Mastitis in 85 of 140 dry cows and 16 of 101 milking animals on one farm was shown to be caused by Mycoplasma californicum. The infection was eradicated from the herd over a five month period by a combined programme of identification, segregation and culling of infected animals. Some dry cows produced a self-cure, but the majority calved with nonfunctional quarters which produced very little colostrum and resulted in a high incidence of calf mortality. The source of the infection could not be established, but it was probably spread in the dry cows by the unhygienic application of long acting intramammary antibiotic therapy.
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