The genetics of dairy-cow fertility has undergone a transformation since the early 2000s. Geneticist Marco Winters predicts the UK herd will return to fertility levels seen during the 1990s before the end of the decade.
TEXT ANN HARDY
Around five years ago, Marco Winters, AHDB’s head of animal genetics, predicted that the average UK calving index across the national dairy herd would hit 390 days by the end of 2024. That was at a time when calving index was more than 400 days.
And, with 2023’s figure projected to be around 393 days, he can confidently say this prediction is on track. Today he is projecting further ahead, and says the UK will reach an average calving index of 385 days before the end of the decade.
He bases his prediction on genetic trends for fertility, which have been transformed during the past 15 years (see Figure 1).
For this, he praises Holstein breeders, who have embraced the female fertility index (FI) and used it in their genetic selections since the index was launched in 2005. He is also fulsome in his praise for the Holstein breed, which has responded so well to genetic selection.
But the picture was not so rosy before FI was launched. Today’s improvements follow years of decline when producers had little idea of any bull’s ability to transmit female fertility, and were largely selecting for milk production. This had the effect of not simply ignoring cow fertility, but of positively selecting against it. This was driven by the moderate negative correlation between milk production and fertility which was known at the time, but was difficult to address.
Genetic indexing
However, today’s sophisticated computing power and genetic indexing system have turned this situation on its head.
“It’s allowed for the development of more holistic indexes, such as profitable lifetime index (£PLI), which includes an element of fertility alongside other traits,” says Mr Winters.
“By using £PLI and other modern selection indexes, it’s been easy for producers to include fertility in their genetic selection criteria, without compromising other important traits.”
With his earlier prediction still on target, Mr Winters feels confident in predicting more improvement ahead.
“This improvement will be slower, as we’ve taken the low-hanging fruit, but we expect to continue to cut calving interval by about one day every year over the next five years.”
This puts the national dairy herd on target for a calving interval of 385 days by 2029. “This will bring us back to the fertility levels of the mid-1990s,” he says. “But impressively, it has been achieved at the same time as milk yields have significantly increased.”
Rich rewards
Breeding for fertility has been a top priority for Cheshire-based producer Andy Rutter for more than 20 years, and has reaped rich rewards for his 390-cow herd. This includes increasing pregnancy rate to an impressive 33% (12-month rolling average), reducing age at first calving to 23.5 months, and cutting calving index to 370 days. All this has been achieved while milk production has risen to around 10,000 litres, at 4.4% fat and 3.4% protein, for the all-year-round-calving herd.
Milk sold per cow per year is the KPI that Mr Rutter says keeps the dairy in business. “And there’s nothing that drives milk production like fertility and having ‘fresh’ cows,” he says.
He applied this philosophy to his former role at Genus ABS, where he worked for 18 years, before he returned to run his family’s tenanted farm in 2018. He recalls that as soon as fertility index (FI) was introduced by AHDB in 2005 it became a major selection trait for the sires he used on his herd, second only to the more holistic Profitable Lifetime Index (£PLI).
“I spent a lot of time promoting double-digit FI bulls and was so pleased to see the national decline in fertility gradually start to improve,” he says.
Mr Rutter believes there was a nervousness among producers to select high FI in the early days because fertility was perceived as a low-heritability trait.
“But low heritability doesn’t necessarily mean there’s a lack of genetic variation from which to select, or that good genetic progress for the trait can’t be made,” he says.
He says the early reluctance to use FI was compounded by the knowledge that fertility and milk production were ‘antagonistic’ traits. “And then along came ‘curve benders’, like Oman, who were able to deliver both.”
Now he says it’s possible to ‘have your cake and eat it’, with a plethora of high-fertility and high-production sires now available. “It’s fantastic to see what the Holstein breed has achieved, and how the vast majority of commercial producers did buy into this trait and have lifted the fertility of the national herd,” he says.
It has also helped his herd to achieve its impressive gains. Mr Rutter uses the AHDB Herd Genetic Report that ranks cows for many genetic traits, including FI, and tracks their genetic progress. “Our milking herd now runs at +2.3 FI, while the youngstock are at +5.1,” he says. “We’ve worked out that each FI point cuts about two days off our calving interval, which is far better than the theory predicts.”
Figure 1: Actual and estimated calving interval by year of calving
Culling data
This is also reflected in culling data that shows that barren cows, which were the number-one reason for culling in 2018, are now down to third or fourth place. High-reproductive performance is also the result of the herd’s RMS and vet teams, and Mr Rutter says strict protocols exist for problem and difficult-calving cows. Today, gains made in health and fertility have allowed selection criteria to be broadened and he has turned his attention to measures of efficiency.
“£PLI has always been the mainstay of our selection as it’s an extremely balanced index. It does a lot of the legwork for us and then I look at how I can tweak it to get what I want, including kilogrammes of fat and protein, rather than percentages, to meet our business’ Müller liquid contract.
“And we are now bringing EnviroCow into play to improve our feed efficiency, as well as our carbon footprint,” he adds.
To sign up for a Herd Genetic Report, visit: https://ahdb. org.uk/herd-genetic-report-sign-up.
What is fertility index?
Fertility index provides a prediction of female fertility. A bull with an above-average fertility index (FI) will breed cows with improved calving intervals and better non-return rates. As a guide, every point increase in FI will decrease calving interval by 0.6 of a day and improve non-return rates by 0.25%.
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