WHERE growth and carcase traits have long dominated selection pressure for beef producers looking to increase kilograms per hectare, herd rebuilding has shifted the focus to total profitability and the role fertility plays in that.
Research into the contribution of puberty in heifers to herd reproductive performance has been making solid strides, with imaging technology paving the way for new approaches.
Scientists from the Animal Genetics and Breeding Unit (AGBU) at Armidale and NSW Department of Primary Industries last year conducted a pilot study in two southern Angus herds using ovarian scans to monitor onset of puberty and are now planning a new, large industry-based project.
Speaking at the 2016 Graham Centre Beef Forum in Wagga Wagga last month, senior livestock research officer with NSW DPI, Dr John Wilkins said that the earliest mating of heifers was obviously constrained by puberty, but assessing or measuring age at puberty has previously been difficult.
However, imaging the activity of ovaries using real-time ultrasound scanning can be used to determine the age at puberty (and weight at puberty, if it is collected at the same time), a trait that has been shown to be heritable, he said.
The AGBU’s Dr Rob Banks, commenting on the genetic aspects, said that when using estimated breeding values (EBVs) in selection programs, days to calving was the key one that directly related to herd fertility.
However, this trait had low heritability, meaning that genetic progress will be slower for it, in comparison to growth and carcase traits, he said.
“The potential is that with good direct measures of age at puberty, this would allow breeders to collect data that will contribute to the days to calving EBV, helping to make it more informative,” he said.
“What we are aiming for is a trait with higher heritability and that also relates to lifetime fertility.”
Recent work in northern Bos Indicus herds used routine imaging of ovaries to accurately determine age at puberty in heifers and showed the trait to have greater than 50 per cent heritability.
“We now need a good picture of what is happening with Bos Taurus breeds for the southern industry,” Dr Banks said.
Dr Wilkins said imaging showed the development of follicles on the ovary, with the appearance of a corpus luteum identifying animals that have ovulated.
“Most southern beef producers are now aiming for two-year-old calving,” he said.
“When a heifer has had some cycles previously, they are more likely to mate and conceive earlier, which reduces the chance of missing a year subsequently.
“Even if you are not aiming to mate at a young age, there is evidence from previous research that age at puberty in heifers is genetically related to fertility in adult cows.”
Last year’s pilot project involved a 140 head Angus herd at Trangie and a 400 head commercial operation in Victoria.
Heifers were scanned using imaging three to four times from a liveweight of 250kg up until just prior to mating at 350 to 400kg.
“What it showed was a large difference between herds in the relationships between age and weight with onset of puberty,” Dr Wilkins said.
Dr Banks said the next step would be to collect ovarian imaging information on large numbers of animals from commercial herds of Angus and Hereford.
“We want to accumulate sufficient data to enable us to understand the genetic relationships between age at puberty, body composition and lifetime branding rate,” he said.
Ultimately, the work would enable development of a potential age-at-puberty EBV, and possibly other new EBVs related to fertility, he said.
Depending on the amount of data that can be collected, that is likely to take three to four years.
Measuring puberty in heifers with ultrasound imaging was another tool in the kit to improve herd fertility, the scientists said.
Dr Wilkins estimated an increase of just 1pc in output by improvement in fertility would be worth in the vicinity of $23m to NSW’s beef industry per year, based on Australian Bureau of Statistics data for 2104/15.
“And that is conservative considering current and future projected cattle market prices,” he said.