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:
Objective—To determine the epidemiologic plausibility
of a sylvatic transmission cycle for Neospora caninum
between wild canids and beef cattle.
Design—Spatial analysis study.
Animals—1,009 weaned beef steers from 94 beef
herds in Texas.
Procedure—Calves were grouped on the basis of
seroprevalence for N caninum and ecologic region in
Texas. The Morans I test was used to evaluate spatial
interdependence for adjusted seroprevalence by ecologic
region. Cattle density (Number of cattle/259 km2
[Number of cattle/100 mile2] of each ecologic region)
and abundance indices for gray foxes and coyotes
(Number of animals/161 spotlight-transect [census] km
[Number of animals/100 census miles] of each ecologic
region) were used as covariates in spatial regression
models, with adjusted seroprevalence as the outcome
variable. A geographic information system (GIS) that
used similar covariate information for each county was
used to validate spatial regression models.
Results—Spatial interdependence was not detected
for ecologic regions. Three spatial regression models
were tested. Each model contained a variable for cattle
density for the ecologic regions. Results for the 3
models revealed that seroprevalence was associated
with cattle density and abundances of gray foxes, coyotes,
or both. Abundances of gray foxes and coyotes
were collinear. Results of a GIS-generated model validated
these spatial models.
Conclusions and Clinical Relevance—In Texas, beef
cattle are at increased risk of exposure to N caninum
as a result of the abundance of wild canids and the
density of beef cattle. It is plausible that a sylvatic
transmission cycle for neosporosis exists. (J Am Vet
Med Assoc 2000;217:1361–1365)