COLOSTRUM FROM DAMS LIVING IN A HEARTWATER ENDEMIC AREA INFLUENCES CALFHOOD IMMUNITY TO COWDRIA-RUMINANTIUM

Two studies were carried out to determine whether colostrum from dams living in a heartwater-endemic area has an influence on calfhood immun ity to Cowdria ruminantium infection. The initial study was conducted using Friesian calves originating from a heartwater-free herd. Experim ental groups consisted of calves receiving colostrum from dams living in a heartwater-endemic area and known to be exposed to C. ruminantium (as determined by the indirect fluorescent antibody test) and calves receiving colostrum from dams located in a heartwater-free area. All c alves were challenged at 3 days of age with a homologous C. ruminantiu m blood stabilate originating from the same area as the endemic colost rum. A significant difference in both the intensity of clinical reacti ons and percentage of fatal heartwater cases was noted between the two groups of calves. Three of the five calves receiving the colostrum fr ee of C. ruminantium-specific antibodies succumbed to challenge, where as none of the five calves receiving the colostrum from the heartwater -endemic area showed any clinical reactions. A second similar study wa s carried out using 12 mixed breed calves born in a heartwater-endemic area of Zimbabwe. The results from this study supported the findings of the first. The significant role of colostrum in calfhood immunity t o C. ruminantium infection is discussed in relation to the epidemiolog y and control of heartwater.