27 July 2001

Double muscling gene brings snags

By Jessica Buss

WHILE increased muscle is desirable, research shows South Devon cattle with the gene responsible for double-muscling also have more calving difficulties, says MLC beef scientist Duncan Pullar.

"The gene responsible for double-muscling, called the myostatin gene, has only been identified in the past few years."

Nearly all Belgian Blue cattle have myostatin gene deletion, which causes changes in many muscle-related traits because the number of muscle fibres produced in the foetus is increased – known as double muscling. The same gene deletion is responsible for double-muscling in South Devons.

Research on the UK South Devon population has revealed myostatin deletion in 37% of the breed, he adds. "But not all of these cattle are visually double-muscled, indicating other genes are involved in controlling muscle conformation."

South Devon cattle with deletion of this gene show increased muscle conformation score, decreased fat depth and have a higher incidence of calving difficulties. But it does not appear to increase 200-day and 400-day weights.

"The presence or absence of the gene appears to account for a high proportion of the way South Devons look and calve," he says.

But the muscle conformation and fat depth values are used to calculate breeding values through Signets Beefbreeder service, which are then used by breeders to make breeding decisions. Therefore, inadvertently, breeders choosing to improve muscling could be selecting for double-muscling and increasing risks of difficult calvings, according to Dr Pullar.

One of the key questions now facing the South Devon Herd Book Society and breeders is whether to select for myostatin deletion to improve muscling or against it to protect the easy calving nature of the breed.

This will involve deciding whether the breed is best suited to producing terminal beef sires or should focus on its maternal traits, says Dr Pullar. "Whatever direction is chosen, genotyping is needed for informed choices to be made in breeding programmes."

But breed society chief executive, Lesley Lewin says it is too early to make such a decision. Roslin Institute researchers who have been doing the work believe there could be other influences affecting the expression of the myostatin gene in South Devons, either genetic or management related, she adds.

"Research needs to continue, which Roslin is seeking further funding for. But at some point the breed may have to decide on a direction."

Currently, she says, the breed is one which is capable of producing suckler cows and terminal beef sires, with some herds specialising in one or the other. "It is suited to use as a suckler cow or as a sire for a herd which wants to produce replacements and finish animals for beef."

There is also a possibility that it could decide to split breed improvement in two directions, she adds. Dr Pullar says that in France the Charolais breed, in which double-muscling also occurs, has begun a separate herd book for double-muscled cattle. These are known as Culard Charolais cattle. &#42

DOUBLE-MUSCLING

&#8226 Genetically controlled.

&#8226 Gene identified at Roslin.

&#8226 Could be related to calving difficulties.

DOUBLE MUSCLING

&#8226 Genetically controlled.

&#8226 Gene identified at Roslin.

&#8226 Could be related to calving difficulties.