After an outbreak of mastitis in cattle caused by Mycoplasma bovis a study was made in 5 herds with recent cases (principal herds) and in 4 control herds. In the principal herds, M . bovis was isolated from milk samples, nasal swabs, and from one vaginal swab. M . bovis was also isolated from nasal swabs of calves in 2 of the 4 control herds, whereas all milk samples and vaginal swabs from the control herds were negative.Evaluation of serum antibody titres to M . bovis among non-mastitic animals of 3 principal herds and 1 control herd showed no difference in distribution of the titre values, which generally were low. However, cows excreting M . bovis in the milk had high antibody titres. The way of introduction to the herds and the spread of the infection within the herds could not be established by the study, which was supplemented by a DNA restriction fragment analysis of a number of M . bovis isolates.
IntroductionMycoplasma bowis infection in cattle was diagnosed for the first time in Denmark in November 1981. M . bowis was isolated from pneumonic lesions in a calf (FRIIS, 1984) and since then, it has been found sporadically in pneumonic calf lungs.The first cases of mastitis in Denmark caused by M . bowis were diagnosed in the spring of 1984. About 100 cows from 14 herds within a small geographic area were affected, Apart from a few sporadic cases, later outbreaks were also clustered within restricted geographic areas.Until now, M. bowis is the only mycoplasma species found as a cause of mastitis in Denmark. In order to study the epidemiological aspects of the infection, a field study of the most recent outbreaks was carried out. The aims were: 1 . To examine the occurrence of M . bowis in herds with and without diagnosed M . bowis mastitis, 2. To study how M. bowis was introduced into the herds, and 3. How M . bowis had spread within the infected herds. Starting in January, 1986, M . bovis mastitis had been diagnosed in 57 cows from 16 different herds in the same district. In cooperation with the local practising veterinarians, 5 herds with recent cases of M . bovis mastitis (principal herds) were selected for the study. Four control herds from the same area, without diagnosed cases of M . bovis mastitis, but comparable to the M . bovis mastitis herds concerning housing, supplementation, and management, were chosen as control herds. U.S. C o p y q h t Clearance Cenrer Code Statement: 0931 -1793/91/3803 -0195$02.50/0
Material and Methods