Field studies on the efficacy of a long acting preparation of oxytetracycline in controlling outbreaks of enzootic abortion of sheep

The effects of long acting oxytetracycline in controlling outbreaks of enzootic abortion of ewes were studied over three consecutive years in 13 different commercial flocks. When used in the face of an outbreak the compound produced a statistically significant reduction in abortion in treated ewes when compared to untreated controls. There was, however, only a marginal difference in the overall abortion rate between treated and untreated groups of ewes in known infected flocks, where the drug was used in anticipation of an abortion storm, mainly because the abortion rate was too low in the control group. It is suggested that oxytetracycline therapy should only be used in an effort to control an actual abortion outbreak on the understanding that the treatment will not eradicate infection from the flock.