An outbreak of Mycoplasma sp. bovine group 7 infection occurred in three large centrally managed dairies. The clinical syndromes included mastitis, abortion and polyarthritis. Mastitis as a result of Mycoplasma sp. bovine group 7 infection was implicated in the spread of infection.
The three dairies involved in the outbreak were centrally managed and located near Sydney, New South Wales. Farms 1, 2 and 3 contained 1050, 1100 and 850 Friesian cows, respectively. Calf rearing practices on the three farms were similar. At 3 days of age calves from farm 2 and 3 were transported to the central calf rearing unit, where usually about 240 calves were housed in individual pens. They were fed with mastitic milk and a commercial milk replacer. Calves were kept in the rearing facility for 4 to 6 weeks before being moved to a clean paddock.
Shortly after the routine mastitis treatment changed on these properties from Mastalone (tetracycline based product) to Orbenin (contains clixacillin), 30% of calves developed severe polyarthritis between 2 and 3 weeks of age. About 150 calves died or were euthanased during the outbreak. At the same time multiple abortions occurred on the three farms and some of these were submitted for laboratory investigation. Routine bacterial culture were unrewarding but Mycoplasma sp bovine group 7 was recovered from the fibrinopurulent synovial exudates of four 14 day old calves, from the stomach contents and lungs of two aborted foetuses and from 5 bulk milk samples when special mycoplasma culture was conducted. The organism was also recovered from individual quarters of the udder from cows.
Mycoplasma sp bovine group 7 caused significant economic losses as a result of mastitis, polyarthritis and abortion. Since mycoplasmas are not susceptable to penicillin based products the infection probably originated from udder infection with the spread of the disease being enhanced by decreased use of tetracycline in the treatment of mastitis. Neonatal calves most likely were infected by the consumption of milk contaminated with the organism. Abortions presumably resulted from mycoplasmaemia during pregnancy. In the absence of specific mycoplasma culture, diseases caused by mycoplasmas may often be missed. This appears to be the first report in Australia of bovine abortions resulting from Mycoplasma sp infection.