Pasteurization of discard mycoplasma mastitic milk used to feed calves: thermal effects on various mycoplasma.

Discard milk from sick or antibiotic-treated cows is often used as an economical alternative to milk replacer at dairy farms. This practice poses a health risk to calves if the discard milk is from cows with mycoplasma mastitis. Mycoplasma bovis, Mycoplasma californicum, and Mycoplasma canadense are among the agents known to cause contagious mastitis in cattle and occasionally pneumonia, otitis media, or arthritis in calves. This report describes a recent outbreak of calf polyarthritis and respiratory disease on a midwest dairy farm. The farm fed discard mycoplasma mastitic milk to its calves. On-the-farm pasteurization of the discard milk to 65 degrees C for 1 h before feeding prevented additional illness in the calves. Discard milk samples were collected before and after heating and tested for mycoplasma by culture. Only samples collected before pasteurization yielded live cultures. Common mastitic mycoplasma agents were also tested for sensitivity to heat. It was determined that 65 degrees C killed M. bovis and M. californicum after 2 min of exposure, while M. canadense remained viable for up to 10 min. Exposure to 70 degrees C inactivated M. bovis and M. californicum after 1 min, but M. canadense samples were positive for up to 3 min. Thus, M. canadense appears to be more heat resistant than M. bovis and M. californicum. Heat treatment that results in the destruction of M. canadense should be used for the pasteurization of discard mycoplasma mastitic milk.