cows in field

Ask the Vet Column

We are excited to announce that Ask the Vet will become a regular column beginning in this issue of the NODPA News. We welcome Dr. Dayna Locitzer, DVM, and thank her for generously giving her time to answer your questions. Question: My veterinarian wants me to culture my cases of mastitis, what’s the point if we are organic and can’t treat?

My short answer to this is that if you don’t know what is causing your problem, you have no way to prevent it. My long answer is what follows. I just returned from a farm on this rainy December day, and I noted how wet it was outside and because of that, how wet it was inside the barn. When I see that, what immediately comes to mind is that these are prime conditions for mastitis.

The warm, wet conditions of the inside of a barn on a rainy day are the perfect growth media for certain mastitis causing bacteria. These bacteria are categorized as environmental pathogens, and if you know you are dealing with these pathogens you will look at your wet barn with a more critical eye.

But let’s rewind for a second. As organic dairy farmers, you are unable to treat intramammary infections (aka mastitis) with antibiotics and maintain that cow as organic. While this initially might sound like a handicap, it really isn’t because most mastitis causing pathogens are not even treatable with intramammary antibiotics. About 30% of cultures are no-growth; 30% are gram-negative bacteria, which are not susceptible to antibiotics; and 30% are gram-positive, some of which are not susceptible to antibiotics. This culture information is helpful when you are using pathogen based antibiotic therapy, but it is also helpful when trying to troubleshoot mastitis on your farm.

As I stated above, 30% of samples will come back as no-growth. This means the immune system of the cow likely has already waged war against the bacteria and successfully eliminated the invaders. While this result can be frustrating, it also means that your cow’s immune system is robust and doing its job.

Then there are 30% of samples that will be reported as gram-negative, these are typically E.coli and Klebsiella spp. bacteria. These bacteria do not respond to the intramammary antibiotics available to food producing animals and conveniently will often self cure. Both of these bacteria are considered environmental pathogens, but knowing which of these bacteria you have will give you clues as to what area of the farm to target as the cause.

E. coli is your run of the mill bacteria found in manure that can cause mild mastitis all the way to severe toxic coliform mastitis. Environments where manure is not managed well are at risk of causing E.coli mastitis. If you are seeing cultures come back as E.coli, you should consider cleaning bedding areas and alleyways more often, effectively removing debris from udders before machine attachment, and using an appropriate pre-dip. You might also want to consider vaccinating to prevent E.coli mastitis. These vaccines reduce the incidence and severity of disease and have cross protection against other gram negative mastitis causing pathogens, including Klebsiella spp.

If you receive a Klebsiella spp. positive sample, all the above precautions are also effective, but the source of this bacteria often comes from sawdust. In these situations you should evaluate the quality of your sawdust to make sure it is refreshed often and is clean and dry. You should also look into getting kiln-dried sawdust, which poses less risk for Klebsiella overgrowth.

The last 30% will culture as gram-positive. There are many different species of bacteria in this category, but to name a few: Streptococcus uberis, Lactococcus spp, Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Enterococcus spp. and Non-Aureus Staphylococcus spp. To break this category down a little further you have environmental-gram positives and contagious gram-positives. The environmental gram-positives generally include Strep. uberis, Lactococcus spp, Strep. dysgalactiae, and Enterococcus, and to prevent these bugs from causing mastitis the same principles as E.coli prevention apply: making sure bedding areas and alleyways are as clean and dry as possible. In the case of a positive Strep. uberis, straw bedding can often be a culprit, so take extra caution if that is what you use. Unlike the gram-negatives, these gram-positive bacteria typically don’t cause toxic mastitis, but they are also less likely to self cure. In these situations, I would recommend treating with your organic treatment of choice because not addressing it can cause long term high somatic cell count and animal welfare concerns.

As for the gram positive contagious pathogens, including Staph. aureus and Strep. agalactiae, these bugs are host-adapted and thrive in the environment inside the udder. It is very important that you know you are dealing with these bacteria because they spread from one cow to another and cause chronic infections. To prevent cows from contracting these pathogens and from spreading them, strategies related to milking time should be employed. Gloves should be worn; vacuum level should be appropriate; teat ends should be healthy; and a strong post dip should be used. Cows that are known to be positive for these pathogens should be milked last and be considered for culling. If you want to learn more about Staph. aureus, ask me and I can write a whole column on Staph. aureus control!

The last 10% are less common pathogens but are equally important to know about. These include Mycoplasma spp., Prototheca, and Pseudomonas spp. to name a few. Getting a positive of one of these less common pathogens is important because they also have unique implications for your herd health. I would suggest doing a bulk tank culture to see if they are present in your herd.

As you can see, it is important to know what pathogen is causing mastitis in your herd because it helps you target efforts to prevent future infections. It will also help you understand the trends on your farm. Do you constantly have an issue with E. coli? Maybe you should make sure the cows have manure free udders, which means cleaning walkways and beds more often. Maybe your overall cell count has been creeping up. Do you have a contagious pathogen making its way through your herd? Now the question is, what cows should you culture?

I think it is wise to culture all new clinical cases. This means cows that do not have a history of mastitis during this lactation and all of a sudden have a spike in somatic cell count and/or have abnormal milk. I also suggest culturing a cow with chronically high somatic cell count that doesn’t necessarily have abnormal milk. This is a situation where you might find Staph. aureus. Some folks culture all fresh cows as a way to screen cows for Staph. aureus.

I hope this gives you a better understanding of when and why to culture your cows. Take a minute and look around your barn and milking area. Can you take a guess as to what mastitis pathogens might be present in your system? Ask your veterinarian (or me) if you are interested in learning more about this and adding culturing to your mastitis protocols. If you know your enemy, you will be better equipped to fight it.

If you have a question for Dr. Locitzer, please email, call 413-772-0444, or mail to NODPA, 30 Keets Road, Deerfield, MA 01342. PLease include contact information so we can reach you if we need additional information.

Dr. Dayna Locitzer has over 10 years of experience working with pasture-based dairies in the Northeast. Before starting veterinary school, Dr. Locitzer worked for 6 years on organic dairy farms in the Hudson Valley of New York including Hawthorne Valley Farm, Chaseholm Farm, and Churchtown Dairy. It was during that time that she developed a passion for herd health and decided to go to vet school at Cornell University. After graduating, Dr. Locitzer began working at Green Mountain Bovine Clinic in Chesterfield, NH where she treats cows, goats, sheep, alpaca, pigs and horses.