A SIMPLE blood test could be the key to arresting declining dairy cow fertility, according to a University of Melbourne researcher.
Dairy research fellow Tracy Stirling has found poor reproductive performance in cows can be predicted by the concentration of a small, naturally occurring protein in their blood called insulin-like growth factor 1.
Cow fertility, as measured by the six-week in-calf rate, had been declining steadily since 2001 at a rate of about 1 per cent a year, Dr Stirling said.
She said poor cow fertility came at a significant cost to the dairy industry, as it resulted in more inseminations, higher veterinary costs, an increased culling rate and higher replacement costs.
"A 1 per cent change in the six-week in-calf rate is worth at least three dollars per cow in net profit," Dr Stirling said.
"This equates to more than $5 million per year over the national dairy herd."
Dr Stirling said the reproductive performance of a cow was the result of both management and genetics.
However, most of the variation in reproductive performance was due to management at the herd level.
Dr Stirling's research, funded by Dairy Australia, and supported by Genetics Australia and Rivalea Australia, involved more than 100 farm visits and 6000 Holstein cows in Victorian dairy herds.
Blood samples were taken from each cow to measure IGF1 levels, as well as measuring cow size (pin height and hip width), condition-score changes across lactation, and recording production and reproductive performance.
The results of the study showed that placing selection pressure on high milk production had indirectly resulted in cows with a larger stature that lost more body condition in early lactation and were thinner overall.
"These cows have lower milk solids concentrations, and lower IGF1, which was found to be moderately heritable," Dr Stirling said. "They are also likely to have poorer reproductive performance.
"Significant genetic correlations suggested that many of the same genes affect these traits. Similar studies conducted in New Zealand have shown that the NZ Friesian has higher IGF1 than the higher-producing Holstein derived from overseas genetics.
"Cows with high IGF1 are more likely to recommence cycling and ovulating sooner after calving than cows with low IGF1."
Dr Stirling said this was because IGF1 acted directly on the ovary to promote ovulation.
"Not only does IGF1 affect fertility through its direct effect on the ovary, but it is also associated with the way that cows partition energy," she said.
"Cows with low IGF1 are more likely to partition more energy towards milk production, thus leaving less available for things like fertility and body condition.
"It is possible that selecting for high IGF1 could be one way to improve fertility, and this could be done by increasing the accuracy of the ABV (the Australian Breeding Values) for fertility, since IGF1 is heritable."
Further research will focus on measuring IGF1 in bulls, to investigate the potential to improve cow fertility through sire selection for IGF1.
