Staph aureus is a very contagious mastitis-causing microorganism that is easily transmitted from infected quarter to uninfected quarter mainly during milking. It is nearly impossible to cure and hard to keep under control without a veterinarian-approved protocol. You should work with your veterinarian to set up a protocol that will work for your operation. The objective is to break the chain of spreading from cow to cow, such as milkers' hands, cloths for cleaning and drying teats, and milking units. This would include proper milking procedure, well-maintained milking equipment, segregation of clean and infected animals, antibiotic therapy, etc.
Dave Fischer, Extension Dairy Educator, University of Illinois - Illini DairyNET
One of the main routes of transmission of the bacteria Staphylococcus aureus is from cow to cow on the inflation (liner) of the milking machine. Thus, either milk infected cows last, backflush teat cups, or use separate milking units. These are difficult to do. One of the problems is identifying treated cows; culturing more than one sample may be necessary. Many dairies have implemented the practice of having milkers wear latex or plastic gloves that can be disposed of after one milking.
Antibiotic therapy during lactation may appear to "cure" infections if disappearance of clinical signs such as clots, flakes, etc. or evaluation of only one milk culture, especially less than two weeks after treatment, are used as criteria. However, many studies where for example milk was cultured two, three, and four weeks post-treatment suggest that the true rate of cure during lactation is quite low, often reported as bacteriologic cure rates between 6 and 15% of cases. Dry cow therapy has been shown to have cure rates usually reported between 40 and 65% of cases during the dry period. Changes in mammary tissue during the very early dry period make the bacteria more accessible. Research and experience have shown that combining IM penicillin at the last three milkings with intramammary infusion of a beta lactam (penicillin family) dry cow treatment at the last milking when cows are dried off has resulted in further increased cure rates. Other practical research has shown that one and only one tube of dry cow treatment antibiotic per quarter at the time of dryoff is more effective and safer than gradually drying off cows, using multiple tubes per quarter or re-treating at any time later during the dry period. Unfortunately, the only 100% "cure" is culling infected cows, but of course that is an expensive option. After a cow treated with dry cow therapy has calved again, as soon as the milk does not look like colostrum any longer, usually one to two days after calving, its milk should be sampled aseptically for culture. Cows that go through at least one dry-treated dry period and remain culture-positive for Staph aureus are often infected for life in our experience. Infected cows kept in the herd should be milked last or with separate units from cows not known to be infected.
Avoiding transmission from cow to cow on inflations is an extremely important and effective practice to reduce the spread of Staph aureus mastitis.
Dave Wilson, Extension Veterinarian, Utah State University
