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Immune response may combat parasites in sheep

Researchers at the University of Guelph’s Ontario Veterinary College (OVC) are investigating ways to identify Ontario sheep able to better develop immunity to gastrointestinal parasites.

Gastrointestinal parasites can be deadly for sheep, in particular Haemonchus contortus, impacting sheep health and productivity. Widespread resistance of these parasites to the most common anthelmintics (dewormers) makes managing these parasites even more difficult.

Identifying and selecting sheep Field visit teams assess sheep on the research project.breeding stock that can more rapidly and effectively develop immunity to these parasites could be an important part of any parasite control program and reduce dependence on anthelmintic drugs.

OVC graduate student Emma Borkowski is working with OVC professors Andrew Peregrine, Department of Pathobiology, and Paula Menzies, Department of Population Medicine, as well as Ontario Agricultural College professor Dr. Niel Karrow, Department of Animal Biosciences, to investigate how sheep pastured under Ontario’s climate develop immunity to parasites.

Researchers hope to determine how sheep develop immunity to these parasites

By characterising a number of different immune parameters, and determining how sheep develop immunity to these parasites, they hope to provide tools that will help producers select animals better able to mount an immune response.  This will assist producers in their parasite management programs and will reduce dependence on anthelmintic drugs to treat sheep with heavy infections.

The project is following over 100 ewe lambs on an Ontario farm over two grazing seasons, which includes lambing and rearing their first litter of lambs. In addition, lambs from the University of Guelph’s Ponsonby research flock, selected for their stress response or for their cellular and antibody immune response, are being co-grazed with this flock from April to November in each of those two years.

Researchers will track clinical parameters indicative of parasite levels in the lambs to evaluate how they mount an immune response to parasite exposure. Assessments will include looking at body condition, FAMACHA© score as a clinical indication of anemia, hematology to check the lambs’ total protein, dag scores for an indication of diarrhea, as well as following the sheep’s immune response through a direct measure of parasite-specific antibody level in their saliva and an indirect measure, fecal parasite egg counts.

 “In New Zealand, where there is a larger sheep industry, they have been looking at parasitism for longer and have determined that immunity to parasites is a moderately heritable trait in those animals,” says Borkowski.  “However, they have a more temperate climate, very different from here.  Furthermore, in Canada, we pasture for only half of the year because of our cold, harsh winters.  We believe this affects how sheep develop and maintain immunity to parasites.  At this point we can’t say exactly how much this makes things different from New Zealand but we hope to learn this from our project.”

We’re trying to figure out if parasite exposure on Ontario pasture is enough for lambs to mount an effective immune response,” she adds.

Important to study immune response in Ontario’s climate

For years, researchers and sheep producers have been looking for a reliable method to identify sheep that are better at managing internal parasite infections.  Some breeds have this trait, most commonly tropical breeds, but they are not able to withstand our Canadian climate.  However, within Canadian breeds there are individuals that have lower parasite egg counts, suggesting that these animals have an ability superior to their flock-mates.  “We hope to identify what this ability is by investigating their immune response,” says Borkowski. “It’s important to see how this response works with an average flock in Ontario’s climate.”

“We believe that screening replacement ewes for their immune response is an effective way to improve selection for parasite resistance in sheep and to reduce anthelmintic use on farms”, she adds.

“Anthelmintics will always be important for managing clinical disease in parasitized animals but we need to emphasize the use of alternative strategies to try to prevent clinical disease from happening and to try to prevent anthelmintic resistance from developing when we do have to use these drugs.   Identifying those sheep with a superior ability to immunologically manage infections, and using them in a breeding program to pass on this trait to their offspring, is one of those alternative strategies that has shown a lot of promise elsewhere,” she adds.

The research is funded by the Canadian Agricultural Adaptation Program, the Ontario Ministry of Agriculture, Food and Rural Affairs, and the Ontario Sheep Marketing Agency.