Vets, farmers and breeding specialists all agree that avoiding difficult calvings should be a target when making both breeding and management decisions, with the welfare costs to the animal and the financial costs to the farmer of a difficult calving each taking a heavy toll. That's why milk producers have been strongly urged to complete the calving ease survey as part of their milk recording, enabling the industry to gather large quantities of information which can be traced back to each animal's sire.
To date, records from some 400,000 calvings have been collected, which represents information from around 6,000 Holstein and Friesian sires. And now that these records have been assessed, DairyCo is in a position to publish the first ever official UK, independent Calving Ease indexes which will be available to the farming industry with the general sire proof run in January 2010.
The new indexes will be expressed on a scale of around -4 to +4, with a breed average of zero, and with positive figures indicating that calvings are predicted to be easier than average and negative figures predicting more difficult calvings. But there won't just be one calving ease index, there will be two - one for Direct Calving Ease (dCE) and one for Maternal Calving Ease (mCE) - and it's important to be aware of the differences between each one.
"The index for Direct Calving Ease gives a prediction of the ease with which a calf by that sire will be born," says Marco Winters, director of DairyCo breeding+. "And Maternal Calving Ease provides a prediction of the ease with which a daughter of that sire will give birth.
"By considering both indexes, you'll get a complete picture of each bull's 'calving performance', although it will generally be the Direct Calving Ease that's likely to be of most interest in the first instance.
"This is obviously going to be far more so when breeding maiden heifers, where choosing easy calving sires is clearly an important consideration. But it shouldn't be ignored in older cow matings either, where it would always be wise to avoid bulls which are likely to produce very difficult calvings."
The relationship between Direct Calving Ease and Maternal Calving Ease must not be overlooked either as long-term selection for Direct Calving Ease without any regard to Maternal Calving Ease could set up problems for the future.
"It's well known that the two traits are negatively correlated, which means that as you select for good dCE you are likely to worsen mCE, so it's important that farmers pay attention to both of these figures," says Mr Winters.
This would be logical to most cattle breeders, who are likely to associate easy calvings with smaller calves, but whose smaller calves sometimes go on to have difficult calvings themselves. The emphasis breeders are recommended to put on each index varies according to their situation, and as Mr Winters remarks: "If you put a lot of selection pressure on calving ease you would quickly improve this trait but you are likely to lose ground in other important areas."
In reality, he recommends selecting primarily for Profitable Lifetime Index (PLI) and using the Calving Ease indexes - as well as other fitness traits - as secondary criteria, with careful judgement made on a case-by-case basis about their relative importance. And although the traits are not highly heritable (similar to other fitness traits, such as Lifespan), he says worthwhile progress can be made because there is variation between bulls, and - like all genetic improvement - this accumulates over the generations. The industry project which got the index off the ground - which was largely funded by Defra, had additional support from the Scottish Government, DairyCo, NMR, CIS, Holstein UK, Genus ABS and Cogent, and was undertaken by SAC - was led by Dr Mike Coffey. Explaining why it has taken until now to come to fruition Dr Coffey says: "We have had proprietary indexes from Genus ABS and Cogent which many farmers have used, but there has been no real appetite until now for a national programme.
"But now that Interbull [the body responsible for international genetic evaluations] regularly publishes international calving ease indexes we need independent national figures from the UK in order to participate.
"We've been very pleased with the accuracy of the UK data," adds Dr Coffey, "as there have been high correlations between our own figures and those from other key countries, so I'd like to thank farmers for taking the trouble to complete their calving ease surveys and for doing it with obvious accuracy.
"It's extremely important to resist any temptation not to record difficult calvings, as it is only with reliable information that genetic progress can be made."
Remarking that Calving Ease indexes will remain, for the short term, as stand-alone indexes, Marco Winters says: "They may well be incorporated into PLI in the future but for the time being, they won't be included and won't affect the overall rankings.
"And we don't expect many surprises either," adds Mr Winters. "Since Genus ABS and Cogent have collected young sire calving ease data in the UK and many international bulls already have Calving Ease indexes, we already have an idea of how most bulls will score."
But with this additional information now available on an ongoing basis and with the backing of hundreds of thousands of calving records, UK farmers can breed in favour of calving ease with more confidence in the outcome than ever before.