The Impact of Estimated Breeding Values on Parasite Resistance and Reduced Parasitism in Sheep

Progress report for OS19-124

Project Type: On-Farm Research
Funds awarded in 2019: $15,000.00
Projected End Date: 03/31/2022
Grant Recipient: USDA-ARS
Region: Southern
State: Arkansas
Principal Investigator:
Dr. Joan Burke
USDA, Agricultural Research Service
Expand All

Project Information


Infection with gastrointestinal nematodes threatens economic viability of small ruminant production in the South and is the major health concern due to widespread GIN resistance to dewormers. Parasitic worms are a year-round problem in the South affecting well over 1 million sheep on more than 230,000 small to mid-size farms that raise small ruminants in the U.S. Gastrointestinal worms can cause reduced weight gains, anemia and death of infected animals. Because of the high prevalence of dewormer resistance (worms that are resistant to all available dewormers), alternative tools that aid in control of worms are extremely important, including parasite resistant genetics. The National Sheep Improvement Program provides predictable, economically important genetic evaluation information to the American sheep industry by converting performance records into relevant decision-making tools. By using sheep (or goats) with predictable genetics or performance attributes, including growth, reproductive or maternal traits, and parasite resistance, a superior flock can be built for both breeding stock and commercial flocks (which focus on lamb production). The genetic predictability uses estimated breeding values, which are science-based, industry-tested measures of an individual animal. No data exists on the impact of parasite resistant EBVs in sheep flocks. There is a large variability in the marker for parasite infection, fecal egg counts, within a breed. Within the Katahdin breed, FEC EBVs range from -100 to 769 (-100 is the best EBV for parasite resistance), indicating great potential for genetic selection. A sheep with -50 FEC EBV would be expected to have a FEC 25 percent lower (a 50 percent improvement) than progeny from an individual with 0 percent. If you were to mate a ram with -100 percent to a group of ewes, then you would expect FEC of his lambs to be 50 percent lower than FEC of lambs sired by a ram with 0 percent FEC EBV. Flocks that have selected for parasite resistance have markedly reduced FEC in their flocks and have flock averages of -60 to -70 percent. The need exists to disseminate parasite resistant genetics to seedstock and commercial farms and better understand their contribution to sustainable sheep production. A more resistant flock will be less likely to succumb to losses due to parasites and remain sustainable. The practice of genetic selection of superior animals or those that possess parasite resistance will increase the sustainability of existing flock management and will have particular relevance to organic and pasture-based production. We are collecting data from NSIP flocks to understand the economic benefit of parasite resistant genetics along with superior growth or maternal traits captured by NSIP EBVs and will report their value in terms of farm sales.

Project Objectives:

The objective is to show producers the value of sheep with high resistance by examining farm gate sales of sheep with EBVs generated by NSIP.


Click linked name(s) to expand/collapse or show everyone's info


Materials and methods:

Five farms currently enrolled in NSIP were used. All animal procedures at ARS were approved by the ARS Animal Care and Use Committee, and producers requested to view humane animal handling procedures available from the American Sheep Industry at Katahdin flocks used were the USDA, ARS (AR; >200 lambs/yr), Jim Morgan and Teresa Mauer (AR; 40 lambs/yr), Roxanne and Milledge Newton (GA; 80 lambs/yr), Kathy Bielek (OH; 50 lambs/yr), Lisa Weeks (VA; 80 lambs/yr), and Vince Pope (WI; 100 lambs/yr). All Katahdin flocks used for this project are enrolled in NSIP, use a minimum of two sires during the breeding season, with a minimum of 10 offspring per sire. Lambs are managed (along with ewes preweaning) as a single group on pasture.  Farmers collected fecal samples for fecal egg count (FEC) analyses from lambs around the first threat of worm infection (usually 60 to 90 days of age), and body weights and FAMACHA scores are determined. A second set of samples/data was collected 30 to 60 days later. Data were entered into NSIP by producers.  Fecal samples are collected directly from the rectum (at least 5 g or large pellets) using lubrication in a plastic bag removing all air, labeled and shipped (can be refrigerated for up to one week) wrapped with newspaper with an ice pack to the Louisiana State University parasitology lab. Feces were analyzed for FEC using a modified McMaster's technique, and, when possible, cultured to determine nematode genera to verify whether Haemonchus contortus (barber pole worm) is the predominant infection.

Producers, whose data will not be disclosed to the public, sent an Excel spreadsheet of FEC, FAMACHA scores, body weights, and EBVs from lambs, along with details of markets that lambs entered into (retained as replacements, sold as market lamb, or sold as replacement) and prices to PI. Data will be analyzed using correlation among all variables, regression between sale dollar of lambs and FEC or FEC EBV, and other appropriate statistical models to determine value of FEC EBVs using SAS (version 9.3, Cary, NC). The ARS flock has data recorded from 2004 to present on multiple FEC, deworming treatment based on high FAMACHA score, pedigree data, and EBVs that will be used to determine relationships between parasite resistance EBVs and need for deworming, production, death losses and other pertinent data to develop economic models. An economist from the University of Arkansas collaborates with our Center on agricultural economic issues and will assist with analyses.

Expected outcomes: Expanding producer knowledge on organic and conventional worm control, and additional producer publications of exceptional quality (see links below in Outreach). Adoption of parasite resistance genetics in flocks will reduce the number of farms exiting, and increase the number transitioning to organic production.

Research results and discussion:

Results are pending data analyses which was delayed due to the pandemic.

Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

50 Consultations
3 Curricula, factsheets or educational tools
1 Online trainings
5 Published press articles, newsletters
1 Webinars / talks / presentations

Participation Summary:

50 Farmers
10 Ag professionals participated
Education/outreach description:

Numerous producers were educated by PI through phone calls, emails, and formal education is pending analyses and ending of pandemic restrictions (PI is not authorized to travel before October 2021).

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation

Project Outcomes

Project outcomes:

Pending analyses and outreach.

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.