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Investing in Parasite Resistance

A recent silent bid sale of USDA ARS Katahdin sheep indicates the importance of parasite resistance to buyers. Ninety-eight ewes and rams were offered for sale: 17 ram lambs, 12 mature rams, 24 ewe lambs, and 45 mature ewes. They were purchased by 13 buyers from 7 states.

A sale catalog was distributed to the public by mail, email, or online. It described the sheep by age, sex, recent body weight, scrapie genotype, hoof color, and National Sheep Improvement Program (NSIP) estimated breeding values (EBVs). The EBVs included traits on parasite resistance, growth, and maternal (or reproductive). The traits were defined and additional information was provided, if inquiries were received. Potential buyers could view animals or request photos.

Of the ram lambs that sold, post-weaning FEC EBVs ranged from -29 to -100, but of the seventeen ram lambs offered, only rams with values of -97 or better sold (-100 is considered the highest resistance EBV and values can reach +500 or more). The highest price ($654) offered for all sheep was on a ram with a FEC EBV of -100. All mature rams sold and their FEC EBVs ranged between -66 and -100 with the highest bids offered to rams with -100.

All but five ewe lambs sold, with FEC EBVs ranging from 33 to -75. Higher prices were offered for ewes with better FEC EBVs. All but six mature ewes sold. Their FEC EBVs ranged from 18 to -87 with higher prices offered for ewes with better FEC EBVs. For all sheep, higher prices were offered for animals raised as multiples rather than singles.

Using FEC EBVs to select for parasite resistance has led to more rapid genetic progress, as demonstrated by the Flock Genetic Trend (weaning FEC EBV or WWEC is presented in bottom right graph). Seedstock producers can benefit by using NSIP to make progress on emphasized traits, whereas commercial producers can benefit by purchasing replacement animals with known EBVs of importance.

The USDA ARS Katahdin flock at the Dale Bumpers Small Farms Research Center in Booneville, Arkansas, has been selecting for parasite resistance using EBVs since 2011 and using fecal egg counts (FEC) since 2004 (see genetic progress).

More information about NSIP can be found at

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