30 August 2002

Gene mutations lead to increase in ewe litter size

HIGHER ovulation rates in ewes inheriting certain genes can lead to increased litter sizes of between half and one lamb/ewe, according to research undertaken by Seamus Hanrahan, of Teagasc Research Centre, Co Galway.

"Using DNA technology, we have found two distinct genes with a large effect on ovulation rate in sheep. Two different mutations have been found in one of these genes and one mutation was found in the other," says Dr Hanrahan.

Ewes which inherit a single copy of any of the three mutations will have a higher ovulation rate. However, ewes inheriting two copies of any of these gene variants are sterile, because development of the follicles in the ovary is unsuccessful.

"One of the genes is on the X-chromosome and so can only be inherited from the mother, but the second gene can be inherited from either parent."

Although improvements in prolificacy at the lower end of the scale, such as 0.5 lambs/ewe would be practical in Irish and UK flocks, higher levels could create management problems, suggests Dr Hanrahan. &#42