12 September 1997

Unproven bull dispute continues

By Sue Rider

BREEDING company disputes over use of unproven dairy bulls are destructive and come at a time when collaboration, not discord, is needed.

That is the message of independent breeding consultant John Hinks, speaking in response to disagreements which have emerged between two breeding companies over the use of young bulls.

"The main reason for participating in progeny testing is an altruistic one – to get bulls proven – not because it is the best route to increasing profits or genetic gain," he says.

"The best way to maximise genetic progress is to use the top proven bulls, and ideally those with an accurate UK proof.

"Using young bull semen in preference to that from the best proven bulls will cost you in terms of genetic progress and profit."

This was his reaction to a Cogent commissioned report by ADAS, that suggests using young sires on all cows bred to Holsteins will reduce semen costs and help maximise genetic gain.

The ADAS analysis found a strong relationship between the pedigree index or estimated predicted transmitting ability (EPTA) and predicted transmitting ability (PTA).

Based on the findings of the ADAS report, Cogents Wes Blum says that breeders can achieve genetic gain equivalent to or better than the top 20 proven bulls by using a team of elite young sires.

But Genus has condemned the report as grossly misleading and flawed in its calculations. Company breeding director Steve Amies says that the comparison of EPTA and progeny proof (PTA) for the 560 bulls analysed is flawed. Instead of using the EPTA at the time bulls entered progeny testing, the analysis compared Feb 97 progeny test results with the Feb 97 EPTA. This is grossly misleading, he says. "The Animal Model will have adjusted the original pedigree index, taking into account data materialising since the bull entered progeny testing, including its own progeny test."

He also criticises the low reliability of bulls returning with PTAs in Feb 97.

"One would not expect to see much difference between the two sets of data, so it is not at all surprising this is what ADAS found. Had the comparison been made between a bulls EPTA at the time of him being sold as a young bull and when a full, accurate progeny test is returned, the answer could have been very different."

To highlight that the higher the EPTA of the young sire the greater the variation between that and its proof, Genus research and development projects manager Brian McGuirk cites an analysis of 172 bulls from US dams, born between 1987 and 1991.

Average difference between EPTA and PTA (July 96) was £13.2 PIN. Proofs averaged 86% reliability. The higher the average EPTA the bigger the discrepancy. For the top quartile, the average slippage was £20 PIN, he says.

ADASs response is that its findings are in close agreement with other studies from around the world – such as Guelph University in Canada

"As always individual farmers have to strike the right balance between test and proven bulls. That balance will depend on their attitude to risk and economic considerations," says ADAS.

Breeding companies clash over use of young sires to breed dairy heifers.


&#8226 Use as group of at least five.

&#8226 Higher index, higher risk.

&#8226 Top proven bulls give best genetic gain.