Neospora caninum serostatus and culling of Holstein cattle

Gerard Cramer Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

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David Kelton Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

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 DVM, PhD
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Todd F. Duffield Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

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Jamie C. Hobson Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

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Kerry Lissemore Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

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Sharon K. Hietala California Animal Health and Food Safety Laboratory System, University of California, Davis, CA 95616.

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Andrew S. Peregrine Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

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 BVMS, PhD, DVM

Abstract

Objective—To determine whether time until culling or risk of culling was associated with Neospora caninum serostatus among Holstein cattle in dairy herds in Ontario.

Design—Retrospective cohort study.

Animals—3,412 cows in 56 herds.

Procedure—Blood samples were collected, and serum was tested for antibodies against N caninum. Information on cows that were culled was collected during the 1- to 2-year period that producers were unaware of serostatus of individual cows in their herds.

Results—Herd prevalence of N caninum-seropositive cows ranged from 0 to 68.3% (median, 7.0%). During the time of the study, 184 of 359 (51.3%) N caninum-seropositive cows were culled, compared with 1,388 of 3,053 (45.5%) seronegative cows. Mean time from blood sample collection to culling for seronegative cows (289 days; 95% confidence interval, 280 to 299 days) was not significantly different from mean time for seropositive cows (296 days; 95% confidence interval, 269 to 323 days). Survival analysis indicated that N caninum serostatus was not associated with time to culling or risk of culling.

Conclusions and Clinical Relevance—Results suggest that N caninum serostatus of Holstein cows in Ontario was not significantly associated with either time to culling or risk of culling. Thus, N caninum serostatus alone should not be used to determine whether cows should be culled. (J Am Vet Med Assoc 2002;221:1165–1168)

Abstract

Objective—To determine whether time until culling or risk of culling was associated with Neospora caninum serostatus among Holstein cattle in dairy herds in Ontario.

Design—Retrospective cohort study.

Animals—3,412 cows in 56 herds.

Procedure—Blood samples were collected, and serum was tested for antibodies against N caninum. Information on cows that were culled was collected during the 1- to 2-year period that producers were unaware of serostatus of individual cows in their herds.

Results—Herd prevalence of N caninum-seropositive cows ranged from 0 to 68.3% (median, 7.0%). During the time of the study, 184 of 359 (51.3%) N caninum-seropositive cows were culled, compared with 1,388 of 3,053 (45.5%) seronegative cows. Mean time from blood sample collection to culling for seronegative cows (289 days; 95% confidence interval, 280 to 299 days) was not significantly different from mean time for seropositive cows (296 days; 95% confidence interval, 269 to 323 days). Survival analysis indicated that N caninum serostatus was not associated with time to culling or risk of culling.

Conclusions and Clinical Relevance—Results suggest that N caninum serostatus of Holstein cows in Ontario was not significantly associated with either time to culling or risk of culling. Thus, N caninum serostatus alone should not be used to determine whether cows should be culled. (J Am Vet Med Assoc 2002;221:1165–1168)

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