(Previously published on the American Consortium for Small Ruminant Parasite Control web page, December 12, 2017)
Since the mid-2000’s, the National Sheep Improvement Program (NSIP) has been providing estimated breed values (EBVs) for parasite resistance. These EBVs have been for fecal egg count (FEC), an indicator trait of resistance. FEC EBVs have allowed producers to select for superior individuals in reducing parasite burden. But do they work?
With the rise of anthelmintic resistance in parasite populations, genetic selection for parasite resistance has been suggested as a means to ensure small ruminant sustainability. Breed differences in parasite resistance have been well established. Caribbean hair sheep (St. Croix, Barbados, etc.) develop a strong immune response which inhibits larval establishment and consequently prevents the clinical signs associated with adult worm infection (anemia, weight loss).
More traditional wool breeds such as the Suffolk have shown greater susceptibility to parasitism. Composite breeds such as the Katahdin have shown enhance resistance with significant variability within breed. Previous work has examined opportunities for cross breeding to improve parasite resistance in more susceptible breeds and enhance growth and carcass merit in hair breeds. While the opportunities for crossbreeding are encouraging, within breed selection for parasite resistance is also possible.
Since the mid-2000’s, the National Sheep Improvement Program (NSIP) has been providing estimated breed values (EBVs) for parasite resistance. These EBVs have been for fecal egg count (FEC), an indicator trait of resistance. FEC EBV’s have allowed producers to select for superior individuals in reducing parasite burden. Both weaning FEC and post-weaning. FEC EBVs are available representing genetic potential for resistance at both 60 days of age and 120-150 days of age, respectively. This technology has been greatly utilized by Katahdin producers and has shown significant potential.
To further validate these FEC EBVs and establish a better understanding of the mechanism behind parasite resistance, West Virginia University, Virginia Tech, and the USDA are collaborating to examine progeny performance in rams differentially selected for FEC. Katahdin rams which have either exceptionally high or exceptionally low FEC EBVs have been sourced from producer flocks. Average differences in post-weaning FEC EBV between the high and low selected rams was over 300%. Rams were paired with Katahdin ewes at the Southwest Virginia Agricultural Research and Extension Center (Glade Spring, VA) to minimize inbreeding and effects of ewe age.
Lambs will be born March 2018 and managed on pasture with their dams until weaning. At weaning, lambs will be relocated to West Virginia University where they will be housed in a dry lot barn. Lambs will be artificially dosed with Barber Pole Worm (Haemonchus contortus) and evaluated for parasitism and growth through a primary and challenge infection. Following infection, lambs will be harvested and carcass composition will be determined. This project will be repeated in 2019.
Effects of sire FEC EBV will be related to progeny performance in terms of both parasitism as well as growth and carcass merit. Additionally, immunological differences in progeny sired by high and low FEC EBV rams will be characterized. This project will help us better understand selection for FEC breeding values and its consequences on lamb parasitism as well as the mechanisms behind this resistance.