Type C botulism in turkeys: determination of the median toxic dose.

The median toxic dose (TD50) of type C botulinum in turkeys was determined using an up-and-down method for toxicologic testing. Birds were dosed intravenously with 10, 20, or 40 mouse lethal dose per kilogram body weight (MLD/kg) of type C botulism toxin and observed for 5 days. Administration of toxin resulted in acute death, posterior paresis, or no effect, depending upon the dose. The TD50 causing posterior paresis was calculated as 25.75 MLD/kg (confidence interval = 17.08-38.82 MLD/kg). Posterior paresis was identified as the principal sign associated with sublethal botulism toxicosis in turkeys. The resultant posterior paresis was similar to the clinical syndrome observed in an unsolved field investigation.