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/g ain). Design-Longitudinal observational study. Animals-34 weaned mixed-breed beef steers. Procedure-Serologic status for N caninum was determined for each steer on d ays 0 (weaning), 88, 116, 144, 172, and 200, using an agglutination test. I ndividual 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 imm ediately following serum sample collection. A mixed mode, using repeated-me asures with an unstructured covariance matrix, was used in the analysis. Br eed, age, and pen effects were controlled for in the analysis. Results-A reduction in average daily gain for the period following a positi ve serologic result was detected for the entire trial (6 measurements/steer ). This may have been attributed to a significant impairment in feed effici ency rather than to an impairment in feed intake. Changes in serologic stat us 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 wei ght gain and feed efficiency were associated with the presence of antibodie s against N caninum in postweaning beef steers.