Dr Tracy Stirling
Dairy Australia Award Winner
Breeding more fertile cows
For many years, dairy farmers have focused on breeding for high milk production. But has success come at a cost?
According to Dr Tracy Stirling from the University of Melbourne, continued breeding for high milk production in dairy cows has led to physiological changes associated with a decline in cow fertility.
“Evidence suggests that pregnancy rates for dairy cows have decreased by around one per cent every year over the last ten years,” said Tracy.
“A one percent change in pregnancy rates in the first 6 weeks of the breeding period is worth $3 per cow in net profit”.
“Therefore selectively breeding for higher IGF-1 levels could be an effective way to breed for improved fertility.”
This equates to over $5 million over the national dairy herd. So it’s important we work to slow—and ideally reverse—this trend.
“It is difficult to breed improved fertility into new generations—it has a low ‘heritability’. It may be more effective to identify other traits that are associated with fertility but have a higher heritability.
“We’ve recently learned that a cow’s level of a particular hormone—insulin-like growth factor-1 (IGF-1)—is associated with both milk production and fertility. And fortunately, it has higher heritability.
Tracy, however, will now be investigating IGF-1 in Holstein bulls rather than cows.
“Because of the use of artificial insemination, most genetic progress in dairy cows on a national basis, comes from the sire,” said Tracy.
“If a bull’s IGF-1 status can be correlated with its breeding values for production and higher fertility, sire selection for IGF-1 would be an efficient way to improve the genetic progress of cow fertility as well as productivity.”
This project has potential to significantly improve productivity of individual dairy cows through breeding selection, and as a result improve industry profitability.