Gastrointestinal nematodes in Quebec dairy cattle

Herd prevalence, level of infection estimated by bulk tank milk ELISA testing and related risk factors

Abstract

A cross-sectional observational study was undertaken in Qubec dairy herds to evaluate regional and provincial prevalences of herds with gastrointestinal nematode (GIN) infections in lactating cows, and to determine risk factors associated with level of herd infection. The 5 most recently calved first-lactation cows from each of 208 randomly selected farms in 7 pre-defined regions of Qubec were sampled for faeces collection in July to August 1995. On the same occasion, a bulk tank milk sample was collected. A questionnaire on replacement and grazing practices was filled out for each farm. Faecal samples were examined and faecal egg counts were determined for trichostrongylids, Capillaria, Nematodirus, Trichuris, Strongyloides, and total GIN eggs. Weighted provincial estimates for prevalence of herds with positive coprologies to these parasites ranged from 4 to 93%. Median faecal egg count per herd was low (17 eggs per 5 g of faeces). Milk samples were submitted for an indirect ELISA test to detect antibodies against Ostertagia and Cooperia. Level of herd infection, as estimated by Ostertagia and Cooperia bulk tank milk ELISA titres (BTTs), varied (P<0.05) among regions. Questionnaire-derived risk factors most significantly associated with an increased bulk tank Ostertagia titre were exposure of lactating cows to pasture, intensive grazing of heifers on farm, contamination history of heifers' pasture, and incomplete pasture rotation for heifers. Very high stocking rates for cows and heifers and mechanical mowing during the grazing season of heifer pastures were associated with decreased ELISA titres. The results of this study indicate that the prevalence of nematode infections in first-lactation cows is very high in Qubec herds, with trichostrongylid infections being the most frequently observed. The association between bulk tank milk ELISA titres for Ostertagia and herd-level management practices capable of having an impact on exposure of cows to parasites suggest that BTTs could be a valuable indicator of herd infection level. Proper knowledge of regional prevalences, differences among mean regional titres, and the association between titres and of herd-level risk factors can help veterinarians with their decisions regarding parasite prevention and treatment.