From the NMC Newsletter "Udder Topics", April, 1999

Arcanobacterium pyogenes (formerly Actinomyces pyogenes) often cause severe clinical mastitis characterized by thick, purulent secretion. The foul odor sometimes associated with this condition is probably caused by anaerobic bacteria that are also present but not detected by routine cultural methods. The disease is most frequent in dry cows or heifers before or at the time of calving, and occasionally occurs in lactating animals as a sequel to teat or udder injury.

Prognosis is poor once an infection is established. Antibiotic therapy of A. pyogenes infections is usually ineffective, and cows often lose the function of the affected quarter. Sources include wound infections, teat injuries, udder infections, abscesses, and genital tracts. Spread appears due to contact of teats with a contaminated environment, such as calving areas and dry cow housing. Arcanobacterium pyogenes may also be transmitted by flies. Mastitis caused by A. pyogenes is more common in humid weather. In Great Britain and northern Europe, the disease is common in dry cows and heifers maintained on pasture and is known as "summer mastitis."

Control measures include fly control programs, maintaining cows in clean and dry calving areas, drying up affected quarters to reduce the risk of spreading the infection to other cows, and removing affected cows from the herd.

Sources: NMC publications "Current Concepts of Bovine Mastitis" (1996) and "Laboratory Handbook on Bovine Mastitis" (in press)