Building on Parasite Resistance Selection in Sheep

PROJECT BACKGROUND
Producers participating in this project include:
* Jeff and Kathy Bielek - Misty Oaks Farm – Ohio (Years 1 and 2)
* Donna Stoneback - Wade Jean Farm – Pennsylvania (Years 1 and 2)
* Sue Ingram – DSI Katahdins – Missouri (Year 1)
* David Coplen – Birch Cove Farm – Missouri (Year 2)

For this project, producers from three states (Ohio, Missouri and Pennsylvania) continued work that was started through NCR-SARE grants FNC04-523 and FNC05-583. All the producers raise registered Katahdin Hair Sheep, are forage based, and use rotational grazing and selective deworming strategies. The number of ewes used in this study ranged from 15 to 32 per farm. Each farm used at least two rams each year, some closely related to rams used on other farms.

PROJECT DESCRIPTION AND RESULTS
Process: The goal in this proposal was to continue the work started in NCR-SARE grant FNC05-583, Selecting Sheep for Parasite Resistance. In that grant, ten Katahdin producers worked together to identify sires who produced animals with increased parasite resistance as lambs. In the current grant, three producers involved in the previous work went on to study rams and ewes selected as replacements based in part on their low fecal egg counts as lambs, to assess their adult parasite resistance and that of their offspring. We also investigated methods of identifying ewes with reduced fecal egg counts (FEC) during the periparturient rise (PPR), the major source of pasture contamination in spring.

Our specific objectives were to:
1. Determine if ewes with low FECs as lambs have a correspondingly lower PPR as adults;
2. Determine if lambs born to ewes with low PPR have correspondingly lower FECs;
3. Determine if ewes with low FECs as lambs bred to rams with low FECs as lambs produce offspring with correspondingly low FECs.
Ewes typically undergo a temporary weakening in their immunity to parasites during lactation. As a result there is a subsequent increase in eggs being shed on the pasture in manure, as measured by fecal egg counts, and this well recognized phenomenon is called the periparturient rise (PPR) in fecal egg count. This increase is often dramatic and is the major source of the new generation of worm larvae on pasture at the beginning of each grazing season for flocks that lamb in early spring. These large numbers of parasite eggs contaminate the pasture at exactly the time when lambs are most susceptible. In addition, high worm burdens during PPR may adversely affect the ewe through loss of body condition and reduced milk production, forcing lambs to graze at a younger age on highly contaminated pastures. Thus, selection for ewes with lower fecal egg counts during lactation could lower the contamination of pasture and the exposure of young lambs to parasite larvae, while improving growth and leading to greater productivity.

As part of our previous NCR-SARE grant FNC05-583, each farm was able to identify and select ewe lambs with low FEC as lambs. In this project we monitored those ewes to see how they responded to the PPR as one and two year old ewes. We analyzed and compared the FECs of these ewes during lactation to both their own FECs as lambs, and the FECs of their offspring. In fall 2007 and 2008, some of these low FEC ewes were mated with rams that had shown low FEC as lambs. We compared the offspring of those matings to the offspring of other pairings of animals with known higher FECs to learn more about the accuracy of predicting parasite resistance.

Data from the Bielek farm over several years showed a typical pattern of FECs during lactation (PPR) as a low FEC prior to lambing with counts reaching a peak four to six weeks after lambing, and returning to a low or lower count eight to ten weeks post lambing. Based on this observation, fecal samples were collected on all ewes at lambing; four to six weeks post lambing (the anticipated time of peak PPR); and eight to ten weeks post lambing to determine if FECs had dropped. To ensure consistency, all FECs were performed by the veterinary parasitology laboratory at either Virginia Tech (Year 1) or Louisiana State University (Year 2). Body condition and FAMACHA scores were recorded on each ewe at regular intervals through lactation. Ewes were selectively dewormed as needed, and the information recorded. To monitor ewe productivity, weights of as many lambs as possible were collected at birth, 30 and 60days.

All lambs were monitored every one to two weeks with FAMACHA, body condition and vigor scoring starting when the lambs were expected to start being exposed to parasites on pasture, usually at 6-8 weeks of age. The exact age varied by farm and by year depending on time of lambing and weather conditions. A group average FEC of at least 750 epg (eggs per gram) is necessary to ensure a sufficient parasite challenge to identify animals above or below the group average FEC. A parasite challenge was determined to exist when either 10% of the lambs had a FAMACHA score of 3 or higher, or a composite FEC consisting of fecal samples from 10-15 lambs reached at least 750 epg, Once a parasite challenge was confirmed, an individual FEC was collected on all lambs at that time and again at 21-28 day intervals for an additional one to two collections. A final FEC was collected each year on the Bielek and Stoneback farms in early October. FAMACHA scores were also recorded at each collection date. Sire ID, age of dam, sex, type of birth and rearing were collected on each lamb and maintained in a database.

Conversations with other producers and researchers suggested the increased scouring (diarrhea) in lambs often seen late in the season (August/September) might be due to a change in the parasite species population over the course of the summer. To test this idea, we submitted fecal samples for larval culture to LSU in the spring. A DrenchRite assay was performed by the University of Georgia in August to not only identify parasite species at that time of year, but to identify the level of anthelmintic resistance in each flock.

All data was 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, Dr. Charles Parker and Dr. David Notter.

PEOPLE
William P. Shulaw, DVM, MS, and Charles Parker, PhD, have been involved with this project from the beginning, and David Notter, PhD became involved in our previous grant. 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. Notter directs the National Sheep Improvement Program Genetic Evaluation Center at Virginia Tech. Drs. Shulaw, Parker and Notter helped develop the monitoring plan, provided input in analyzing the results, and provided advice, support and encouragement. Data from this project has been submitted to Dr. Notter to be included in his National Sheep Improvement Association (NSIP) fecal egg count EPD (expected progeny difference) project. We will work with Dr. Notter to correlate our on-farm observations with his NSIP FEC EPDs.

Dr. Steve Loerch and Gary Lowe from the Ohio State University Department of Animal Science generously donated their time to perform an initial correlation analysis of our data.

RESULTS
Correlation analysis of the data was done by Gary Lowe in the OSU Animal Science Department. He used SAS, a statistical analysis program, for the data analysis. He first looked at the raw data. Because of the large variability between FECs and the changes seen from farm to farm and throughout the grazing season, he calculated the ratio of each animal’s FEC to the average FEC of their contemporary group for that sampling date. In addition, he performed a log conversion of the FEC to statistically smooth out the high animal-to-animal variability typically seen in FECs. The data set regarding FECs then included: 1) raw FECs; 2) the ratio of each individual animal FEC to the average FEC of their group on each date; and 3) the log converted FECs. For comparisons and correlations, only log-converted FECs and ratios (using log-converted FECs) were used.

Objective 1:
There was a positive correlation between the FEC at 1st challenge as a lamb and the subsequent FEC of that ewe during the PPR at lambing. A correlation was also seen between a lamb’s October FEC and her average FEC as a ewe during the PPR.

Objective 2:
There were some negative correlations over time between the ewe FEC during the PPR at all points and the ewe’s offspring's FEC at first challenge (pre-weaning). This was seen more on the Bielek farm (a highly selected flock). The one unselected flock had very small numbers of animals. A high positive correlation was seen between the ewe FEC during PPR and her offspring’s weaning and post-weaning FEC.

Objective 3:
Correlation was seen between the average of the sire and dam's FEC at first challenge as lambs and their offspring's FEC at first challenge. This observation supports observations seen in our other projects.

Other observations:
• A strong correlation was seen between the sire’s FEC at 1st challenge as a lamb and his offspring’s FEC at 1st challenge.
• A lamb's 1st challenge FEC seemed to be unassociated with its October FEC as a lamb.
• A ewe's average PPR FEC was related to her dam's average PPR FEC (if the dam was low, the daughter was more likely to be low).
• A ewe's FEC during the PPR was strongly correlated to the FEC at peak lactation (4-6 weeks post lambing).
• There was no correlation seen between a lamb’s FEC through the summer and the 120 day weaning weight EPD, suggesting there was no relationship between growth and parasite resistance.

For the most part, these results are as expected and support work done previously by Dr. David Notter and our previous NCR-SARE results. Two interesting results were the positive correlation between the October FEC as a lamb and the PPR as a ewe, and the positive correlation between a ewe’s FEC during PPR and that of her dam.

DISCUSSION
We found this project to be more challenging than our previous work on identifying parasite resistant sires. The issues appear to be quite complex, and even more than in the sire work, affected by farm-level management factors including grazing management, time of lambing, weather, level of parasite challenge from the pastures, and especially genetics and prior selection for resistance at the farm level. More controlled studies are needed in a research setting.

Our collaborators strongly suggest we continue with a regression analysis of the data to attempt to control for some of the factors mentioned above, and we plan to follow through on that suggestion. This will require the services of a biostatistician. It should be noted that our work was done with small numbers of animals in each flock. This made the intensive amount of work manageable on each farm, but created challenges in analyzing and interpreting the data.

We believe our project was successful and has practical application for other producers. Specifically, our work:
1. supports previous work suggesting that selecting lambs based on their FEC at first challenge (the first time the average FEC of their contemporary group was greater than 750 epg or 10% of the lambs have a FAMACHA score of 3 or higher) allows selecting individuals with early onset of resistance to gastrointestinal worms;
2. suggests that sampling a lamb’s FEC at first challenge can identify animals that are likely to produce offspring with similar FEC at first challenge (either high or low);
3. supports the practice of breeding ewes and rams that both had low FEC as lambs to produce offspring with lower FECs as lambs;
4. suggests that selecting ewe lambs with low FEC in the fall may result in ewes with lower FECs during their PPR at lambing;
5. Daughter-dam comparison correlations for PPR were found to be positive therefore indicating PPR/FEC of ewes to be a heritable trait.

The results of this NCR-SARE project suggest that other producers can use these methods successfully to help reduce their reliance on anthelmintics and select for parasite resistant seedstock. A shepherd could choose to select or purchase replacement lambs with increased resistance to parasites who are able to grow on pasture, and with the ability to pass that trait on to their offspring. Or, they could select or purchase ewes that have lower FECs during the periparturient rise that would shed fewer eggs, thereby lowering the pasture contamination and challenge for their lambs.

If further analysis and/or research confirm the predictive value of the three sampling dates mentioned above, it would require much less work to identify parasite resistant stock. This would allow the producers with the interest and ability to pursue this work to add genetic value to differentiate and market their animals at a higher price. Those producers with less interest or resources could benefit by purchasing parasite resistant animals to meet their individual goals and needs.

OUTREACH
Data and experiences from our previous NCR-SARE grant (FNC05-583) and preliminary data from this project were presented at the annual Katahdin Hair Sheep Expo held in Hagerstown, MD on September 26, 2008.

Data collected during the first year of the project have been shared with our cooperators: Dr. David Notter for use in his work with the NSIP, and Dr. William Shulaw for use in his extension work and FAMACHA training.

Three students on two farms have assisted with handling the sheep, FAMACHA scoring, weighing and fecal collections. Two of the students assisted with data entry and recordkeeping. One of the students had no prior experience with sheep. All became very interested in the project and learned a new aspect of sustainable agriculture and sheep management.

Results have been shared with the Ohio State University Agricultural Technical Institute’s sheep class on February 19, 2009 and February 24, 2010. Preliminary results were also included as part of a presentation at the Ohio Ecological Food and Farming Association (OEFFA) annual conference on February 22, 2009.

A summary of the 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, and an article will be submitted to the Shepherd magazine. The information will be shared through presentations at the KHSI and OEFFA annual meetings.