2 August 2002

Avoiding inbreeding in cattle is CVM solution

By Jessica Buss

WHILE many breeding companies have removed bulls carrying the gene causing the deformity CVM from their brochures, Genus believes a better long term solution to the problem is to avoid inbreeding.

Breeding companies deciding to remove bulls carrying complex vertebral malformation (CVM) from their brochures include Semex, Green Acres and World Wide Sires. Bob Hardy of World Wide Sires says it is possible to use CVM bulls when parentage and grand-parentage is taken into account. "But there has been so much use of sires carrying CVM in the UK that few herds will be free of CVM carriers and many will be riddled with it."

However, James Simpson of Genus believes the real problem which must be addressed is inbreeding. "Until a few years ago we werent concerned about inbreeding, providing it remained below 6%. But this is no longer the case with the % of inbreeding in animals increasing in the US, Canada, Holland and France." He suspects it is rising in the UK too.

"We could eliminate all sires with the recessive CVM gene, but its not that simple when their bloodlines are selected because they are the best on performance. CVM bulls tend to be the higher producing bulls when we compare them with their full brothers.

"Ignoring CVM carrier bulls is a short term strategy, with a large number of potential carrier bulls still coming through breeding programmes everywhere."

But even if CVM bulls were taken out of the equation, there are other genetic defects, he adds. Bovine leukocyte adhesion deficiency (BLAD) and Mulefoot are two simple recessive gene disorders which are already known, but more could appear with an increase in inbreeding.

"The best way forward is to manage it out of the system by using CVM carriers with care." But that requires more care when selecting which bulls to use on which cows.

"Currently, many producers use one to three bulls across the majority of the herd each year. But they miss how inbred each generation is becoming." This comes about because cows are served with bulls they are related to in a previous generation.

Reducing inbreeding would increase herd life, adds Mr Simpson. US research shows for each 1% increase in inbreeding, 13 days productive life and 358kg of milk are lost.

Working out the relationships between animals on paper would be too time consuming to contemplate. But Genus new bull mating program – Long Life Breeder – will check these relationships, using its extensive UK database.

"When a CVM carrier is in a cows pedigree, either her sire or grandsire, it eliminates CVM carriers from the suggested mating," explains Mr Simpson. And, because the program minimises inbreeding, it reduces the chance of other simple recessive genes becoming a problem.

The new program requires accurate cow information, including sire and grandsire, but pedigree classification is not essential. Although Genus has trained its breeding advisers to help producers set it up for herds using a potential combination of 486,000 breeding goals, it will be available for producers to use free of charge on the internet.

The website will also make it easy for producers to rerun the program for their herd using bulls selected from the Genus stud. Genus has, however, decided only to include its own bulls for mating to ensure the information is accurate. &#42

Avoiding inbreeding will minimise risks of genetic defects in future dairy cow generations, says James Simpson.

CVM explained

CVM carriers have one CVM gene and appear normal. But they will transmit the gene to half their offspring. If an animal receives one copy of a gene it becomes a carrier. When an animal has two copies of a CVM gene – one from each parent – it will be reabsorbed, aborted or born dead.