After a year of analysing figures of mating and subsequent calving dates from the New Zealand Animal Evaluation (NZAEL) database the worth of high fertility bulls has been proven.
“From some of the other research we’ve been doing I had expected high-fertility bulls would have this effect but I didn’t think it would get so many people excited,” one of the researchers, Peter Amer from Dunedin-based AbacusBio, said.
About 4.5 million cows and 10 million mating and calving records were looked at with AbacusBio scientist Hadyn Craig crunching the numbers.
“We looked at the number of cows which had calved by day 42 after the planned start of calving as a fertility marker,” Craig said.
“That is six weeks which is two cycles for a cow and most farmers AI for six weeks so it seemed a logical date.”
Although high-fertility bulls hardly increased the day-42 calving rate when used over high-fertility herds, in low-fertility herds the results astounded researchers.
“It shows that if you have a low-fertility herd then you can make a difference by using genetics,” Craig said.
“Management is a key aspect of fertility, such as having cows at the right condition score at calving and mating, making sure there are no underlying health issues, but this research shows that bull selection also has a huge impact.
“For farmers with low-fertility herds, they should use bulls with a high-fertility breeding value that are also still strong for other traits such as production. For those with high-fertility herds, just choose the highest BW bull,” he said.
“A high-fertility bull won’t give you better fertility if you already have a high-fertility herd. Once you have high fertility you really can’t make it a lot better.
“However, good fertility genetics, which most high BW bulls have, keeps a level of protection against potential future fertility problems due to some uncontrollable factor.”
The researchers said the benefit of using high fertility bulls in a low fertility herd would take three to 10 years to take effect as it was the daughters of the high fertility bulls that made the difference – not the first mating using a high fertility bull.
“It’s nothing to do with the semen of the bull or how it affects conception or the pregnancy or anything like that. We are talking about the genetics of the daughters and grand-daughters from the high-fertility bulls,” Amer said.
Although high-fertility bulls could have a lower BW than normal bulls the trade-off would be worth it for farmers who had herds with poor fertility and were battling low days in milk and increased management costs.
The research also showed the South Island had higher fertility on average than the North Island, with every region in the South Island better than the regions in the North Island.
“Also our highest-producing herds, after accounting for breed mix, tend to have better fertility on average than herds where per-cow production is lower than average,” Amer said.
“This is the opposite of what you find in other dairy systems throughout the world. In very high production herds in intensive systems overseas, there tends to be greater problems with fertility.”
He said the research also supported the integrity of the NZAEL database figures and breeding values.
“We only have mating and calving dates but even from these we could still see the difference high fertility bulls made.”
NZAEL developer Melissa Stephen said funding such research was a long-term game.
“In the current financial situation, it is critical to recognise the value of investing in genetics. The costs associated with AI are repaid many times by the increased profitability of the resulting heifer replacements,” she said.
Amer said a dip in the national herd’s fertility could happen because of the low payout.
“We expect to see a dip in fertility because we suspect cows won’t be fed the same. There could be body condition score problems with more farmers having to winter on and unable to afford to feed supplements.
“But now we know, through this research, we can breed cows which are genetically easier to get back in-calf which is important as management interventions can be costly,” Stephen said.
“Where it will go from there will be interesting,” Amer said. “We might see genetic companies offering teams of high-fertility bulls that farmers can use.”
