If a dairy farmer’s milk looks odd, it’s time to check for mastitis.
Mammary infections don’t always result in what is called “clinical” mastitis, where the milk is visibly affected. It can have coagulations or flakes, or can appear watery.
“We really need to be sure that we know what organism we’re working with, because there are different antibiotics on the market that are targeting different organisms,” Reagan Bluel, University of Missouri Extension dairy specialist in Barry County said. “What you’re up against is going to dictate which antibiotic is appropriate, or even ‘if’ an antibiotic is appropriate.” Bluel added that some cooperatives will analyze samples for farmers.
Clinical mastitis is distinguished from subclinical mastitis, where the infection still produces an inflammatory response but is not apparent from the appearance of the milk. Dr. Sarah Place, assistant professor of sustainable beef cattle systems at Oklahoma State University, said if an animal diagnosed with clinical mastitis has to be treated with antibiotics, the milk is not fit for human consumption and cannot enter the food supply.
“There are different types of antibiotics out there that are more effective on gram-positive versus gram-negative type bacteria, so by doing a culture we can determine which type of antibiotic would be the most useful at that time,” Place told OFN.
There are two major classifications of the types of pathogens that will cause mastitis. The first is contagious pathogens like Streptococcus agalactiae, Staphylococcus aureus and mycoplasma species such as M. bovis. Place said these pathogens are called contagious because they can live in the milk, so they can be spread from animal to animal by a milking machine or by the milker’s hands.
“If you milk an animal with one of those mastitis pathogens living within the udder and then milk another cow that’s not infected afterwards without changing gloves, or if you’re not using gloves during milking, you can spread that pathogen to the next animal,” she said. “That’s why it’s important to isolate those animals, and understand what type of pathogen they have.”
The other broad classification of mastitis pathogens is environmental species, many of which fall within this category. It’s all the pathogens that are in the environment and ubiquitous like E. coli, which can come from the gastrointestinal track of the animal and can be in manure. There are also other Streptococcus and Staphylococcus species that are classified as environmental, but they don’t live in milk and so aren’t thought of as spreading from animal to animal. However, they can still cause mastitis and an alteration of the milk, along with systemic illness in cows.
There is no known treatment for some other mastitis pathogens, including M. bovis, which is very contagious and will spread within the herd, so typically animals diagnosed with that pathogen are isolated from the herd and have to be culled.
Place said while other environmental species can be treated effectively, but there are exceptions.
“E. coli is one of those pathogens for which you don’t want to treat the animal with intermammary infusion of antibiotics, because that actually can cause the animal to become more ill,” she said. “Usually with an E. Coli infection, that animal gets visibly ill; they go off feed and may have a fever. You usually give the animal supportive therapy, meaning painkillers and fluids to keep them hydrated, and hopefully they’ll fight off the infection themselves.”
