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WHEN first discovered, the Callipyge gene was hailed as the answer to breeding lean, well-muscled sheep, writes MLC sheep scientist Jenny Anderson.
Callipyge means beautiful buttocks in Greek, referring to the enhanced size of the loin and gigot muscles. The naturally occurring gene was first found in American Dorset sheep selected with emphasis on leg conformation, meaning genetic engineering had not been used to manufacture such sheep.
The Callipyge gene is responsible for enlargement of muscle mass via enlarged fibres in the hindquarters, loin and shoulder of sheep when compared to normal sheep. Sheep expressing the Callipyge gene have the leanness, muscling and dressing percentage advantages that are required to attract carcass quality premiums.
However, the gene has never been widely accepted or used in commercial breeding programmes. Its major negative effect is increased toughness in some muscles. Meat from the loin of Callipyge sheep was shown to have much higher shear-force values, even after ageing for 21 days. This is caused by higher levels of an enzyme inhibitor, calpastatin.
This high inhibitor level means that the meat does not tenderise during distribution and storage like normal meat. Several techniques for tenderising meat from Callipyge sheep have been attempted, but these have never been successful in reducing toughness to an acceptable level.
The Callipyge gene has been in the North American and Australian commercial sheep population at a low frequency for about 11 years. More recently, it was introduced into four British flocks by insemination. This was for experimentation purposes to independently test the genes effects on eating quality.
Lambs carrying and exhibiting the Callipyge gene were compared with non-gene carriers from the same flocks. Results showed that the Callipyge lambs had better conformation, but they proved to be exceedingly tough and unacceptable when eaten.
With such evidence, the MLC and major breed societies are concerned about the presence of the Callipyge gene in Britain, as it is obviously detrimental to eating quality of British lamb, and may damage consumers image of lamb.
A closed meeting was held recently to discuss the Callipyge gene, and use of other possible single genes in Britain. It was decided that a voluntary code of practice should be initiated and adhered to.
By fully researching each single or major gene-carrying breed, these sheep should have no qualities that might disadvantage the sheep industry. Clearly demonstrated long-term positive attributes would be required before the genes were commercially available in Britain. *