heat tolerance ABV is no different.”

The Illawambra herd ranked number one in Australian Holstein herds for profit health weighted index and type weighted index and number two for balanced performance index (BPI), in DataGene’s December ABVs.

Milking up to 240 cows all year round, Mr Parrish said while their farm had plenty of paddock shade and at the dairy, production and fertility were affected by hot, humid conditions.

His experience has shown that cows which have positive heat tolerance ABVs are not necessarily light coloured. Some females with the highest heat tolerance ABVs have predominantly black coats.

“You wouldn’t pick their ability to handle hot weather by just looking at them which makes an ABV for heat tolerance all the more important.”

In hot, humid weather cows eat less and spend more energy trying to regulate their body temperature. This can lead to a drop in milk production and quality and reduced in-calf rates.

With a reliability of 38 per cent, heat tolerance is favourably linked with fertility and unfavourably with production. So a strong focus on heat-tolerance bulls may improve fertility but compromise production.

Mr Parrish has been genomically testing all Illawambra heifers for two to three generations, allowing him to cull on BPI.

“We focus on the whole herd rather than individual cows and draw a line in the sand for BPI at 150. We need to ensure we identify animals with heat tolerance which don’t sacrifice production.”