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Mastitis: How to Reduce Exposure to Environmental Pathogens

03 June 2014

The term environmental mastitis is used to describe intramammary infections caused by pathogens whose primary reservoir is the environment in which the cow lives.

According to the US National Mastitis Council, these pathogens are routinely found in feces, bedding materials, feed stuffs, dust, soil, and water. This distinguishes them from contagious pathogens (such as Streptococcus agalactiae and Staphylococcus aureus) whose primary reservoir is other infected quarters within the herd, and skin flora opportunists (staphylococcal species other than S. aureus). Of fundamental importance is the fact that environmental pathogens cannot be eliminated from the dairy farm and consequently teat ends are constantly exposed to such pathogens.

Environmental pathogens include two groups of bacteria; the gram-negative bacteria (primarily coliforms), and species of streptococci other than Streptococcus agalactiae. The gram-negative bacteria most frequently encountered are Escherichia, Klebsiella, Enterobacter, Pseudomonas, and Serratia. The most common coliforms isolated from mammary glands are Escherichia coli and K. pneumoniae.

The primary source of E. coli is feces while K. pneumoniae is generally associated with vegetative material such as sawdust. The environmental streptococci are likewise a diverse group with Streptococcus uberis appearing to be most frequently associated with mastitis. Environmental streptococci are found throughout the cows' environment with high concentrations in straw bedding materials.

Environmental mastitis control is complicated by the fact that environmental pathogens are always present in the cows' surroundings. Teats are continuously exposed to environmental pathogens between milkings and throughout the dry period. As a result, methods for controlling contagious pathogens (primarily teat dipping and dry cow therapy) are largely ineffective against environmental pathogens. Post milking teat dipping has little impact on exposure of teats to environmental pathogens and dry cow therapy does not reduce the reservoir of environmental pathogens in the dairy herd.

Herd problems with environmental mastitis differ significantly from problems associated with other types of mastitis. The prevalence of quarters infected with environmental pathogens in a herd at any one point is generally low, seldom exceeding 10 per cent . Coliform infected quarters seldom exceed 2 to 3 per cent .

Prevalence is a function of both the rate of new infections and duration of infections. A major factor in the low prevalence of environmental infections is the short duration of such infections. The majority of environmental streptococcal infections last less than 30 days and the majority of coliform infections last less than 10 days.

Due to the low prevalence of infection, environmental mastitis has minimal effects on bulk tank milk somatic cell count (SCC), which is in contrast with contagious mastitis. The short duration of infection also reduces the reliability of individual cow SCC to detect infected cows, particularly when counts are obtained at monthly intervals.

A comparatively high percentage of environmental infections result in clinical mastitis. Approximately 80-90 per cent of all coliform infections are clinical, with symptoms ranging from mild to peracute mastitis, while about 50 per cent of environmental streptococcal infections result in clinical mastitis.

Control of environmental mastitis is achieved by decreasing the exposure of teat ends to pathogens and/or by increasing the resistance of cows to intramammary infections. The herd environment should be kept clean, dry, and comfortable. Minimize conditions which increase exposure to environmental pathogens such as overcrowding, elevated temperature and humidity in barns, poor ventilation, accumulations of manure, urine and water, poor stall design, access to ponds or muddy lots, and dirty maternity stalls or calving areas.

Teats should be cleaned and dried with individual towels prior to milking. Milking wet udders and teats is likely to increase the incidence of environmental mastitis. Dipping the teats in an effective germicide prior to milking (pre-dipping) reduces the exposure of teats to environmental pathogens during the milking process. Teats that have been pre-dipped must be wiped dry prior to machine attachment to prevent contamination of milk. Milking systems must be maintained regularly.

Malfunctioning equipment can cause liner slips and teat end impacts which increases the likelihood of infection by environmental pathogens. Cows should be fed a well balanced diet. Vitamin E and selenium deficiencies have been associated with both increased susceptibility to environmental mastitis and longer, more severe infections.

Treating clinical cases during lactation is a necessity but of little value in controlling environmental mastitis. Cure rates are generally about 50 per cent for environmental streptococcal infections and 10-20 per cent for coliform infections. All quarters of all cows should be dry treated. Dry cow therapy significantly reduces the rate of new environmental streptococcal infection during the early dry period, but not the week or two before calving. Reinfusion of antibiotics during the latter part of the dry period is not recommended. Dry cow therapy does not control coliform infections.

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