The Impact of Estimated Breeding Values on Parasite Resistance and Reduced Parasitism in Sheep

View the project final report

Commodities

• Animals: sheep

Practices

• Animal Production: animal protection and health, genetics, livestock breeding

Infection with gastrointestinal nematodes threatens economic viability of small ruminant production in the South and is the major health concern due to widespread GIN resistance to dewormers. Parasitic worms are a year-round problem in the South affecting well over 1 million sheep on more than 230,000 small to mid-size farms that raise small ruminants in the U.S. Gastrointestinal worms can cause reduced weight gains, anemia and death of infected animals. Because of the high prevalence of dewormer resistance (worms that are resistant to all available dewormers), alternative tools that aid in control of worms are extremely important, including parasite resistant genetics. The National Sheep Improvement Program provides predictable, economically important genetic evaluation information to the American sheep industry by converting performance records into relevant decision-making tools. By using sheep (or goats) with predictable genetics or performance attributes, including growth, reproductive or maternal traits, and parasite resistance, a superior flock can be built for both breeding stock and commercial flocks (which focus on lamb production). The genetic predictability uses estimated breeding values, which are science-based, industry-tested measures of an individual animal. No data exists on the impact of parasite resistant EBVs in sheep flocks. There is a large variability in the marker for parasite infection, fecal egg counts, within a breed. Within the Katahdin breed, FEC EBVs range from -100 to 769 (-100 is the best EBV for parasite resistance), indicating great potential for genetic selection. A sheep with -50 FEC EBV would be expected to have a FEC 25 percent lower (a 50 percent improvement) than progeny from an individual with 0 percent. If you were to mate a ram with -100 percent to a group of ewes, then you would expect FEC of his lambs to be 50 percent lower than FEC of lambs sired by a ram with 0 percent FEC EBV. Flocks that have selected for parasite resistance have markedly reduced FEC in their flocks and have flock averages of -60 to -70 percent. The need exists to disseminate parasite resistant genetics to seedstock and commercial farms and better understand their contribution to sustainable sheep production. A more resistant flock will be less likely to succumb to losses due to parasites and remain sustainable. The practice of genetic selection of superior animals or those that possess parasite resistance will increase the sustainability of existing flock management and will have particular relevance to organic and pasture-based production. We collected data from NSIP flocks to understand the economic benefit of parasite resistant genetics along with superior growth or maternal traits captured by NSIP EBVs and reported their value in terms of farm sales of breeding rams.

The objective is to show producers the value of sheep with high resistance by examining farm gate sales of sheep with EBVs generated by NSIP.