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New Test May Help Increase Sheep Production

By Amy Spillman
March 1, 2002

Traditionally, rams in the United States have been selected for breeding purposes on the basis of how quickly they grow and the size they ultimately attain. Soon, however, farmers may have a way to identify another important breeding characteristic before they make their selection. Agricultural Research Service scientists with the U.S. Sheep Experiment Station in Dubois, Idaho, and their collaborators have developed a test to help identify sexually active male sheep.

Between 15 and 25 percent of all male sheep in the United States may ignore ewes’ mating overtures, a statistic that has major ramifications for the U.S. sheep industry. Breeding rams are usually priced between $200 and $400, and their care and maintenance can run up to $100 per year. Buying just one sexually inactive breeding ram can therefore cost a farmer up to $500; the figure goes up even further when considering lost potential.

Some livestock industries use artificial insemination as a way of sidestepping the problem of variable male libidos, but this approach incurs additional labor costs. Most of those who raise range and farm flocks of sheep prefer to let their animals breed naturally.

The new test--based on research by ARS animal scientist John Stellflug, colleagues at Dubois and collaborators--is based on the premise that libido is closely linked to the ability to secrete testosterone. It measures testosterone response in sires using an injection of naloxone, which blocks certain hormones to stimulate testosterone release. When a male mammal is given an injection, his testosterone response predicts whether he is sexually active or inactive.

This test could impact the sheep industry by helping identify which male sheep are sexually active, thus increasing the reproductive potential of entire flocks. By replacing nonproductive males, the industry could save itself both time and money.

ARS has obtained a patent on this technology and is seeking a company that may be interested in licensing it and developing a commercial product. Because some researchers have speculated that the technology may be effective for testing other species, its potential impact could be high.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

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