Culturing and types of mastitis

by Katie Navarra

Although mastitis results in changes in milk quality, it is not always caused by the same bugs. Mastitis is caused by several pathogen groups gram positive (Streptococcus spp. and Staphylococcus spp), gram negative (E. coli, Klebsiella spp.) and others. Even well-managed herds have some level of mastitis, which decreases milk quality and creates a loss in production and decreases the quality of milk products. Monitoring for and controlling are most important for keeping mastitis cases low, to less than 2% clinical cases on a farm.

“The cost of mastitis ranges depending on the case you can have a mild case that just cost the treatment plus the cost of discarded milk all the way to losing a cow due to mastitis,” said Paula Ospina, a veterinary epidemiologist (DVM, MPH, Ph.D.) and dairy training consultant on milk quality. “A good general figure is $444 per case and this is based on a study that looked at the cost of mastitis in the first 30 days, which is when a lot of mastitis cases happen.”

In support of Cornell University’s PRO-DAIRY program, Ospina provided strategies for culturing for and identifying different types of mastitis. She discussed the differences in mastitis transmission based on mastitis type, and whether it is environmental or contagious.

Contagious mastitis pathogens

Traditionally, contagious mastitis pathogens are transmitted in the parlor because they require milk from one cow to be transferred to another cow, which can happen in milking units. The microorganisms S. agalactiae, S. aureus and mycoplasma are to blame in contagious cases. Attaching units to dry, clean and well stimulated teats and assuring good post-milking teat dip coverage are two practices that can help limit the spread of the infection from one cow to another and lower the number of new cases in a herd. For cows with a contagious form of mastitis, treatment options may be limited, as some pathogens don’t respond to antibiotic treatment (e.g., mycoplasma and S. aureus in older cows) and culling may be the only choice.

“Creating a hospital pen where cows with mastitis are milked separate from other cows will help reduce the spread and is part of good management practices,” Ospina said.

Environmental pathogens

Bedding, feed, dirt, mud and water all allow bacteria to grow. Not all pathogens will cause an infection, but E. coli, which is present in each of these locations, has been linked to causing mastitis. Hygiene is the most effective way to limit a cow’s chances of contracting mastitis from these pathogens. Keeping barns clean is important, as is paying particular attention to cows in the dry period. The last two weeks leading up to calving is when most with coliform and environmental streptococci occur, but typically the clinical signs only show up after calving. Improving hygiene is key at this time. Although the association between pathogen count in bedding and mastitis is still being evaluated, most people agree that clean/well-bedded stalls will help reduce mastitis, according to Ospina.

“There has been evidence of some environmental pathogens behaving more like contagious, where there is a spike of very similar (genotypically) environmental pathogens infecting the entire herd,” she said.

Culturing for diagnosis and treatment

A visual change in milk and/or changes in the udder (swelling, pain, redness) are observable clues that a cow has mastitis. But symptoms are not indicative of the type of pathogen causing mastitis. An aerobic culture combined with biochemical tests is the best way to identify the pathogens. Some labs also use molecular tools to confirm the diagnosis. Treatment is based on the pathogen identified, and using on-label recommendations for treatment is recommended.

“Whatever mastitis tube you use, use it as labeled and for the pathogens on the label. Most treatment tubes treat gram positive organisms,” Ospina said.

There are also cases of subclinical mastitis where no clinical signs are seen that are caused by both environmental or contagious pathogens which result in an increase in somatic cell count (SCC). “Higher SCC in milk translate in less shelf life, less cheese/yogurt produced, and for farms that receive bonuses based on SCC it can mean smaller milk checks. It can have a profound impact on a farm and should not be overlooked,” said Ospina.

Best practices for reducing mastitis

Establishing a good milking procedure is one way of reducing mastitis in a herd. This includes a process that allows the milk harvest technician to attach a well-functioning milking unit to a dry, clean teat.

“There are several permutations on how that happens, mostly depending on parlor size/style, but also on small details like which towels are used and where they are stored, or what kind of machine is used to apply the dip,” she said. “If a milking unit is attached too long without a cow releasing milk, it can damage the teat end that increases the mastitis risk.”

Providing a calm, quiet environment in the milking parlor is as important as the milking procedure, according to Ospina. When cows are scared they release adrenaline, a hormone that blocks oxytocin, a hormone responsible for releasing milk.

“Cows may defecate a lot more when stressed or unsure of their surroundings which will increase the bacterial load in the environment and may increase the risk of mastitis,” she said. “They also may not want to enter the parlor if it’s too loud and this reduces parlor efficiency and stresses employees and can lead to rushing procedures.”

Implementing processes that support an efficient milking routine that helps cows remain relaxed creates a positive environment for staff and animals alike and will help reduce mastitis risk.

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