Evidence of point-source exposure to Neospora caninum and protective immunity in a herd of beef cows

Objective-To determine whether cows with evidence of previous infection wit h Neospora caninum were less likely to abort or give birth prematurely duri ng an outbreak of neosporosis, compared with herd-mates with evidence of pr imary infection. Design-Cohort study. Animals-208 pregnant beef cows. Procedures-Aborted fetuses and calves born prematurely were examined during an outbreak of neosporosis in a herd of beef cows. Sera were collected fro m all cows during the outbreak and again 71 days later. Cows were classifie d into groups on the basis of normal and abnormal reproductive outcomes. Se ra were examined, using an avidity ELISA procedure for N caninum, and resul ts were compared between groups and among time points. Results-Antibody concentrations decreased significantly and IgG avidity val ues increased significantly over time. During the outbreak, cows with norma l reproductive outcomes were significantly more likely to have high IgG avi dity values than cows with abnormal reproductive outcomes. Conclusions and Clinical Relevance-The herd had numerous abortions and prem ature births with evidence of recent point-source exposure to N caninum. Th erefore, to reduce risk of transmission of N caninum to cattle, attempts sh ould be made to prevent canine feces from contaminating feed, especially fe edstuffs used to prepare mixed rations for cattle. Cows with evidence of pr evious exposure to N caninum were less likely to abort or give birth premat urely during the outbreak than cows with primary infections with N caninum; this finding suggests development of protective immunity in previously inf ected cows.