Environmental Streptococcus Mastitis
Dairy Pipeline: August 1997
Extension Dairy Scientist, Milk Quality and Milking Management
Environmental mastitis has become a problem in those well-managed herds who have previously either eliminated contagious mastitis caused by Streptococcus agalactiae or minimized that caused by Staphylococcus aureus. A survey of 67 dairy herds in 14 states by the National Mastitis Council found that mastitis produced by environmental streptococci is as frequent as mastitis caused by Staph. aureus and more frequent than coliform mastitis. These Strep. infections occur mostly during the first two weeks after drying off or last two weeks before calving with a 5.5 fold greater occurrence during the dry period than during lactation, especially during rainy, hot summer and fall months. Approximately one half of the cows who are infected by environmental Strep. bacteria will have clinical mastitis (abnormal milk, swollen mammary gland, fever, anorexia) during the next lactation with much of it found in the first week after calving. Cows, more so than heifers, can be exposed to environmental streptococci (82% are Streptococcus uberis) through bedding materials (heavily soiled straw and sawdust packs especially in maternity stalls), manure, soil, lips and tonsils, nostrils, genital tract, and teats. Exposure to environmental streptococci can be minimized by controlling flies and other insects; providing clean, dry, comfortable housing (especially calving); and using proper milking time hygiene including predipping (teat spraying has been shown to increase infections). Most infections which develop in the early dry period can be prevented by dry cow antibiotic therapy to all quarters. Diet can influence the resistance of cows to mastitis infections. Diets deficit in vitamin E and selenium increase risk of environmental streptococcus mastitis due to reduced phagocyctic cell function which is the body's defensive ability to kill off infection. Blood and tissue concentrations of vitamin E and selenium appear to be lowest around calving. In addition, many dairy cows have low blood calcium at parturition which can impair smooth muscle contraction that is vital to closure of the teat sphincter after milking. From 10-50% of Holstein cows remained subclinically hypocalcemic for as many as 10 days after calving. Other dietary deficiencies (zinc, copper, beta-carotene, and vitamin A) have been suggested to have an influence on resistance to infection. A negative energy or protein balance impairs immune function. An accumulation of ketoacids in blood further impairs lymphocyte function. According to Drs. Larry Smith and Joe Hogan, Ohio State University, effective control of environmental streptococcal mastitis in the short term is most likely to be achieved by reducing teat end exposure.