Bovine brucellosis in the Highveld region: incidence in dairy herds.

Bulk tank milk samples which were collected twice with an interval of 2 months from 2103 herds were tested for brucellosis by employing the brucella ring test. Farmers involved were all supplying industrial milk to the National Co-operative Dairies. A questionnaire was circulated to these farmers in which they were asked to indicate how heifer calf vaccination with strain 19 vaccine was practised on their properties. Of the herds tested, 18.1% could be regarded as infected. This figure varied from 8.9% in the Potchefstroom area to 30.9% in the northern districts of the Hoopstad area. An important cause of this rate of infection should be sought in improper calfhood vaccination. At least 9% of the respondents did not practice heifer calf vaccination whilst another 8.1% only commenced with vaccination during 1985 or later. About 12.4% of farmers commenced heifer calf vaccination prior to 1970.