Longevity in cows - how to make it pay

This includes considerations around cow depreciation and longevity, as well as the inconvenience of calving heifers and genetic gain from generation interval.

As David Johnston says, there is a cost of getting a heifer up to being a breeding female and then there is a cost if she drops out, in having to replace her.

Dr Johnston is the principal scientist at Armidale's Animal Genetics and Breeding Unit and a lot of his work is based around traits that drive commercial profitability.

Longevity ultimately boils down to how long a cow lasts in the herd, while also remaining productive.

"As we're facing more dry seasons and higher stocking rates, people will want those genetics that are resilient and more robust to drier times," he said.

However, identifying the cows with the best genes for longevity was difficult, because studs select for a range of traits and the best animals were typically the youngest.

"(Seedstock herds) tend to want to run their best genetics, so we don't get a really good example of the seedstock herds getting longevity because they're getting rid of their older cows to make way for their younger cows," Dr Johnston said.

Elders senior livestock production advisor, Rob Inglis, said the economics of keeping older cows had also changed.

"In terms of commercial value, two years ago you could sell 10-year-old cows with a reared calf, but today I would suggest once they're over six, they're probably fat value," he said.

He said once a cow got past six she also had increased risk of metabolic issues such as grass tetany and hypocalcemia.

"The data tells us ... that the most profitable animals are the ones that calve in the first cycle, in the first three weeks of calving," he said.

In his view, many producers should aim for higher heifer retention. He said producers typically weren't retaining enough heifers and hence herds were tending towards an older average age.

"Higher heifer retention equals a younger herd, which equalled less disease risk and higher genetic gain," he said.

So if producers culled more of their older cows, how could they identify those with the best genetics for longevity?

Dr Johnston said this was something the team at AGBU was looking into and included measuring the component traits, such as calving ease, reproduction, structural and udder soundness.

In northern herds, they were also working with producers on traits such as immune competence and adaptation.

He said in their work they were discovering that retention of fertility in a young female, for instance, was largely independent of performance traits such as fatness, muscling and growth and so a new breeding value was being developed around this.

"That's going to be a new EBV that's going to be released shortly and I think there will be a lot of interest from the commercial industry," Dr Johnston said.

Dr Johnston also explained that the commercial cull value of a cull cow is an important source of income for producers and one not to be underestimated.

"A lot of people will cash out a 10-year-old cow rather than letting her go to 15 when she might not have any value," Dr Johnston said.

"Even the cull cows that don't get in calf are an important source of income. Longevity, per say, is not always the biggest driver of profitability."

Gavin Hulm is a commercial producer at Rannock, with a herd of 100 to 120 Shorthorn breeders.

He can get wet winters, so in his conditions, sound feet and good udders were a key factor as to whether a cow was retained.

"I've got cows that are 10, 11, 12 years old and their udders are still holding on, their feet are still good," he said.

He wasn't keen on "mucking around" with any more heifers than was necessary.

While he recognised that was typically where his best genetics were held, "if you can keep your herd for another year, that means you can sometimes keep a few less heifers to muck around with", he said.

"It's a fine balance between the need to replace those females as a genetic point of view."