Using salivary anti-CarLA IgA as a tool to manage gastrointestinal parasitism in Canadian pastured sheep *

<p dir="ltr">Identifying sheep with superior immunity to gastrointestinal nematodes (GIN) is of great interest for Canadian sheep producers. Measuring the concentration of salivary immunoglobulin A (IgA) against carbohydrate larval antigen (CarLA) found on all third-stage GIN larvae has shown promise in New Zealand sheep, where salivary anti-CarLA IgA exceeding 1.0 U/ml has been associated with 20–30 % lower fecal egg counts (FEC). However, it remains unclear whether these findings translate to other sheep-producing regions, especially northern climates where GIN epidemiology and flock management differ greatly from New Zealand. Accordingly, this study investigated salivary anti-CarLA IgA testing in sheep under Canadian conditions, and was approved by the University of Guelph Animal Care Committee (#4762). In 2022, an average of 25 ewe lambs per farm were randomly selected on 18 farms in Ontario, Canada, after grazing pasture for a minimum of 60 consecutive days. Body condition, fecal consistency, FAMACHA© score, liveweight, hematocrit, FEC, and salivary anti-CarLA IgA concentration were recorded for each study animal after the grazing season. Study animals returned to pasture in 2023 and were re-sampled 4 weeks after turnout. Multivariable linear regression demonstrated that the salivary anti-CarLA IgA response in 2022 predicted the salivary anti-CarLA IgA response in 2023 (β = 0.213; p < 0.001). In addition, salivary anti-CarLA IgA in 2022 was negatively associated with FEC in 2023 (β = - 0.167; p = 0.025). These data indicate that salivary anti-CarLA IgA measurements appear to be helpful for identifying sheep with superior immune responses to GIN in Canada.</p><p dir="ltr">* Title in ESDA Proceedings: Evaluating the use of salivary anti-CarLA IgA testing to reduce gastrointestinal parasitism in Canadian pastured sheep</p>