Historically, a veterinarian was typically called to a dairy farm to treat individual cows with mastitis. In modern dairy farming, most individual cases are taken care of by farmers directly, based on treatment protocols that were designed with the help of a veterinarian. The veterinarian is still involved, but more on a herd-level basis instead of seeing individual animals. This trend is encompassing many vets in the dairy industry. It has already happened in the poultry and pork industries, so many of us feel that the wave will hit the dairy industry in our lifetimes. Our focus has shifted to treating the herd and preventive medicine.
No effective antimicrobials are labeled for systemic treatment of mastitis in the United States. Those that are approved for other conditions do not reach sufficient levels in the mammary gland. Other countries do have effective labeled antimicrobials for systemic treatment of mastitis, however. Antibiotic selection is important when treating mastitis for multiple reasons, but the most important is that each antibiotic has a different milk withdrawal and not every antibiotic will be effective against the organism infecting the udder. Each farm has its own collection of mastitis organisms due to the variability of farm environmental conditions. Some farms have contagious mastitis organisms that can spread cow-to-cow, while some have environmental mastitis organisms that infect cows from the environment.
Clinical mastitis can be easily seen via swollen, hot, or discolored udders as well as abnormal milk. Some cows may even be systemically ill if particularly virulent bacteria are present. Subclinical cases are harder to detect; these cows have an infection, but it is not visibly apparent. We can detect these infections with simple tests like a California Mastitis Test. We do this test on most cows that come to the large animal hospital at Cornell. It is a fast, cheap test that gives one few reasons to justify not doing it. It can show us whether or not the cow has an increased somatic cell count (SCC) in an udder. This generally represents white blood cells, which will be in the udder in high numbers if the infection is present. When an animal comes to the hospital, it is treated as an individual much more than when it is on the farm. As vets, we must be able to focus on both the herd health and the individual health of the animals.