As dairy farmers, we need to learn to manage mastitis using a whole arsenal of information rather than routinely treating all our mastitis cases with antibiotics. One step in intelligently managing mastitis, according to Dr. Ernest Hovingh of Penn State, is to learn to culture the organisms causing mastitis on your farm. Which organisms are causing mastitis is one important piece of information you’ll need to figure out the best way to manage your mastitis cases.
“Often what I find when I go to dairy farms and talk to dairy farmers,” commented Dr. Hovingh at the Penn State Mastitis and Milk Quality Conference, “is that the farmers aren’t really convinced they have a good mastitis plan. Although some have a pretty good handle on mastitis management, some have stopped treating their mastitis cases altogether, thinking it does no good. Others treat every single cow that has flakes and clots in its milk,” which is not very cost-effective, and can lead to the loss of milk or to residue problems.
“We need a logical way to work through the process of deciding whether or not to treat a given cow,” he continued.
Staphylococcus aureus lives almost exclusively in the udder, and it’s transmitted from cow to cow, mainly at milking time. It is well adapted to its “job” of causing contagious mastitis, and it has a lot of tricks up its sleeve that help it avoid the surveillance of the cow’s immune system. Because of these evasive strategies, you can think a cow is cured when the S. aureus has merely gone into hiding.
S. aureus can produce toxins that can cause a lot of damage in the udder tissue. It can revert to what’s called the “L form,” which has no cell wall. Penicillin, usually effective against this pathogen, won’t work against this particular form. The pathogen can form slime capsules, which keep the bacteria from being devoured by the cow’s immune cells. The S. aureus bacteria can form an abscess deep inside the udder, where they are walled off from the immune system, and the bacteria can hide away. “You can think for a while that you’ve cured the cow,” Hovingh continued, but the abscess can rupture, and the bacteria, which never really left, can start colonizing the udder again.
S. aureus also colonizes and grows well on damaged teat skin. It can be killed by antibiotics at the right stages in its growth and development. However, Dr. Hovingh emphasized, if a cow is severely sick, she should be treated, first with fluids, and then with anti-inflammatories and antibiotics, in case the mastitis is caused by a bacteria that has spread through its body.
S. agalactiae is an obligate udder pathogen. It is only found in the udder and primarily affects the ductwork, rather than the alveoli. Untreated, it causes a lot of swelling in the area. The milk is then prevented from draining through the ducts. The cow can end up with fibrosis and scarring, or even the death of tissue in that area. Although it’s not common, you should know what S. agalactiae looks like, so if you’re culturing samples from your herd, you can deal with it quickly.
These pathogens are fairly common. In the cow world, most are found on the teat and udder skin. Although there are a lot of types of Coagulase-negative Staphs, they’re typically lumped together and treated in much the same way. Coagulase-negative Staphs rarely cause clinical mastitis, and interestingly enough, according to Dr. Hovingh, these pathogens may actually protect a cow against infection from major pathogens! This is because their presence keeps the immune system “revved up”, with the white cell count elevated a little in the udder. These extra white blood cells have a protective effect so the cow is less likely to come down with severe coliform or yeast infection. However, he also said this is not a good enough reason to allow CNS infections to persist in your cows!
There are a number of different pathogens in this group, which are common in the environment and in manure, but the most common are E. coli and Klebsiella. Although Klebsiella has usually been considered an environmental pathogen associated with soil and tree by-products, studies at Cornell have shown that this “critter” can become resident in a cow’s gut. Even with a change in bedding, the cow can still be shedding Klebsiella in its manure, which makes it more difficult to deal with than if it was exclusively environmental.
A characteristic of all coliforms, “what they do really well,” as Dr. Hovingh put it, “is double their numbers every 20 minutes or so. At body temperatures, numbers can really explode between milkings.”
But treatment with antibiotics is not necessarily the best choice for these pathogens. “If you put some coliform bacteria into a gland,” explained Hovingh, “and take samples every half-hour to hour, you will see that it will grow explosively for a while, and then the numbers can drop off, even without any treatment. However, the symptoms of coliform infections usually occur as the numbers are already dropping off. The bacteria release toxins when they die, and these toxins produce the clinical signs of mastitis. “So by the time we can see that the cow has mastitis, if it’s caused by coliforms, there may be no living bacteria there anymore. They may be dead and gone.”
Environmental strep, such as S. uberis and S. dysgalactiae, live in the bedding and also on the cows’ hair, lips and flanks. They can colonize damaged teat skin. “There are so many of them out there, we can’t get rid of all of them, and unfortunately, they can be difficult to cure. If you’re seeing, say, S. uberis out there more frequently in your cultures,” Hovingh advised, “you may need to try a different treatment approach so the cows don’t relapse.”
More information on more bovine afflictions and advice on how to prevent them will appear in the next week issue of Country Folks.