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Having too few brain receptors for a hormone could be a new-found
reason
why eight to 15 percent of sheep rams are reluctant to mate with ewes--and
thus costly to ranchers. Results of a recent study by ARS scientists
and cooperators suggest that rams with enough receptor molecules respond
to the hormone estrogen's chemical signal, stimulating them to mate with
ewes. The discovery is part of research that could lead to a test
enabling sheep ranchers to evaluate a ram's breeding potential, and avoid
losing money on reluctant rams. Scientists examined eight ewes and eight
rams, including four that would only mount other rams. They counted
estrogen receptors in the amygdala, a part of the brain that's thought to
influence sexual behavior. The findings are the first evidence in any
animal species that brain chemistry may influence sexual orientation.
Range Sheep Production Efficiency Research, Dubois, ID
John N. Stellflug, (208) 374-5306
St. Croix sheep can produce three to six lambs every 24 months rather
than
the typical one to two lambs per year from traditional breeds--a 33
percent gain in productivity. Most sheep breed in September or
October and give birth in February or March--too late for lambs to reach
the desired market weight of about 110 pounds by the prime Easter sales
season. But St. Croix sheep will breed year-round, so producers can time
lambings to make the most of the market. In three years of field tests in
Arkansas, groups of St. Croix ewes were bred at two-month intervals
throughout the year. Lambing percentages--the percentage of bred females
who subsequently gave birth--were in the high 80s for animals bred in
October through January and the low 70s for animals bred in June through
September. The lowest rates were the mid-30s for animals bred in April
and May. Other advantages of St. Croix sheep: They're heat-tolerant and
resistant to stomach worms called nematode parasites that cost U.S. sheep
farmers an estimated $45 million annually.
South Central Family Farms Research Center, Booneville, AR
Michael A. Brown, (501)675-3834
Last updated: November 15, 1996
Return to: Quarterly Report
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Last Modified: 02/11/2002
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