Utility of the carbohydrate larval antigen (CarLA®) saliva test to lower the risk of gastrointestinal parasitism in Ontario sheep flocks

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Gastrointestinal parasitism in sheep is a significant constraint to production on pasture and requires a multi-faceted approach for long-term sustainable control; one such approach is to select sheep that are better able to immunologically manage parasite infection (i.e. genetic resistance). One potential tool for this approach is to use The CarLA Saliva Test (AgResearch, New Zealand), which measures antibodies produced by sheep to the infective stage of parasites on pasture. In recent work carried out by researchers at the University of Guelph on one sheep flock in southern Ontario, ewe lambs with medium-to-high CarLA levels (MH-CarLA) had lower parasite fecal egg counts (FEC) than sheep with low CarLA levels. This project will expand this work by evaluating the utility of The CarLA Saliva Test in a number of flocks and breeds. By following replacement ewes over two grazing seasons, it will determine if MH-CarLA ewe lambs, by comparison to those with lower CarLA levels, have lower parasite levels, and are more likely to give birth to offspring with higher CarLA levels, better growth characteristics and lower FEC in their first grazing season. The data obtained by this project will help evaluate the performance of The CarLA Saliva Test under Ontario grazing conditions. In additional work, economic analyses will be carried out to estimate the economic benefit associated with using the test to manage parasites on Canadian farms. Collectively, the findings will facilitate transfer of the test from New Zealand to a diagnostic laboratory in Ontario so that it can potentially be offered to sheep producers across Canada. Collaborators on this project are the Canadian Sheep Breeders' Association, Ontario Sheep Farmers, and the Ontario Ministry of Agriculture, Food and Rural Affairs.