Association of serologic status for Neospora caninum with postweaning weight gain and carcass measurements in beef calves

Objective-To determine the seroprevalence for Neospora caninum in a populat ion of beef calves in a feedlot and the association of serologic status wit h postweaning weight gain and carcass measurement. 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 fee dlot. Serologic status for Neospora spp was determined, using an agglutinat ion test. Results of serologic testing were compared with I calf growth and carcass data, using multivariate regression with generalized estimating eq uations. Results-Of 1,009 carves, 131 (12.98%) were seropositive, and 54 of 92 (58.7 %) consignments had greater than or equal to 1 seropositive calf. Median wi thin-consignment prevalence for consignments in which there was greater tha n or equal to 1 seropositive calf was 20%. Seropositive status was associat ed with significant reductions in average daily gain, live body weight at s laughter, and hot carcass weight and an increase in ribeye area-to-hot carc ass weight ratio. Seropositive status also was associated with significant increases in cost of treatment and significant reductions in income. Sick s eropositive 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 we ight gain, carcass weight, and economic return were associated with detecti on of antibodies to N caninum in beef calves ina feedlot.