Leptospirosis seroprevalence in Canadian beef calves at or near fall weaning

Our objective was to estimate the seroprevalences of 6 Leptospira serovars in beef calves at or near fall weaning and assess how concentrations of serovar antibody titers in weaning-age calves varied with Leptospira herd vaccination programs.

Serum was collected from 1922 beef calves from 106 herds in the Canadian Cow-Calf Surveillance Network (C3SN).

A microscopic agglutination test was used to measure antibody titers for serovars Bratislava, Canicola, Grippotyphosa, Hardjo, Icterohaemorrhagiae, and Pomona. Records of Leptospira vaccine use were available for cows and nursing calves from 94 herds. Generalized estimating equations were used to estimate the associations between serovar antibody titers in weaning-age calves and the number of doses of Leptospira vaccine administered to cows.

Overall, 90.8% of sampled calves had undetectable (< 50) antibody titers to all tested serovars, whereas 3.2% of sampled calves from 26.4% of participating herds had a positive (≥ 100) titer to 1 or more serovars. The seroprevalences at both the calf and herd levels were higher for the host-adapted serovar Hardjo in western Canada and higher for the non-host-adapted serovars in eastern Canada. The probability of calf serovar Icterohaemorrhagiae titer increasing by 1 doubling dilution was 3.6× (95% CI: 1.7, 7.7) higher in herds that administered 2 doses of Leptospira vaccine to cows compared to herds that did not vaccinate against this pathogen.

Based on the serological evidence, few weaning-age beef calves across Canada have been exposed to pathogenic Leptospira bacteria.