IMPROVING accuracy in fertility breeding values can reduce cow wastage and accelerate genetic gain, co-lead scientist Dr Chris Burke says.
One way of doing that is to find new traits to improve cow genetic merit for fertility and the most promising is the age of cow puberty.
Fertility makes up 13% of the index weighting in breeding worth (BW) but it also has low heritability.
In recent years the fertility of the national herd, while good by international standards, has not improved when measured by the six-week in-calf rate.
If national targets for reproductive performance were reached $500 million a year more profitability for dairy farmers would be generated.
A major project led by Burke, Dr Susanne Meier and Dr Claire Phyn has run since 2014 using two groups of females with extreme differences in their fertility breeding vales (FBVs).
After widespread contract mating of 2500 cows to selected sires, 640 Holstein-Friesian heifer calves were collected by DairyNZ, half of them with high-FBV (plus 5%) and half with low-FBV (minus 5%) and run as a herd.
Other differences in genetic traits were evened out as much as possible.
In the lead-up to heifer mating in 2016 both groups showed the same rates of live weight gain but the high FBVs reached puberty on average 21 days earlier than the low FBVs, 358 days versus 379. They were also 25kg lighter at puberty, 271kg versus 296kg.
“Puberty differences could provide us with earlier predictors of fertility than the current measures and offer an exciting opportunity to improve fertility in the whole dairy industry,” Burke said.
The puberty trait is more heritable and could therefore improve the reliability or accuracy of the fertility BV for younger bulls.
Puberty and the onset of oestrous can be measured with activity monitors worn by the cattle for the number of steps and times spent standing up and lying down.
He thinks new models of Fit-Bits for cows with different applications in measuring physiology are likely to become more commonplace in dairying.
Measures of cow fertility could effectively start 12 months earlier than the three-week submission pattern in first lactation but culling heifers on the basis of late puberty isn’t very practical, Burke said.
When managed and milked together at AgResearch’s Tokanui dairy farm, the high FBVs went on to have substantially greater three-week and six-week submission rates in first lactation.
After 12 weeks of mating in 2017 18% of the high FBVs were not in calf versus 42% of the low FBVs.
Burke said the large differences in submission and pregnancy rates provide confidence in the current FBVs.
The economics of reproduction mean the measured 34% six-week in-calf rate gap and the 25% not-in-calf rate gap would add up to $166,750 to farm profitability in the average-sized herd of 432 cows.
That is the difference between a herd of plus-5% FBVs and a herd of minus-5% FBVs, neither of which is likely to occur in reality.
However, cows with strong fertility contribute a much tighter pattern of calving across the herd and generally have longer lactations.
As the project continued into the second lactation (2018-19) the big differences in reproductive measures between the two groups continued to show up.
Burke said not all the poor fertility cows were lost out of the system during first lactation as many farmers believed they would be.
Now, at the end of second lactation, there are 177 high FBVs due to calve next season but only 68 low FBVs.
Annual loss rates, not all related to the fertility study, were 30-40% in the low FBVs.
“It emphasises again the link between reproductive performance and cow wastage,” he said.
The project continues with plans for more than 5000 heifers from 60 participating herds to be tracked later this year.
Burke said puberty will be measured to ensure it was indeed correlated with subsequent cow fertility, across different breeds and farm environments.
“We want to see that puberty is indeed a good indicator of cow fertility and that it is not causing a disadvantage in other traits.
“We need to follow all these animals through at least the first lactation to ensure we are getting the gains we are aiming for.”
Benefits in genetic gain for farmers from the project are probably five to 10 years away if everything goes right.
“This trial is readily relatable for farmers.
“Reproductive performance is among their top 10 concerns and they do not like to see cows sent to the works because of failure to get pregnant.
“We have provided hope for the future in reproductive performance.”
But Burke also sounded a note of caution.
“Most of the influences over reproduction are in farmers’ own hands – so we don’t want to have them overly confident that all their problems will be solved genetically.”
The cow fertility project is a major component of the Pillars of a New Dairy System, a seven-year partnership between the Government and the dairy industry that addresses an estimated $1 billion a year of inefficiencies.
Funding is from DairyNZ and the Ministry of Business, Innovation and Employment with support from AgResearch. More funding and resources are provided by Fonterra, LIC and CRV Ambreed.
