A new mastitis genetic evaluation will be published by AHDB Dairy to coincide with the issue of next month’s bull proofs (4 April) for the dairy cattle breeds. The new evaluation gives an indication of a bull’s ability to transmit mastitis resistance on to his daughters and is expressed as a percentage on a scale of about -5 to +5.
As with the Somatic Cell Count PTA (Predicted Transmitting Abilitiy) – which has been used successfully by milk producers to breed lower cell counts into dairy cattle for many years – negative figures are desirable for mastitis.
This means that for every one percent decrease in a bull’s Mastitis PTA there will be a corresponding one percent decrease in the proportion of his daughters expected to get mastitis.
Marco Winters, head of animal genetics for AHDB Dairy explains: “The degree to which any animal can be improved through breeding depends on the heritability of the trait being improved – in other words, the degree to which it passes from one generation to the next – and how reliably we are measuring that trait.
“In the case of the new mastitis evaluations, we have used extensive national records from all of the UK’s milk recording organisations to assess the degree to which each bull’s daughters are able to resist mastitis, and from that information, we have established every bull’s breeding pattern.”
Using this information it has been established that the heritability of mastitis is about four per cent. This is on a par with several traits being improved through breeding and it is higher than some which are making good genetic progress, including female fertility.
“This means we are confident dairy producers can improve the mastitis rates in their herds through breeding which – although a slow and long-term process – reaps rich rewards over the generations,” he says.
The existing SCC PTA will continue to be published alongside the new mastitis evaluation since – although they are similar – the two traits are not identical.
“The majority of bulls which reduce their daughters’ cell counts will also reduce mastitis,” says Mr Winters. “This is seen in a correlation between the two evaluations of +0.8, indicating there’s a strong, but not exact, likeness between the two traits.
“However, there are a few bulls which will reduce one and not the other trait, and this new information will help pinpoint those bulls,” he continues. “It means farmers can consider both traits and they can make their breeding decisions with this extra knowledge and according to their herds’ precise needs.
“As with all individual trait PTAs, the Mastitis PTA should be used as part of a broader breeding strategy,” he says. “The recommended starting point for this is selection based on the Profitable Lifetime Index (£PLI), with subsequent shortlisting based on the herd’s specific needs.”
The mastitis evaluation will be published for all dairy breeds and for daughter-proven and young genomic sires.