Farmer News
31 January, 2025
Heat tolerance, part of breeding an efficient animal
SEVEN years ago Trevor Parrish’s bull-buying clients were asking about the new Heat Tolerance Australian Breeding Value (ABV).
Now it doesn’t rate a mention, unless it is hot.
But that’s not because the bull-breeder’s clients don’t care about heat tolerance.
It’s quite the contrary. These farmers, who are mostly in New South Wales and Queensland, consider heat tolerance one of the core breeding values that make-up a sustainable and efficient animal.
These farmers, who milk up to 2000 cows, expect high Balanced Performance Index (BPI) bulls to have an above average Heat Tolerance ABV.
“Clients, they are thinking longer term, we have to select for it,” the Kangaroo Valley farmer said.
“Into the future, they are going to want more of a compact cow, a cow that can handle just about everything.
“A smaller cow, with good feet that can walk more and convert feed into milk. A cow that’s efficient.”
Heat tolerance is part of that efficiency.
“Breeders are trying to cover all the bases and heat tolerance (now it has an ABV) is part of a solid, good quality cow,” Trevor said.
DataGene’s Good Bulls Guide reflects the growing focus on breeding heat tolerant bulls.
In DataGene’s August 2024 ABV release, one third (197) of the Holstein Good Bulls had a Heat Tolerance ABV of 100 or more – which is the Australian average.
Included in this group were 34 Holsteins which scored at least 105 for heat tolerance; this means they are five per cent more tolerant to hot and/or humid conditions than the average.
Or the fall in production due to these conditions would be five per cent less than average.
This compares to a small number of bulls that ranked more than 100 for Heat Tolerance back in December 2016, when the breeding value was first released.
Australia was the first country in the world to have a Heat Tolerance Australian Breeding Value.
Scientists developed this ABV by identifying genetic markers for heat tolerance using genomic technology (DNA testing).
Mr Parrish said breeding was one of several tools he used to help their herd of up to 300 milking registered Holsteins handle the humid conditions.
“It is just one of those things, we put sprinklers on to try and ease the heat and we have shade (trees); you have got to have shade.
“Breeding for heat tolerance is just like planting a tree, how long will it be until the tree provides you with shade?
“But if you don’t start planting trees and looking to breed for heat tolerance, it is only going to get worse; it is about starting.”
Trevor, his wife Leah, their daughter Toni and son-in-law Nathan are all part of the dairy business called Illawambra Family Trust.
Nathan and Toni have a rural contracting and fencing business that has been incorporated into the farm business.
They are taking over the running of the farm, while Trevor is more of the herd manager.
There are four other full-time employees and two part-time.
The business also sells about 60 bulls and 100 females annually to dairy farmers and supplies sires to be tested for artificial insemination (AI).
Breeding for AI also requires a focus on heat tolerance for the domestic and international market, according to Trevor.
“A bull that’s above 100 for heat tolerance is a fairly good selling point and you will get royalties on those bulls,” he said.
Most of his herd has a Heat Tolerance ABV of more than 96 which means the cows susceptible to heat “naturally culled themselves”.
“What we used to see here is, in the summer cows could be in calf and three months later they come in bulling because they have aborted their calf due to the heat,” he said.
“So, because of their fertility they end up in-calf later or they don’t get in calf which means they are culled.”
The science behind the Heat Tolerance ABV has provided him with reassurance when it comes to making breeding decisions.
“The good thing with heat tolerance is there’s no human error,” Trevor said.
“The reliability is at 48 per cent and yes, I would like it higher, but that is all a DNA test.
“A bull at 105 is better than 95, it is that simple.”
Trevor’s herd is medium-stature and fed a pasture/ TMR diet from about 70 ha plus about two tonnes/cow/ lactation in the bale of a pellet supplied from a nearby ethanol plant.
More than half the herd are heifers as Trevor has opted to retain his best genetics.
Anything that’s not over 330 BPI may get a dose of Angus semen and all animals below 350 BPI are for sale.
“I think AI centres won’t take bulls that aren’t good for heat tolerance. It will be like calving ease – now they won’t buy a bull that causes difficult calvings.”
To breed for improved heat tolerance, Trevor suggests farmers look for high BPI bulls with a Heat Tolerance ABV of more than 100.
DataGene recommends using a team of bulls to allow for the lower reliability of the Heat Tolerance ABV.