A Probable source of Neospora caninum infection in an abortion outbreak in dairy cows

A small dairy had an outbreak of neosporosis. One-third of pregnant cows aborted or gave birth to a weak, premature calf over a period of 11 weeks. Serologic results of a Neospora caninum avidity enzyme-linked immunosorbent assay (ELISA) test were indicative of widespread, recently acquired infections in the cows and also in the farm dog. This dog was accustomed to sleeping and defecating in a pile of chopped hay used in the total mixed dairy ration, so it was a possible vector of infection in this outbreak. Replacement heifers, which did not consume the mixed ration or the chopped hay, had a low seroprevalence to N. caninum and did not have abortions. A new isolate of N. caninum, designated NC-Illinois, was obtained from a premature calf. The circumstances at this dairy illustrate a specific management factor that could help prevent outbreaks of neosporosis. To reduce the risk of infecting cattle with N. caninum, dogs and coyotes, which are definitive hosts of this parasite, should be prevented from defecating in stored feedstuffs. The small dairy in this study might have prevented the outbreak by simply keeping the door to the hay room closed. Large dairies could prevent contamination of stored feedstuffs by erecting a chain-link fence with automatic gates around the area where piles of silage and commodities are kept.