AHDB announces three changes to dairy genetic evaluations

AHDB Dairy will introduce three changes to genetic evaluations when dairy bull proofs are published next week (6 April).

The major revision is the launch of HealthyCow (HC), which rolls all individual health traits into one figure.

Alongside this, a gestation length (GL) index will be introduced as a breeding tool that can be used to assist with management, while a new rolling base will ensure genetic evaluations are as accurate and up to date as possible.

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HealthyCow

HealthyCow wraps up 10 health or health-related traits into one figure. It has been designed to help producers identify, at a glance, the bulls that pass better overall health on to their daughters (see “Genetic traits within HealthyCow”).

These traits have been used individually by breeders for many years, but have now been amalgamated.

It is expressed in pounds and represents the financial saving each bull is predicted to pass to his daughters through their better health.

For example, if a bull has an HC of £300, the better health he will transmit is worth, on average, £300 to each of his daughters over their lifetimes, compared with a bull whose HC is £0.

Marco Winters, head of animal genetics for AHDB Dairy, says farmers who want to improve a specific trait should still focus on this.  

However, HealthyCow will give them a quick impression of whether a bull is an overall health improver.

“Each of the traits within HC remains in the profitable lifetime index [PLI], which itself also includes milk production and efficiency,” he says.

“Our advice remains that year-round-calving producers should base their primary sire selection on PLI, but the many for whom health is a rising priority may find a single genetic value for health a useful secondary guide.”

Gestation length

The second change is the introduction of a GL index, providing a prediction of gestation length for the bull’s calves.

Expressed in days as a deviation from the national average, a bull is likely to have a figure ranging from about -5 to +5 days, where zero is the average and positive figures represent longer gestations.

This will be a standalone figure and not included in PLI.

“For those with tight block-calving periods, it can be used as a management tool when shorter gestations can help bring calvings from later inseminations back on track.”

Rolling base

The final change is a move to an annual recalculation of each breed’s average for every trait.

Mr Winters explains: “Since genetic indexes have been in use, they have always been expressed against an average animal, with each trait’s average set at zero.

“But, as the national herd makes genetic progress, the average also rises and for this reason, is periodically reset to zero. Without the reset, as genetics improve, almost every animal would eventually be better than the ‘average’,” he says.

Until now, this reset – or base change – has been carried out every five years, but this will now move to a rolling base, which means the average against which all animals are compared will be recalculated every year.

“This has become more important in the face of rapid genetic progress brought about by the use of genomics,” says Mr Winters.

It means there won’t be a big drop in figures every five years, but a small change each year, and bulls will remain in the same position in the rankings.