Selecting Sheep for Parasite Resistance

View the project final report

• 2006 annual report

Commodities

• Animals: sheep

Practices

• Animal Production: housing, parasite control, preventive practices, grazing - rotational
• Education and Training: extension, networking, on-farm/ranch research
• Sustainable Communities: sustainability measures

PROJECT BACKGROUND
Ten producers from three states (Ohio (7), Missouri (2) and Pennsylvania (1)) chose to work together on this NCR-SARE project. Nine of the producers raise Katahdin Hair Sheep, while one compared a Katahdin ram to a Hampshire ram on mixed Dorset ewes. Flock sizes ranged from 11 to 900+ ewes. Seven of the producers have registered Katahdin flocks, while three have commercial flocks. All the farms are forage based, and use sustainable practices such as rotational grazing and selective deworming strategies. Specifically, the following farms participated in this project:

Kathy and Jeff Bielek, Misty Oaks Farm, Ohio. Kathy and Jeff have a registered flock of 20 ewes on 10 acres of pasture, and lamb in late March. They used 3 rams and 20 ewes for this proposal.

Jim Orr, Orr Farms, Ohio. Jim has a commercial flock of over 900 ewes on 400 acres of pasture, and lambs in May. For this project he used 4 rams and 80 ewes.

Bill Pope, Ohio. Bill has a commercial flock of 56 ewes on 86 acres of pasture, and lambs in May. He used 3 rams and 56 ewes for this proposal.

David Coplen, Birch Cove Farm, Missouri. David has a registered flock with 50 ewes on 32 acres of pasture. His flock lambed in two groups, one in February and one in April. For this proposal he used 4 rams and 50 ewes.

Doug and Mary Emrick, Lazydae Farm, Ohio. Doug and Mary have a registered flock of 11 ewes with 40 Angus cattle on 190 acres. They lamb in April. For this project they used 2 rams and 11 ewes.

Leah Miller, Bluebird Hill Farm, Ohio. Leah has a flock of 30 commercial Dorset ewes on 18 acres of pasture and has decided to add some Katahdin genetics to her flock. She lambs in March. For this project she used 2 rams (1 Hampshire and 1 Katahdin) and 30 ewes.

Richard Gilbert, Mossy Dell Farm, Ohio. Richard has a flock of 50 registered and commercial ewes on 16 acres of pasture, and lambs in April. For this project he used 4 rams and 50 ewes.

Sue and Dave Ingram, DSI Katahdins, Missouri. Sue and Dave have a registered flock of 70 ewes on 78 acres of pasture, lambing in February/March. For this project they used 3 rams and 67 ewes.

Donna and Doug Stoneback, Wade Jean Farm, Pennsylvania. Donna and Doug have a flock of 55 registered and commercial ewes on 34 acres of pasture, lambing from February to April. For this project they used 4 rams and 39 ewes. While outside the North Central region, they have used parasite resistance in their selection criteria for replacement animals for several years, and added important information.

Naomi and Dean Hawkins, Pleasant Pastures Farm, Ohio. Naomi and Dean have 26 registered ewes on 3.5 acres of pasture, and lamb in April. For this project they used 2 rams and 26 ewes.

A total of 456 lambs and 31 rams were used in this project.

PROJECT DESCRIPTION AND RESULTS
Our objectives in this project were to:
1) Identify rams with the ability to transmit resistance to gastrointestinal parasites to their offspring;
2) Compare how different management systems affect the offspring of closely related rams; and
3) Investigate a “farmer friendly” method to identify potential replacement seed stock that most producers can incorporate into their own flocks.

The method we tested included the use of FAMACHA (a way of classifying sheep based on their level of parasite-induced anemia), body condition scoring, vigor scoring, and deworming history on all the lambs, with fecal egg counts (FEC) done on a randomly selected subset of 15 lambs per sire. Selecting animals that demonstrate resistance to gastrointestinal parasites can be done using FEC, while FAMACHA provides a good indicator of resilience. Body condition scoring provides a way to identify very thin lambs that are more likely to carry heavy worm burdens and to become severely anemic. Lambs with heavy worm burdens tend to be less vigorous and more lethargic than other lambs, so a vigor score was added to the protocol as another possible means of identifying more vigorous and potentially more resistant lambs. A history of all dewormings of individual lambs was maintained, as animals with less resistance to parasites were assumed to require more frequent dewormings than their contemporaries.

All the lambs were identified by sire but managed together in a single group on common pasture on each farm. No changes were made in the management of individual farms. Lambs were monitored regularly using FAMACHA and drenched based on the typical management of each farm. In addition to sire ID, the following information was collected on each lamb whenever possible: sex, birth date, birth weight, type of birth and rearing, deworming history, dam ID and age of dam.

Fecal egg counts, FAMACHA, body condition and vigor scores, and weights if possible, were collected at least twice on each farm: at 8-10 weeks and 12-14 weeks of age. All lambs in the sire groups that required deworming at any time before or during the test period were recorded.

The data were sent to the Bieleks after each collection date, where it was recorded and maintained in an electronic database. Periodic reports were provided to our collaborators, Dr. William Shulaw and Dr. Charles Parker.

William P. Shulaw, DVM, MS, and Charles Parker, PhD, have been involved with this project from the beginning. Dr. Shulaw is the State Extension Veterinarian in beef and sheep at The Ohio State University, while Dr. Parker is professor emeritus, Department of Animal Science, at The Ohio State University. Dr. Shulaw and Dr. Parker helped develop the monitoring plan and provided input in analyzing the results.

Our work evolved beyond the original scope of the grant. Dr. David Notter, Professor of Animal Science at Virginia Tech became interested in the project and agreed to perform a genetic analysis on our results. Dr. Notter directs the National Sheep Improvement Program Genetic Evaluation Center at Virginia Tech.

All fecal egg counts were performed by the Parasitology Department of the Virginia-Maryland Regional College of Veterinary Medicine (Virginia Tech).

A preliminary analysis of the results was completed by Drs. Shulaw and Parker and Kathy Bielek in August 2006. Then, a group meeting was held in early February 2007 with our collaborators, Dr. William Shulaw and Dr. Charles Parker and eight of the ten farmers (one joining by conference call). Dr. David Notter, Professor of Animal Science at Virginia Tech attended and shared the results of his data analysis. In addition, Dr. Jim Morgan was able to join the group as a representative of both the National Sheep Improvement Program and Katahdin Hair Sheep International (KHSI). This meeting allowed us to share results and experiences, and to review and discuss Dr. Notter’s analysis of the data. It was a very educational and worthwhile experience for all concerned.

Everyone at the meeting agreed that additional data would be helpful and interesting. Since there were some funds remaining in the project budget, the group agreed to use the funds (with approval from SARE administration), to continue the work for an additional year. Only four of the ten flocks met the original criteria of at least two rams bred to produce contemporary lamb groups. These four farms, Misty Oaks, Wade Jean, Birch Cove and DSI Katahdins, agreed to follow the same protocol during the summer of 2007: collecting weights, body condition score, and FEC on lambs. FECs were again submitted to Virginia Tech for testing.

The following conclusions were summarized from Dr. Notter’s final report on the project. His report is included as an addendum to this report.

CONCLUSIONS
These results suggest that:
• Fecal egg counts taken at average lamb ages of 13 wk or greater showed clear sire differences. The estimate of heritability at these ages was 0.52, which was consistent with the estimate of 0.54 obtained from NSIP Katahdin flocks and considerably larger than the estimates obtained from various wool breeds around the world. Thus selection to reduce FEC in Katahdin lambs at ages of 13 wk or more should clearly be successful.
• At all ages, there was a strong positive association between FEC in full-sib littermate lambs. This result suggests that lambs born to the same ewe have similar FEC, both early (8-wk) and later (after 13 wk) in life.
• Lambs with high FAMACHA scores tended to also have higher FEC, but the relationship was not very strong, with correlations of only about 0.30 between the two variables. Sire differences in FAMACHA scores were significant at 13 wk of age, suggesting that selection on FAMACHA score could be effective but would likely produce considerably slower changes in FEC than direct measurement and selection.
• Body condition and lamb vigor scores were positively associated with lamb age and weight and with one another. Sire differences in these scores were not observed at any age. Thus, these scores have some descriptive capability, but it is not clear that they have much to contribute to a program of selection.
• Results from this study are broadly consistent with results of the NSIP Katahdin flocks and lead us to conclude that:
 Selection favoring low FEC will be effective in increasing parasite resistance in Katahdin flocks.
 The age at measurement is likely less important than the level of infection present at the time of data collection. If lambs have a mean FEC of 500 to 1,000 epg or more at the time of measurement, the resulting FEC data are likely to provide useful information for selection to enhance parasite resistance.
 FAMACHA scores are a useful management tool that can be used to identify and selectively deworm those lambs that are at greatest risk from parasitism. FAMACHA scores have a modest positive association with FEC.
 Use of FAMACHA scores alone as a tool for selection to enhance parasite resistance will likely be inferior to selection based directly on FEC.
 A combination of recording of FAMACHA scores to monitor levels of parasite infection and recording FEC as a selection tool may be the optimal strategy for improving genetic resistance to internal parasites.

Thanks in large part to the involvement of Dr. Notter, the results of this project far exceeded our original expectations. His statistical analysis provided a level of accuracy not attainable through our analysis of the raw data.

As we had hoped, we were able to identify several rams that showed a greater ability to transmit parasite resistance to their offspring. Obvious sire differences were observed on some farms, while on other farms differences were less obvious. Data from both years of this project were submitted to the National Sheep Improvement Program (NSIP) for inclusion in their new fecal egg count (FEC) expected progeny difference (EPD) project. We hope to have results from this analysis later this fall (2007) that will provide more specific predictions of this resistance.

We were able to show and observe that management practices had a significant impact on parasite levels. While these differences often made analyzing the raw data difficult and confusing, it suggests that there are many simple strategies that can be used in the average flock to help reduce the effect of parasites. Some observations include:

• FAMACHA is a valuable tool in selective deworming, but is time consuming and takes practice to achieve accurate results
 Good lighting is essential
 Young lambs are harder to score than older lambs or adult sheep
 Color blindness in the handler can be a problem
 FAMACHA gets easier (& more accurate) with practice

• Pasture and parasite conditions change through the year
 Contamination increases, often quickly, through the summer
 Heaviest parasite pressure: June – September in Ohio
 Lambs that were consistently rotated to clean pastures had dramatically lower FECs than lambs that were rotated over the same pastures throughout the summer

• Nutrition and age are important
 Single lambs born to mature ewes typically had lower FECs than twins; twins typically had lower FEC than triplets

 Lambs born to yearling ewes, especially twins, often had higher FECs than lambs born to mature ewes
 Heavier lambs tended to have lower FECs than lighter lambs in the same group
 Older lambs had a lower average FEC than younger lambs grazing the same pasture

We were also able to achieve our final objective - to investigate a method to identify potential replacement seed stock. Every farm was able to identify individual animals that appeared to be more parasite resistant than their contemporary group.

We found that FAMACHA, body condition scoring and vigor scoring all could be indicators of parasite challenge, and could be useful in a selective deworming program. Our analysis of the raw data, and Dr. Notter’s statistical analysis, suggests that of these methods, only FAMACHA was useful for selecting replacement stock. However, FEC is the most accurate method of identifying resistant animals, and therefore the fastest for making changes in the flock.

Some other things we learned or had reinforced about this process were:

• Adequate numbers of lambs are necessary for good selection of replacement stock
 There are significant variations in FEC among lambs, even from the same parents
 Total of 15 lambs per sire is ideal; minimum of 10 lambs per sire is needed for accurate comparisons

• Parasite challenge is critical
 A flock average of at least 500 epg, and preferably 1000 epg, is needed to ensure adequate challenge
 Time of year seems to be the most important factor, with higher counts seen from June-August

• Contemporary groups are important
 Lambs of different ages are difficult to compare, even on the same farm

OUTREACH
Preliminary results have been shared at the following:
• Farmers Forum at the Small Farm Trade Show & Conference in Columbia, Missouri, November 4, 2006. (20 participants)
• Producers group meeting with Drs. Shulaw, Parker, Notter and Morgan, Columbus, Ohio, February 3, 2007. (12 participants + 3 via conference call)
• Ohio Ecological Food and Farming Association (OEFFA) Annual Meeting, Granville, Ohio, March 4, 2007. (20 participants)
• Ohio Sheep Day, Wooster, Ohio, July 14, 2007 (25 participants)
• FAMACHA training program, Wade Jean Farm, Quakertown, PA, October 13, 2007 (40 participants)

Fecal egg count, FAMACHA and performance data have been shared with Dr. William Shulaw for use in his extension work and publications. In addition, Dr. David Notter has used the data obtained in this project in various presentations.

The preliminary results were shared with the Midwest Katahdin Hair Sheep Association for inclusion in their fall newsletter. A final report will be shared with the Katahdin Hair Sheep International (KHSI), the Ohio Sate University Sheep Team and Ohio Ecological Food and Farming Association (OEFFA) for inclusion in their newsletters. A summary of the project is planned for The Shepherd magazine, a prominent trade journal.