Identifying ewes resistant to gastrointestinal parasitic worms during gestation and lactation

View the project final report

• 2009 annual report

Commodities

• Animals: sheep

Practices

• Animal Production: parasite control, livestock breeding, preventive practices
• Education and Training: on-farm/ranch research
• Production Systems: holistic management
• Sustainable Communities: sustainability measures

Sheep are an ideal species for small farms, especially those interested in organic or forage based production. However, an alarming increase in resistance of parasites to chemical dewormers has occurred. Long-term sustainability depends on developing alternative parasite control. Selecting sheep with resistance to parasites has the potential to produce animals that are less susceptible to parasites and to diminish the parasite challenge in their environment. If producers can identify sheep that are resistant to nematodes both as a lamb and as a peri-parturient ewe, they will be able to limit infestation of the pastures, reduce mortality and performance losses and reduce their reliance on dewormers. Increasing the resistance of the sheep will also work to prolong the effectiveness of dewormers that have not succumbed to worm resistance. Sheep that are genetically resistant to parasites, will also remove the major barrier to producing organic lamb meat in warm, moist climates and increase environmental and financial sustainability. Producers and USDA, ARS (Booneville, AR) scientist will be responsible for managing a group of Katahdin sheep enlisted in NSIP. The producers were selected based on past work on the fecal egg counts (FEC) to identify heritable parasite resistance in the lamb and the genetics of their flocks (Bielek, NCR SARE grants FNC 04-523, FNC05-583; Morgan, Newton & Bielek, Katahdin Breed work with the NSIP, D. Notter). A key component of the research is to have ewes sired by common rams and lambs sired by common rams. These producers have shared genetics. At least 25 ewes per farm will be used, including Round Mountain Farm, Hound River Farm, Misty Oaks Farm, and a larger population of ewes from the ARS farm to help increase numbers for validation and statistical analyses.

1. Objective 1) Measure worm FEC of ewes during late gestation and lactation. Fecal samples will be collected directly from rectum from ewes every 14 days, starting approximately two weeks before lambing is due to begin until approximately four weeks after a ewe has lambed (only samples that approximate Days -14, 0, 14, and 28, where Day 0 = day of lambing, will be used for FEC analysis). A pooled fecal sample from several ewes will be cultured to determine population of gastrointestinal nematodes. Flocks without a predominant Haemonchus contortus worm species may not be included in data analyses. However, it is expected that H. contortus will be predominant worm. Cultures will be conducted at ARS, Booneville and FEC will be determined at Louisiana State University (Dr. James Miller’s lab; Drs. Burke and Miller have an extensive collaborative history) using a modified McMaster’s technique. Objective 2) Measure FEC of offspring at first significant exposure to worm parasites. Fecal samples will be collected from lambs for FEC as described above at approximately 60, 90, and 120 days of age. Offspring from ewes described above will be used. A pooled fecal sample from lambs will be cultured to determine population of nematodes. Objective 3) Examine genetic resistance of ewes during the peri-parturient rise with that of their offspring. Genetic analyses will be conducted to determine whether resistance to parasitic worms in the lactating ewe is heritable and correlated with resistance to nematodes as lambs. Correlations will be determined between FEC from each time point from ewe and offspring. A regression analysis will be conducted between ewe FEC and offspring FEC (FEC will be log transformed).