Association of serologic status for Neospora caninum and postweaning feed efficiency in beef steers

Objective-To determine the effects of serologic status for Neospora caninum on short-term weight gain, feed intake, and feed efficiency (feed intake/gain). Design-Longitudinal observational study. Animals-34 weaned mixed-breed beef steers. Procedure-Serologic status for N caninum was determined for each steer on days 0 (weaning), 88, 116, 144, 172, and 200, using an agglutination test. Individual steer body weight was measured on days 0, 88, 116, 144, 172, 200, and 242 (slaughter). Daily feed intake was monitored from days 116 through 242. Serologic status was matched to animal performance for the period immediately following serum sample collection. A mixed mode, using repeated-measures with an unstructured covariance matrix, was used in the analysis. Breed, age, and pen effects were controlled for in the analysis. Results-A reduction in average daily gain for the period following a positive serologic result was detected for the entire trial (6 measurements/steer). This may have been attributed to a significant impairment in feed efficiency rather than to an impairment in feed intake. Changes in serologic status in individual steers over time were common; additionally, the effects of serologic status on steer performance were also transitory. Conclusions and Clinical Relevance-Significant reductions in short-term weight gain and feed efficiency were associated with the presence of antibodies against N caninum in postweaning beef steers.