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

Final Report for FNC10-794

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
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Project Information


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.


Click linked name(s) to expand/collapse or show everyone's info
  • John Anderson
  • Jefferson McCutcheon
  • Dr. Charles Parker, PhD
  • Bruce Rickard
  • Dr. Eric Shaver, DVM
  • Dr. William Shulaw
  • Donna Stoneback


Materials and methods:

On both farms, all the test lambs were ear-tagged at birth, identified by sire, and managed the same on common pasture. At each fecal sample collection date for lambs, the following information was collected and recorded: FAMACHA score, body condition score, and weight. Lambs were dewormed based on FAMACHA score and all test lambs that required deworming at any time were recorded. Whenever possible, dam ID, birth date, age of dam, and type of birth and rearing 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 these 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 FEC on randomly selected, fresh fecal samples. Samples were collected from 30 randomly selected ewes per farm (two groups of 15) in early June, for composite FEC to estimate pasture contamination. 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.

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. 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 the ewes on both farms and for the Rickard lambs. Individual FEC were performed on all of the Anderson lambs at each date.

To accomplish our objectives, work on this grant started with breeding decisions made in the fall of 2010. On the Rickard farm, four Katahdin rams (three ram lambs and one mature ram) were purchased based on their documented genetic resistance to GIN. Fecal egg count data as lambs were available for all four rams, and the mature ram had fecal egg count data on his offspring as well. For year one, 21 mature ewes were bred to each of the three Katahdin ram lambs, and 60 mature ewes were bred to the 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.

During lambing in the spring of 2011, the Rickards used different color ear tags to identify potential test lambs (both the Katahdin-cross and wooled controls) that were twin born and reared, out of mature ewes to ensure as much consistency as possible. At the first collection date (June 1), the Rickards provided a list of ID numbers for lambs that met the selection criteria for each Katahdin sire and the two control groups. While fecal samples from only 15 lambs per sire group (90 lambs total) were needed at each date for the composite FEC, twenty test lambs per Katahdin sire and forty control wool lambs were identified in case some of the lambs turned up empty at the times of collection. The test lambs were randomly chosen as the first twenty lambs from each sire on the list of potential Katahdin-cross lambs and the first forty from the list of control lambs to enter the chute on the first collection date, for a total of 120 test lambs. Different color marking crayons were used to identify the test lambs, one color per sire or control, and the same group of test lambs was used for each collection.

The FAMACHA score, body condition score and weight were collected on all of the test lambs at each collection date. Fecal samples were collected from the first 15 lambs from each Katahdin sire and first 30 control wool lambs at each collection date. Composite FEC on the lambs were planned 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. Actual dates of collection were: June 1, June 28 and July 27, 2011. Several veterinary interns working with the East Holmes Veterinary Clinic (EHVC) were trained to assist with the FAMACHA and body condition scoring, and fecal collection. On June 1, fecal samples were also collected from 30 randomly selected ewes (two groups of 15 each) for composite FEC to estimate the level of pasture contamination as an aid in planning future grazing decisions. All the fecal samples were held in a cooler filled with ice, protected from direct contact with ice by a thin layer of newspaper, transported the same day, and stored in a refrigerator at the EHVC. The composite FEC were performed within two days.

Although we had planned to continue the work in the Rickard flock in year two, the realities of on-farm management got in the way. In the fall of 2011, based on the data obtained through this grant, the Rickards made the decision to use only Katahdin rams to sire all their 2012 lambs and sold all their wool rams. While this made sense from a management standpoint, it left us with no control group. To further complicate the issue, the 50% (F1) Katahdin lambs (all born to mature ewes) were born in March 2012, and the 75% (F2) Katahdin lambs (all born to yearling ewes) were born in May. It was felt that with so many variables, the data collected would be difficult at best to interpret and, with SARE’s approval, we decided not to waste valuable SARE resources and farmer time by doing additional collections on the Rickard farm.

For year one on the Anderson farm, six registered Polypay rams with unknown FEC were each bred in the fall of 2010 to 4-10 registered Polypay ewes for lambing in May 2011. Three of these rams were from the Anderson flock and three were from outside flocks. Ten ewes in the flock had been identified as having lower FEC through work on a previous SARE grant (LNC08-306). Ewes lambed on pasture in 2011 as planned, and lambs were identified at birth using the Andersons’ standard tagging system. Collection dates were July 4 and August 19, 2011 (at approximately 8 and 14 weeks of age). Fecal samples were collected on all of the ewe and ram lambs per sire for a total of 61 lambs; wether lambs were not included. Since one of our goals was to establish the variation in FEC in this purebred flock and to identify individual progeny with lower GIN infestation, FEC were done on individual lambs. As at the Rickards, collections were done with the assistance of veterinary interns, samples were held in a cooler and transported to a refrigerator at East Holmes Veterinary Hospital, and read within two days.

During the summer of 2011, John Anderson began working with Dr. Charles Parker, one of our advisors for this project, on a plan to introgress parasite resistant genetics from Florida Native wooled sheep into a subset of his flock. Florida Natives are a small wool breed known for superior parasite resistance. John decided to purchase four Florida Native ram lambs with documented low FEC. He used two of these in his flock while providing two others to cooperating breeders for breeding in the fall of 2011. The two Florida Native ram lambs were each mated to six mature Polypay ewes. In addition, John chose to use one Polypay ram lamb from his flock (L1130R) that was identified with a lower FEC as a lamb in 2011 for breeding that fall. Four mature Polypay rams from outside flocks with unknown parasite resistance were chosen for their superiority in other traits and acted as controls. Again, some of the ewes used for breeding had low FEC as lambs.

In 2012, as in the previous year, ewes in the study lambed on pasture and lambs were identified at birth using the Andersons’ standard tagging system. The two planned collection dates were July 1 and July 31, 2012 (approximately eight and 12 weeks of age). Fecal samples were collected on all of the ewe and ram lambs for a total of 86 lambs. Collections were again done with the assistance of the EHVC veterinary interns, samples were held in a cooler and transported to a refrigerator at EHVC, and read within two days. In addition, with the unused funds available from the Rickard’s second year, it was decided to obtain a fall FEC sample. Since ram and ewe lambs had been separated by that time, ram lambs were collected on September 26 (3rd collection) and the ewe lambs on October 23 (4th collection) using the same protocols.

In both years, all the test lambs on the Anderson farm were dewormed following the first and second FEC collections. Lambs were weaned after the first collection. It was felt that deworming all the lambs would be the safest approach, since counts at that time tended to be quite high. To avoid selection for resistant parasites, the lambs were grazed on pasture that had been grazed previously by mature dry ewes to hopefully provide some, but not an overwhelming, challenge. After the second collection in year one and the third collection in year two, selective deworming was used and only lambs with a FAMACHA score of 3 or higher were dewormed.

During the first year we noticed differences in the amount of scouring (diarrhea) among lambs on both farms. In an effort to identify possible links to parasite resistance, we added a fecal consistency score and dag score to our data collection in 2012.

Research results and discussion:

Data for this project were obtained during the 2011 grazing season on the Rickard farm, and during the 2011 and 2012 grazing seasons on the Anderson farm. Results will be described by farm and by year below.

On the Rickard farm, four Katahdin sires were used along with multiple wool sires as a single control (K1, K2, K3, K4 and Control). FAMACHA scores and body condition scores and weights were obtained on 101, 120 and 124 lambs at approximately 13, 17 and 21 weeks of age respectively. Fecal samples were collected on 15 lambs per Katahdin sire, plus two 15-lamb wool control groups for a total of 90 lambs at each of the above three ages. All the individual lamb samples for each Katahdin sire (or control group) were measured and combined into a single composite sample by sire (or control). There were four Katahdin composites and two control composites at each collection date. Four slides per composite were prepared and read to arrive at the FEC composite average for each Katahdin sire or wool control at each age.

Dr. Tom Wittum provided the data analysis using Oneway Anova. He first analyzed the difference in the Rickard data among individual Katahdin sires and the wool control groups (Table 1). The statistical analysis showed no significant difference in FAMACHA scores, body condition scores or weights among Katahdin sires or among Katahdin sires and the wool control groups.

Because we used composite fecal egg counts instead of individual counts, we were not able to use statistical analysis for the fecal egg counts. However, there were observed differences among individual Katahdin sires and the wool control groups (Table 2). There was an observed correlation among post-weaning (120 day) FEC EBV of the Katahdin sires and the FEC of their offspring at the last collection (average 120 days of age), supporting the importance of using FEC EBVs to identify parasite resistant sires.

We then decided to combine the four Katahdin sires and compare that average FEC to the wool control group for each of the collection dates. The observed differences were much more obvious, with the Katahdin average significantly lower than the control (Table 3).

On the Anderson farm in 2011, six Polypay sires were used (P11-1, P11-2, P11-3, P11-4, P11-5 and P11-6). FAMACHA scores, body condition scores and weights were obtained on 61 lambs when lambs averaged 8 and 14 weeks of age. Fecal samples were collected and individual FEC performed on all 61 lambs at each collection date. Lambs in this group were sired by six sires with 17, 4, 11, 5, 16 and 8 lambs respectively. There were no significant differences among sires on body condition score or weight at either date. FAMACHA scores showed a significant difference among sires at the first date. There appeared to be a difference in FEC among sires at the younger date, but the analysis was unable to detect it statistically. There were statistical differences in fecal egg count at the older age (Table 4). The first analysis of the data compared all six sires. Then the analysis was run again using only the four sires with eight or more offspring. The results were similar both ways.

On the Anderson farm in 2012, five Polypay and two Florida Native sires were used (P12-1, P12-2, P12-3, P12-4, P12-5, F12-1 and F12-2). FAMACHA scores and body condition scores were obtained on 86, 84 and 60 lambs when lambs averaged 8, 14 and 20 (24) weeks of age respectively. Weights were obtained at 8 and 14 weeks. Fecal samples were collected and individual FEC performed on all lambs at each collection date. In addition, fecal consistency scores were obtained at the 8 and 20 week dates and dag scores were obtained at the 14 week collection. Lambs in this group were sired by five Polypay sires with 33, 5, 4, 13 and 4 lambs respectively, as well as offspring of two Florida Native rams (F12-1 and F12-2) with 17 and 10 lambs each (Table 5).

Again, we saw no significant differences among sires on body condition score or weight at either date (Table 5). FAMACHA scores showed marginally significant differences among sires on the first date, but not at the 14 or 20 week collections. Initially we compared all seven sires. There were statistical differences among sires on fecal consistency and dag scores at each date (Table 6). There were observed FEC differences among sires at the first two collections, but the analysis was unable to detect specific pairwise comparisons among rams. The FEC results among sires were statistically significant at the third date (ram lambs), but not at the fourth date (ewe lambs).

The analysis was run again using only the two sires with more than 10 offspring plus the combined Florida Native sires for counts of 33, 27 and 13 (Table 7). This time, FAMACHA scores were marginally different at 8 weeks and statistically different at 14 weeks. There were again no differences in body condition scores noted among sires at any age. However, this analysis showed significant differences in weights among sires at both the 8 and 14 week ages. Statistical differences were noted at all ages on fecal consistency and dag scores. Again, there were observable differences among the mean FEC at the first and second sample dates, but the analysis was unable to detect specific pairwise comparisons among sires. At the third sample date, the differences in FEC were statistically significant. The last collection showed observed differences but they were not statistically different (9, 13 and 3 lambs respectively).

FEC data from the Anderson farm in both years of this study were submitted to the National Sheep Improvement Program (NSIP). The best tool available to sheep producers in the U.S. for making genetic progress in parasite resistance is FEC Estimated Breeding Values (EBV) available through NSIP. The FEC EBV (given as a percentage) gives an estimate of the genetic potential for parasite resistance. A value of zero is considered average for a breed, and animals with a negative (or positive) number are considered to be below (or above) the breed average. Although the data set for Polypays is newer, FEC EBVs were generated for the Polypay rams used in our study. The individual FEC EBVs for the Andersons’ rams ranged from -85% (P11-5, well below the Polypay breed average) to +85% (P12-1, above the breed average).

Impact of Results/Outcomes


The Rickards’ main objective in moving to Katahdin genetics was to improve the parasite resistance of their flock in two ways. First, because the Katahdin lambs were expected to be more resistant to the parasites, mortality should be reduced and performance improved. Second, because the FEC of the lambs (and ewes as the Katahdin crosses mature and become part of the ewe flock) are lower, there will be fewer eggs shed on the pasture, greatly reducing the rate of pasture contamination over time.

Realizing that there are differences in animals, even within a resistant breed, the Rickards chose rams with Expected Breeding Values (EBVs) for improved parasite resistance. As expected, we noticed differences, especially on FEC values, among the offspring of the four Katahdin sires at each sampling, with each sire being higher or lower on different dates. On most dates each individual Katahdin sire was lower than the control group on that date, but there was some variation. However, when we compared an average of all the Katahdin-sired lambs to the control, the FEC of the Katahdin-cross lambs were obviously lower than the controls at all dates (Chart 1). This reinforces our observations that there are differences in FEC count over time as individual animals’ immune response is triggered and that overall, the Katahdin cross lambs had lower FEC than the control lambs.

There was no difference in weights among the Katahdins and the controls, suggesting that it may be possible to select for parasite resistance without compromising production. The control group did have minor but statistically significant better body condition scores, probably due in part to breed differences in the base ewe flock.

The statistical difference in FAMACHA scores on 6/28 and 7/27 was consistent with differences seen in FEC on those dates. The fact that there was not a statistical difference in FAMACHA score on 6/1 probably indicates that the FEC counts were too low to be causing much anemia, or the differences were not being reflected yet in FAMACHA scores. We also know from experience that very young lambs are much more difficult to score than older lambs or adult sheep, and this may have been a factor in the early (6/1) data.

The Rickards were pleased with the results obtained in the first year of the grant, and chose to breed all their ewes to the four Katahdin rams for year two, selling all their wool rams. Although this worked well from a management perspective, it did leave us without a control for the second year. It was agreed by all involved that the limited data we were likely to obtain wouldn’t be worth the work and expense, so the funds were used instead to expand the work done on the Anderson farm in year two.

The main objective on the Anderson farm was to develop Polypay sheep with improved resistance to parasites. FEC as lambs were available on 10 ewes used for the 2011 spring lamb crop through a previous SARE grant, but not on any of the rams. While an innate or early resistance has been observed in hair breeds of sheep, we weren’t sure if we would find this early resistance in Polypays, or in the first cross Florida Natives x Polypays. There were statistical differences among the mean FEC of sire groups at 14 weeks, but not at 8 weeks (Chart 2). This could suggest that innate resistance is not present in this flock, at least at this point in the selection process. However, FEC were very high at the 8 week collection with an overall flock average of 10,816 epg and a range of 1083 epg to 37,700 epg. It is likely that with such high FEC even some of the more resistant lambs were overwhelmed, making differences harder to identify. In year two, there were observed differences among sires at eight weeks, but the analysis was unable to detect specific pairwise comparisons among rams, possibly because some of the sires had so few offspring, or again, the high early FEC may make identifying differences more difficult.

During the course of the grant, additional objectives developed: 1) to assess the feasibility of increasing parasite resistance in young lambs by the introgression of Florida Native genetics; and 2) to compare selecting within an established gene pool to introgression of proven parasite resistant genetics. In the fall of 2011, two Florida Native rams (F12-1 and F12-2), chosen for documented low FEC as lambs in their source flock, were used for breeding along with one Polypay ram lamb chosen for lower FEC as a lamb (P12-4), and four Polypay rams selected for other production traits that served as controls (Chart 3).

At the Andersons, we were able to identify one sire line that had consistently lower FEC. One of the original sires (P11-5) was the sire of ram P12-4 who in turn sired ram P13-1, who in turn was used as a sire for the 2013 lamb crop. Our observation was supported by FEC EBVs which were significantly lower on this line (-82%, -71.7% and -84.8% respectively). The lambs born in 2013 in this line continue to have lower FEC and FEC EBVs than the flock average. We have observed that lambs whose sire and dam had both been selected for parasite resistance had the lowest FEC.

General Observations
The tremendous variation among FEC requires that a minimum number of lambs is necessary to see differences (15 per group has been suggested by Dr. Shulaw). Our experiences confirm that sires with fewer progeny have less accuracy.

In both years and on both farms, body condition score and weight were not statistically different, indicating that these would not make good criteria to use to estimate levels of parasite infection. The differences in weights we observed in 2012 on the Anderson farm were most likely the result of breed differences, rather than differences due to parasites, since the Florida Native is a much smaller breed. This could be a consideration in choosing to use first generation Florida Native genetics in a commercial flock.

The statistical differences in fecal consistency and dag scores that we observed at the Anderson farm seem to support research done in Australia that identified sire differences in scouring in some (not all) parasite resistant lines of sheep. While our sample size is too small to draw conclusions, this is something we will continue to track and be aware of.

Although it is too early to draw conclusions, our work suggests that both approaches we studied have merit. Selecting for parasite resistance within an established gene pool in a wool breed is possible. Initially this approach may be slower with no pre-identified resistant animals, but it will maintain other qualities of the base flock and may be the best approach for many flocks. Introgression of proven genetics from a parasite resistant breed may be faster initially, since the sires used in the first generation will already have resistance. However, it is very important to start with a sire with documented lower FEC or FEC EBVs, not just a breed known for parasite resistance.

The Andersons are members of a consortium of Polypay breeders across five states, OH, MI, IL, IA, MN. All members of this consortium are members of NSIP and submit performance data and make selection decisions based on EBVs. In 2012, in part as a result of this grant, four of the members of the consortium became interested in adding parasite resistance to their selection criteria, at least for a portion of their flocks. John was able to work with NSIP to start submitting data for FEC EBVs similar to those used by the Katahdin breed. In 2013, all four breeders submitted data and got their first FEC EBVs. While it will take time and numbers to develop accuracy, this first step is extremely important and exciting.

Four producers are currently assessing the effectiveness of the introgression of Florida Native genetics for increased parasite resistance in young lambs into crossbred wool sheep. Modeled loosely on the Polypay consortium, this group is performing FEC on lambs, sharing rams and information.

We have found that, like the Katahdin breeders, developing a network of primary breeders to work towards developing parasite resistant sheep is important, whether they are crossbred or registered Polypay. It is anticipated that a model similar to the Polypay consortium where several flocks with common interest combine to have 300-500 ewes and rotate rams, can make the fastest progress while avoiding inbreeding. These producers offer both an example of how to proceed towards developing more parasite resistant sheep, and the importance of cooperation among breeders through the exchange of parasite resistant genetics.

FEC EBVs on registered Polypays are proving to be a useful tool for identifying and selecting parasite resistant sheep on the Anderson Farm. The market for low FEC Polypay genetics is growing. It is expected that this will continue to increase as accuracy increases. At this point (Fall 2013), the registered Polypay have more appeal to ram buyers than the crossbred sheep. We feel this is largely due to a much more commercially acceptable and predictable genetic resource.

  • ? Genetic selection for parasite resistance is possible in wooled breeds and/or sheep with low parasite resistance, but requires commitment and a long term approach.
    ? Introgression of resistant genes is possible by purchasing rams identified as being superior with low FEC from more resistant wool and hair breeds.
    ? An adequate number of lambs (15 per group) is necessary for good accuracy.
    ? A parasite challenge is essential to see differences among animals, but an exceptionally high count can be dangerous and counterproductive.
    ? Body condition score and weight were poor indicators of parasite resistance in our flocks.
    ? Identifying superior rams and rotating among multiple farms helps to avoid inbreeding problems and allows faster progress.
    ? Selecting both ewes and rams with parasite resistance allows the fastest genetic progress.
Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

A fact sheet titled Blueprint for Selecting Parasite Resistant Sheep was developed for use by other shepherds interested in selecting for parasite resistance in their flocks and has already been distributed to attendees at the OHSIA workshop. It will also be made available to OHSIA members, KHSI members and OEFFA members, as well as being posted on the Katahdin NSIP website ( and the Lambshire Polypay website (

Project Outcomes


Potential Contributions

Presentations on selection, 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 attended by 120 people, and at the Ohio Ecological Food and Farm Association’s annual conference in February 2012 attended by 25 people. An open house, which included information on this project, was held at the Rickards in April 2012 with 25 attending. A FEC demonstration was held in June 2012 at the Bielek farm for 12 OHSIA members and results and principles from this grant were discussed. The Ohio Heartland Sheep Improvement Association hosted a workshop attended by 50 participants in September 2013. John and Kathy presented a detailed talk on selection for parasite resistant sheep, and Dr. Eric Shaver presented a talk on parasite management and uses of FEC, including the new composite technique.

Dr. Shaver has adopted the composite technique developed by Dr. Shulaw as a screening tool in his veterinary practice. He thinks it will be a valuable and economical tool for shepherds, allowing more flocks to test levels of parasite contamination, test for anthelmintic resistance, and determine a group average before going to the time and expense of doing individual FEC for selection. This will allow producers to make more informed management decisions and help improve the health of their flocks.

Results have been shared with our cooperators, Dr. Bill Shulaw, Dr. Charles Parker and Jeff McCutcheon for review and use in their Extension activities. Partnering with Dr. Ehrhardt allows us to get information to Michigan audience.

Work will continue through the Polypay consortium and information will continue to be shared with members via email and face-to-face meetings. Marketing of registered Polypay breeding stock with improved parasite resistance will continue to be developed and expanded.

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.