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

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

Summary

Our plan for this two year project is to adapt 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, as outlined below. Analysis of the data will be done in the fall of 2012, following the second year of data collection.

Objectives/Performance Targets

Our specific objectives are to:
1. Demonstrate that progeny of Katahdin rams selected for their genetic resistance to gastrointestinal nematodes (GIN), are likely to have lower fecal egg counts (FECs) than their wooled contemporaries and can be effectively used in a commercial wooled flock to increase overall genetic resistance to GIN in the flock;
2. Demonstrate the same methods that were successful in identifying resistant sires in Katahdin sheep can be used to identify more resistant sires in a purebred Polypay flock.
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.

To accomplish our objectives, animals had to be bred in the fall of 2010. On the Rickard farm, four unrelated Katahdin rams (three ram lambs and one mature ram) that had been selected for genetic resistance to GIN were purchased. By sampling statistically significant numbers of lambs with the same sire under the same management, published research and our previous work have shown it is possible to estimate the sire’s ability to transmit parasite resistance to his lambs. For year one, 21 mature ewes were bred to each of the three Katahdin ram lambs, and 60 mature ewes were bred to one mature Katahdin ram for lambing in March 2011. The remainder of the flock (approximately 180 ewes) was exposed to wooled rams in a group breeding situation, so individual sires were not identified. Fifteen test lambs were to be identified per Katahdin sire plus two 15-lamb control groups from the wooled sires for a total of 90 lambs. Composite FECs on the lambs were to be done on each sire group at 8-10 weeks of age (estimated to be early June), then monthly through August, the time of heaviest challenge, for a total of three sample dates.

For year one on the Anderson farm, five registered Polypay rams were bred to 8-10 ewes each for lambing in May 2011. Using the timing described above for a total of two sample dates, fecal samples were to be collected on 12-15 randomly selected lambs per sire for a total of 60 lambs. It is important to establish the variation in FECs in this purebred flock and to identify individual progeny with lower GIN infestation, thus FECs were done on individual lambs. Two ram lambs with lower FECs in year one were to be identified as potential sires for the second year lamb crop and compared to some of the original rams using the same protocol.

Accomplishments/Milestones

All the test lambs were ear-tagged, identified by sire, and managed the same on common pasture on both farms. At the Rickard farm, in order to insure that 15 fecal samples per sire were obtained at each sample date, twenty test lambs were identified per Katahdin sire plus two 20-lamb control groups from the wooled sires for a total of 120 lambs. Composite FECs on the lambs were done on each sire group on June 1 (approximately 8-10 weeks of age), June 28th and July 27th for a total of three sample dates. Also on June 1, samples were collected from 30 randomly selected ewes (two groups of 15) for composite FECs to estimate pasture contamination.

At the Anderson farm, samples were obtained from 30 randomly selected ewes (two groups of 15) on June 6, and composite FECs were performed to estimate pasture contamination. Fecal samples were collected from all 60 lambs on July 4 and August 19.

At each fecal sample collection date for lambs, the following information was collected and recorded: FAMACHA score, body condition score, and weight. All lambs in the sire groups that required deworming at any time were recorded. Whenever possible, dam ID, birth date, age of dam, and type of birth and rearing, and weights were also recorded. The data were maintained by the Bieleks in an electronic database. Periodic reports were provided to all participants and cooperators.

Past experiences on theses two farms have shown it is possible for the pasture contamination to be so severe that it would overwhelm even naturally resistant lambs. On both farms, levels of pasture contamination were estimated by monitoring worm egg output by ewes using composite FECs on randomly selected, fresh fecal samples on the dates above. Based on these data and previous information collected on these farms, grazing management strategies and selected deworming were used to provide overall flock parasite control while still providing sufficient worm challenge to measure differences in lamb groups.

Individual and composite fecal egg counts were performed by East Holmes Veterinary Clinic (EHVC) using the McMaster technique. A composite fecal egg counting technique developed by Dr. Shulaw was used to estimate a group average FEC for all the ewes and the Rickard lambs. Individual FECs were performed on all of the Anderson lambs at each date. Four veterinary or pre-vet students working with EHVC over the summer assisted with on-farm sample collection and then assisted one of the EHVC licensed technicians in performing the FECs.

Impacts and Contributions/Outcomes

Presentations which included the work on this grant were given by John Anderson and Kathy Bielek at a field day held on the Anderson farm in August 2011 and at the Ohio Ecological Food and Farm Association’s annual conference in February 2012. Preliminary results were shared with our cooperators, Dr. Bill Shulaw, Dr. Charles Parker and Jeff McCutcheon for review and possible use in their Extension activities.

Collaborators: