Breeding Strategies for Improving Resistance to Gastrointestinal Nematodes in Wool Breeds of Sheep

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2010: $17,640.00
Projected End Date: 12/31/2012
Region: North Central
State: Ohio
Project Coordinator:
Kathy Bielek
Misty Oaks Farm

Annual Reports


  • Animals: sheep


  • Animal Production: parasite control, livestock breeding
  • Education and Training: on-farm/ranch research
  • Pest Management: genetic resistance


    Our plan for this two year project was to adapt selection methods identified in Katahdin sheep in previous SARE grants to attempt to reduce the parasite burden in our wooled flocks. Work on the project began in May, 2011 and continued throughout the summer of 2011 and 2012. Analysis of the data will be done in the spring of 2013, following the second year of data collection.


    Project Background

    Sheep can be a profitable livestock species for diversified farming operations. However, for those interested in foraged-based production, gastrointestinal nematodes (GIN) that have become resistant to available dewormers are a serious and growing problem. In common with most sheep producers in the North Central region, we have all identified dewormer-resistant parasites in our flocks. Our sustainability and that of the sheep industry depends on utilizing methods of parasite control other than chemical dewormers.

    The Anderson and Rickard farms have been looking for a solution to the parasite problem for years. Management strategies we have tried include severely reducing the number of grazing sheep, rotating anthelmintics, weaning early, moving lambs off grass to stored feeds, rotating cattle, sheep and hay-making to try to produce parasite larvae-free grass, and growing annual crops. Successful control of GIN remains difficult and still requires selective use of dewormers. Dewormer-resistant parasites severely compromise our efforts of control and may force further reduction of sheep numbers or the elimination of sheep altogether from our farms.

    Published research and our work on previous SARE grants has shown that selecting sheep with genetic resistance to parasites is possible and has the potential to reduce parasite challenge to a flock. Sheep considered genetically resistant to GIN have the ability to suppress or resist the establishment of GIN infection. Parasite resistance is heritable, and the degree of genetic variability among individuals within some breeds can be high. This provides producers an opportunity to improve overall parasite resistance within flock by selecting individual sires with above average resistance. Hair sheep, including Katahdin, have shown greater parasite resistance than wooled sheep, with innate and early-acquired immune responses.


    Kathy Bielek, Misty Oaks Farm. The Bieleks are registered Katahdin seedstock producers with a flock of 30+ ewes. With the aid of previous SARE grants, they have been successful at identifying and selecting sheep resistant to gastrointestinal nematodes (GIN). They provided three of the rams used by the Rickards in this project. She is a member of the Ohio Sheep Improvement Association (OSIA), Katahdin Hair Sheep International (KHSI), National Sheep Improvement Program (NSIP), Ohio Ecological Food and Farming Association (OEFFA), and is past-president of the Ohio Heartland Sheep Improvement Assoc. (OHSIA). Kathy acted as coordinator for the project.

    John Anderson, Lambshire Polypays. The Andersons have a three generation sheep farm established in 1986 with 100 registered Polypay ewes in a pasture-based production system. They supply maternal genetics to the commercial sheep industry as well as registered Polypay seedstock and market lambs. They chose to assess the methods mentioned above for identification and selection of parasite resistance in their purebred Polypay flock. John is a member of OHSIA, NSIP and serves on the OSIA Board of Directors.

    Bruce Rickard, Fox Hollow Farm. The Rickard’s family-owned farm was established in 1987 as a commercial sheep operation peaking at about 950 ewes in 1997. They reduced their ewe numbers to about 350 and added other livestock to become more diversified and help manage GIN. They use intensive grazing techniques, and meat animals are finished on forage. They purchased four Katahdin rams with parasite resistant genetics, to begin to increase genetic resistance to GIN in their flock. Bruce is an OEFFA member and served on the Advisory Board for Graze magazine.

    Eric Shaver, DVM, East Holmes Veterinary Clinic. Dr. Shaver owns a small flock of commercial Polypay ewes, and is owner of a successful five-veterinarian mixed animal practice. About half of his practice is large animal and approximately 75% are Amish, a group with a strong interest in adding sheep to their farms. Dr. Shaver is committed to providing education to shepherds on small ruminant health issues. His clinic performed the fecal egg counts. He supervised several veterinary student interns who assisted with the project.


    * William P. Shulaw, DVM, MS, Extension Veterinarian, Beef/Sheep, The Ohio State University.
    * Charles Parker, PhD, Professor emeritus, Dept. of Animal Science, The Ohio State University.
    * Jeff McCutcheon, Agricultural Extension Educator, OSU Extension Morrow County.

    Drs. Shulaw and Parker helped develop the protocol and provided ongoing advice and support on flock parasite control and genetic selection during the project and provided input in analyzing the results. Dr. Shulaw also helped with education and outreach efforts.

    Tom Wittum, MS, PhD, The Ohio State University. Dr. Wittum provided the statistical analysis.

    Donna Stoneback, Wade Jean Farm. Ms. Stoneback is a Katahdin seedstock producer who provided one of the rams used by the Rickards in this project. She also assisted with collections.

    Richard Ehrhardt, PhD, Small Ruminant Extension Specialist, Michigan State University served in an advisory role and exchanged low FEC crossbred ram lambs as part of a five producer group. His lab also performed the FEC for the third and fourth collections for the Anderson farm in 2012.

    Project objectives:

    Our plan for this two year project was to adapt methods identified for selecting sheep with improved resistance to GIN in Katahdin sheep in previous SARE grants to attempt to reduce the parasite burden in our wooled flocks. Our specific objectives were to:
    1. Demonstrate that progeny of Katahdin rams that had been selected for their genetic resistance to GIN, are likely to have lower fecal egg counts (FEC) than their wooled contemporaries and can be effectively used to increase overall genetic resistance to GIN in a commercial wooled flock;
    2. Demonstrate the same methods used to identify resistant sires in Katahdin hair sheep can be used to identify more resistant sires in a purebred Polypay wooled flock; and to
    3. Develop a blueprint for other sheep farmers (purebred or commercial, hair or wool) to reduce the parasite burden in their flock by the use of parasite resistant sheep.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.