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 immunity to Cowdria ruminantium infection. The initial study was conducted using Friesian calves originating from a heartwater-free herd. Experimental 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 calves were challenged at 3 days of age with a homologous C. ruminantium blood stabilate originating from the same area as the endemic colostrum. A significant difference in both the intensity of clinical reactions and percentage of fatal heartwater cases was noted between the two groups of calves. Three of the five calves receiving the colostrum free of C. ruminantium-specific antibodies succumbed to challenge, whereas none of the five calves receiving the colostrum from the heartwater-endemic area showed any clinical reactions. A second similar study was 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 to C. ruminantium infection is discussed in relation to the epidemiology and control of heartwater.