Objective—To determine the seroprevalence for
Neospora caninum in a population of beef calves in a
feedlot and the association of serologic status with
postweaning weight gain and carcass measurements.
Design—Longitudinal observational study.
Animals—1,009 weaned beef steers from 92 herds.
Procedure—Samples were obtained from all steers
at time of arrival at a feedlot. Serologic status for
Neospora spp was determined, using an agglutination
test. Results of serologic testing were compared with
calf growth and carcass data, using multivariate
regression with generalized estimating equations.
Results—Of 1,009 calves, 131 (12.98%) were
seropositive, and 54 of 92 (58.7%) consignments had
≥ 1 seropositive calf. Median within-consignment
prevalence for consignments in which there was ≥ 1
seropositive calf was 20%. Seropositive status was
associated with significant reductions in average daily
gain, live body weight at slaughter, and hot carcass
weight and an increase in ribeye area-to-hot carcass
weight ratio. Seropositive status also was associated
with significant increases in cost of treatment and significant
reductions in income. Sick seropositive calves
had the highest cost of treatment. An economic loss
of $15.62/calf was projected for seropositive calves.
Conclusions and Clinical Relevance—Significant
reductions in postweaning weight gain, carcass
weight, and economic return were associated with
detection of antibodies to N caninum in beef calves
in a feedlot. (J Am Vet Med Assoc 2000;217: