The implementation of control measures for contagious mastitis pathogens has successfully reduced the prevalence of these organisms in U.S. dairy herds. However, the control of environmental pathogens remains a daunting task. Escherichia coli (E. coli) are Gram-negative bacteria, similar in structure to Klebsiella spp. E. coli mastitis is typically associated with a quick onset and often severe clinical signs.
Commonly, these organisms are found in organic matter, including bedding and manure. E. coli are one of the most prevalent bacteria in manure; thus, exposure of the teat end occurs through dirty bedding. Poor udder cleanliness, inadequate stall management, and damaged teat ends are risk factors for E. coli infections in uninfected cows.
E. coliwill infect mammary glands through environmental contact. As with control of all environmental organisms, maintaining a clean and dry environment for bedding cows is of utmost importance. In particular, using inorganic bedding (sand) reduces environmental contamination by these bacteria. However, recycled sand can serve as a source of environmental contamination as organic matter accumulates in the bedding material.
Practices for controlling E. coli include implementing proper milking procedures,maintaining a clean and dry housing environment containing appropriate bedding materials, and vaccinating animals.
At milking time, all quarters should be forestripped to begin the milk let-down process. Using an efficacious and proven pre-milking teat disinfectant following forestripping is particularly important in controlling this mastitis-causing pathogen. The pre-milking teat disinfectant should remain on the teats for 30 seconds and should be removed with either a paper towel or a single-use clean and dry cloth towel. When these guidelines are followed, the time from start of manual stimulation (forestripping or wiping) until unit attachment should be in the range of 60-120 seconds, an appropriate period of time for milk let-down to occur. After the unit is detached, an efficacious and proven post-milking teat disinfectant should be applied, with coverage over at least 2/3 of the teat barrel. In herds with a particular environmental mastitis problem, the use of a barrier teat dip is recommended.
In addition, reducing teat end exposure between milkings, by scraping the back of cow stalls (where the udder rests) and applying fresh bedding frequently, is imperative. Applying bedding conditioners, such as hydrated lime, is an effective method for reducing the bacterial load in the bedding. However, the activity of these products is short lived; thus, frequent application is required. It is recommended that 2 lb per stall be applied, and the product must be applied every other day.
The use of a coliform mastitis vaccine (J5 bacterin) has been shown to reduce the severity of clinical Gram-negative mastitis, which includes mastitis caused by E. coli. It is important to remember, however, that these vaccines do not reduce the incidence of mastitis. Researchers have investigated ideas about vaccination administration schedules and appropriate dosing. A dairy producer should talk with a veterinarian before implementing a vaccination protocol.
New infections can occur at any time during lactation and may also occur during the dry period. However, cows in early lactation are at an increased risk for new infections due to the increased stress and immune suppression associated with the postpartum period. Additionally, cows are at an increased risk for mastitis immediately after drying-off. Following milk cessation, cows do not experience the daily flushing of the gland and are at an increased risk for mastitis in the early dry period. Cows with high milk production are not at greater risk than cows with low milk production.
When E. coli bacteria die, a toxin is released. This toxin is the primary cause of the clinical signs observed in a local mastitis infection. Antibiotics act to kill bacteria; consequently, in the case of these infections, the use of an antibiotic results in the toxin release. Thus, intramammary antibiotic treatment is not a generally recommended practice for local infections. However, in cases in which E. coli infections become systemic, antibiotic treatment and supportive therapy are required. Although there has been discussion in recent years regarding the presence of chronic infections caused by E. coli, it is not yet known how these infections become chronic. Veterinary consultation is recommended prior to the start of any treatment protocol. Due to the nature of these bacteria, emphasis needs to be placed on prevention of these infections, rather than on treatment.
Christina S. Petersson-Wolfe and John Currin, Virginia Tech