HERD PREVALENCE AND GEOGRAPHIC-DISTRIBUTION OF, AND RISK-FACTORS FOR,BOVINE PARATUBERCULOSIS IN WISCONSIN

A random sample of Wisconsin daily herds, stratified by herd size, wer e tested for paratuberculosis by use of an absorbed ELISA procedure. T he ELISA was optimized for overall accuracy by means of receiver opera ting characteristic curve analysis, and had a sensitivity and specific ity of 50.9 and 94.9%, respectively. Herd prevalence was analyzed for correlation with responses to a management practices questionnaire com pleted by the herd owners. One hundred and fifty-eight herds and 4,990 cattle were tested. Of these, 50% of herds and 7.29% of cattle had po sitive test results. Calculation of true prevalence from the apparent prevalence indicated that 4.79% of cattle and 34% of the Wisconsin dai ry herds tested had serologic evidence of paratuberculosis. Among the 54 herds classified as positive on the basis of true prevalence estima tion, the mean number of test positive cattle was 20.3% The geographic distribution of herds with positive results was not uniform. More inf ected herds were found in the southern and western districts of Wiscon sin than in the eastern district. The west-central district had a larg er number of infected herds than did other districts. By use of chi(2) analysis, the only management factor found to be significantly associ ated with herd prevalence was housing of carves after weaning (P = 0.0 3). Specifically, in herds with higher prevalence, calves were separat ed after weaning into calf barns and hutches rather than into pens in the cow barn more often than in herds with lower prevalence. This fact or was also considered significant by use of logistic regression analy sis. Logistic regression analysis also revealed that herd size and loc ation of farm by district of the state were significantly related to h erd paratuberculosis prevalence.