It is important to understand the complexity of environmental mastitis before addressing the question of control. The environmental mastitis pathogens are the coliforms, streptococci other than S. agalactiae and the enterococci. The common coliforms associated with mastitis are Escherichia coli, Klebsiella spp. And Enterobacter aerogenes. The environmental streptococci include Streptococcus uberis, Streptococcus dysgalactie and Streptococcus bovis. Enterococcus faecium and Enterococcus faecalis are the common enterococci. One difference between contagious and environmental pathogens is that the primary reservoir for contagious pathogens is the infected udder and exposure is during milking. In contrast, the environmental pathogens survive and multiply readily in extra-mammary sites, especially bedding, and the exposure to these organisms usually occurs between milkings (Hogan and Smith, 1987).

MASTITIS DUE TO ENVIRONMENTAL STREPTOCOCCI

The rate of new intramammary infection (IMI) is higher in the dry period than during the lactation. New infection rate is highest during the first two weeks of the dry period and again during the two weeks before parturition. Rate of new IMI is also greater in early lactation than during the remainder of lactation. Approximately 60% of infections by environmental streptococci last less than 30 days and about 18% last more than 100 days. Approximately 50% of infections by environmental streptococci cause clinical mastitis. The percentage of mammary quarters in a dairy herd infected with these environmental organisms at any particular time (i.e. prevalence) tends to be low and is generally less than 10% for the total of all environmental organisms (Smith et al., 1985a; Hogan and Smith, 1987).

COLIFORM MASTITIS

Rate of new IMI is about four times higher in the dry period than during lactation, and the rate is greatest during the first two weeks of the dry period and the two weeks before parturition. During lactation the rate of IMI is highest in early lactation
and decreases as lactation progresses. Duration of coliform infections tends to be short; 57% of infections last less than 10 days and 69% are less than 30 days in length. In about 13% of cases the duration is greater than 100 days. A high percentage of coliform infections during lactation result in clinical mastitis (80 to 90%).However, only 8 to 10% result in peracute or ‘toxic’ cases. It is not unusual for E. coli to be eliminated from the udder by phagocytic cells by the time clinical signs are apparent. Thus, the bacteriological culture of clinical milk samples may naturally result in some proportion that are negative (no growth).