Gene has breeders counting sheep

CORNELL (US)—Discovery of an unusual form of a gene may have sheep breeding like rabbits—all year long.

The gene—M allele—prompts ewes to breed out of season and to conceive at a younger age and more frequently, researchers at Cornell University find.

“The primary biological limit for sheep production worldwide is the seasonality of breeding, but the market for high-quality lamb is a 52-week thing,” says Doug Hogue, professor emeritus of animal science at Cornell.

Researchers warn that while the presence of the M allele gene correlates to the ability to breed out of season, it may only be a marker for the gene that is actually responsible.

“Breeding out of season is a complex trait,” explains former Cornell postdoctoral researcher Raluca Mateescu,  “so there are a lot of genes controlling it.” Mateescu, who coauthored the paper, observed the phenotype—the physical expression of the gene—in the researchers’ flock during a postdoctoral fellowship at Cornell.

“In this case, we’re talking about a receptor gene for melatonin,” explains Mike Thonney, professor of animal science.

Melatonin is a naturally produced hormone commonly found in many animals. The change in the DNA sequence of the M allele does not change the amino acid sequence of the protein.

This means that it may be an accurate indicator for the phenotype of breeding out of season, though it’s uncertain whether the gene actually impacts how the sheep’s body reacts to melatonin. And there may be a risk of losing the association over generations, the researchers say, as recombination could occur between the marker and the functional gene.

Thus, the researchers stress that it will be important to validate the gene’s ability to indicate for aseasonal breeding each time the allele is bred into a new sheep population.

“I think it’s very exciting. We only have one gene, but it’s definitely a tool that farmers can use,” says Mateescu, who is now at Oklahoma State University focusing on placing markers across the sheep’s entire genome to more accurately determine which gene or genes directly affect the trait of aseasonal reproduction.

Researchers believe the M allele discovery will be an important complement to the  STAR system which Hogue and Cornell sheep farm manager Brian Magee developed in the early 1980s which uses nutrition and conventional breeding techniques to reduce the time between heats. Using the STAR system, ewes lamb five times in three years rather than once a year.

“If a ewe doesn’t get pregnant when she is supposed to, instead of a year, it’s only 73 days until she has another opportunity,” Thonney says.

While the STAR system requires better nutrition and more farm labor to manage the lambing, each lambing event involves fewer ewes than traditional yearly lambing. Researchers hope that the discovery of the M allele will help the STAR system adapt to consistently high levels of production without any additional risk to flock health.

The study, which was published in the August issue of the Journal of Animal Science, was supported by the U.S. Department of Agriculture, Oklahoma Agricultural Experiment Station and New York Agricultural Experiment Station.

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