Disease prevention starts with genetic selection

The HealthyCow index was added to the dairy producer’s genetic toolbox almost three years ago. New evidence shows that those using it are seeing significant reductions in mastitis and lameness alongside improved fertility and longer lifespans.

Disease prevention is the most effective approach to maintaining herd health, and the ultimate place to start is before conception. Getting the genetics right has a profound impact on the ease of managing health but comes with the bonus of improving cow welfare, cutting carbon footprint, saving labour and costs, and boosting a herd’s bottom line.

But with a plethora of genetic indexes now available to dairy producers, it can be difficult to know which to prioritise, and how they relate in importance to other commercial traits.

This is why we introduced HealthyCow (HC) in 2021, which was the first time UK farmers had a single genetic figure to represent overall health. This provided an at-a-glance indicator of which bulls were predicted to transmit the best overall health to their daughters.

HC does this by pulling a range of different health or health-related traits into one figure. These include the three major causes of culling – mastitis, lameness and fertility – alongside others, including calf survival, calving ease and lifespan.

The percentage weightings of traits within HC:

• Fertility 29%
• Lifespan (cow) 14%
• Calf survival 14%
• SCC 13%
• Lameness 11%
• Mastitis 10%
• Functional type 6%
• Calving ease 3%

Now, over two years since its introduction, it is possible to assess the impact HC is having on actual performance.

We have analysed the actual phenotype (or performance) of the national dairy herd, in terms of mastitis, lameness and fertility, and related this to the sires’ HC index. We did this by using data from farm management software and milk recording for each animal’s first to fifth lactations and looked at the sires of these cows.

Some strong trends have emerged through this assessment, not least in mastitis.

When the top 25% (Q1) HC bulls were compared with the bottom 25% (Q4) bulls, there was as much as a doubling in their daughters’ mastitis incidence.

Third calvers by the best (Q1) sires had a 12.2% incidence, compared with 24.9% in daughters of Q4 bulls. A similar relationship is shown through all age groups.

Lameness shows a similar pattern, again demonstrated well in third-lactation cows.

Daughters of Q1 sires were recorded with an 11.4% incidence of lameness compared with those by Q4 bulls recording 15.4%.

This becomes more pronounced through the age range, with fifth calver daughters of Q1 bulls at 13.3% compared with 19.2% for the same age group sired by the lowest quartile sires.

For fertility, the trend is in the same direction, seen clearly through the calving interval of the best and worst HC sires’ daughters.

In every age group, the difference between Q1 and Q4 daughters is 11 or 12 days, demonstrated, for example, in third calvers which come through at 391 days for those sired by Q1 bulls compared with 403 days for daughters of Q4 bulls.

It’s no surprise that with better genetics for mastitis, lameness and fertility, come longer lifespans, and daughters of Q1 bulls were found to live, on average, an extra half lactation longer than those by Q4 HC bulls.

Marco Winters, AHDB’s head of animal genetics, says:

“It’s worth producers remembering that these benefits come pretty much free of charge, and while they may not represent a substantial difference in fertility or disease incidence in one animal, the improvements are massive if they exist across a whole herd.

''And as with all genetic gain, it always comes as a permanent benefit and will pass down the generations to accumulate more.

“Cattle which come with an inbuilt resistance to disease can have a substantial impact on ease of management, labour requirement and the use of antibiotics, amongst a wealth of knock-on benefits.

“These range from reduced milk waste and carbon footprint to improved cow welfare, consumer perception and of course, the bottom line.”

So, how should HC be used alongside other parameters, importantly the Profitable Lifetime Index (£PLI) which has long been recommended as the national breeding goal?

Marco said £PLI should remain the priority for selection on a typical, year-round calving UK farm, with the comparable seasonal indexes usually preferred for spring or autumn block calving herds:

“Once bulls are shortlisted on the relevant profitability index, Healthy Cow is a good option for secondary selection, and will give an indication of which will breed the most health and fertility into their daughters.”

However, the formulae for HC and £PLI include many of the same traits, which means that by breeding for £PLI, improvements are already being made in the health and fertility traits. Marco said:

“In fact, if the traits in £PLI are correlated with those in HealthyCow, it can be seen that for many of them, choosing either index will give a similar result.

“However, the notable exceptions are the production traits which are absent from the formula of HC, which is why we recommend, when it comes to sire selection, that £PLI is the best way of breeding profitability into a herd.

“HealthyCow should generally be a secondary consideration, although the exception should be when a herd has a specific problem which needs to be addressed, in which case, that particular index – say fertility or cell count – may be a better secondary choice.”

HC combines a range of different health or health-related traits into one genetic selection index. It is expressed in £ and represents the financial saving each bull is predicted to pass to his daughters through their better fertility and health.

For example, if a bull has an HC of £400, the better health he’ll transmit is worth, on average, £400 to each of his daughters over their lifetimes, compared with a bull whose HC is zero.