If you look hard enough, you can find Staphylococcus aureus (Staph aureus) in at least one cow on every dairy, according to Dr. Justine Britten a PhD animal scientist working at Udder Health Systems Inc.
Despite that bold statement, Britten is not implying every dairy has a mastitis problem or is gearing up for an outbreak. Rather, she is pointing out how common the pathogen is on the farm and that it often flies under the radar, contributing most frequently to subclinical disease.
“One thing I’m still surprised about, is I think that most producers, veterinarians, and consultants know that, and they don’t necessarily,” she tells Dr. Fred Gingrich, Executive Director for the American Association of Bovine Practitioners, during a recent “Have You Herd” podcast: Managing Staph aureus Mastitis in Dairy Cows
Britten says that the prevalence of Staph aureus is increasing, based on the 7,800 bulk milk samples her company tests, on average, each year. From 2017 to 2021, the prevalence stayed relatively flat at about 20%. Today, the prevalence is more than double that.
“We’re seeing it now at around 44% to 45% of all bulk tank samples we do are positive for Staph aureus,” she says.
Consider The Heifer Population
Something Britten says has surprised her is that heifers may calve into a subclinical infection, resulting from Staph aureus, even in a closed herd.
“Being a closed herd will help reduce the chances that’s going to happen, but it’s still possible,” she says.
In evaluating literature, Britten says between 2% and 15% of heifers are going to calve in with it, and they may have a clinical episode. However, cell counts in the infected heifers tend to be low which lessens detection.
“That’s one of the most frustrating things, is that positive heifers may stay around 100,000 or less with their cell count for quite a while before it begins to climb, and that makes it really difficult for producers to get their minds around the fact that this animal is permanently infected with a contagious pathogen. It also makes the disease that much more difficult to manage,” she says.
If the dairy is not proactively screening, heifers typically recover from an episode and look fine. At that point, they are usually returned to the herd where they may infect other heifers and cows.
“My takeaway is if Staph aureus was easier to see, more like a mycoplasma, I suspect producers would be a lot less tolerant of it than they currently are,” she says.
Screen All Cows And Heifers
Britten considers a monthly bulk tank culture as the bare minimum that a dairy can do towards monitoring pathogens in the bulk tank, and she calls it an incredibly helpful tool.
“You’re really operating in a vacuum otherwise,” she says. “Even by monitoring at the bulk tank level, we’re monitoring at the 10,000-foot view. But if [the dairy] is not doing any other culturing, it’s still better than nothing.”
Britten says she is a strong advocate for screening all cows and heifers as that’s the most proactive approach to prevention.
“It works, I know that it works, but it is very important to have some kind of audit system in place, so that you get them all, not 50% of them, not 70% of them, all of them, and that you have a management plan in place for what to do with them,” she says.
On the dairies she works with that have a very low staff positivity rate, they often sell the cows.
“They’re not going to tolerate them, while for others it’s too expensive to do that,” she says. “They’re going to go into a staff pen, or with the heifers, they try and treat them and see if we can get them cleared up. But yeah, screening, culturing of all fresh cows and heifers is the best way to find those animals early and to manage them.”
Take-Home Messages
In the podcast, Gingrich and Britten discuss that in outbreak situations it is important to evaluate why cows are getting infected and remember that cows typically get infected in the parlor and focus efforts there. This includes evaluating teat condition, parlor procedures and equipment function.
Aggressive culturing programs, segregation and culling are important to minimize risk.
Britten provides these three additional take-home points, per the AABP discussion:
Take-home point #1 – Not all Staph aureus colonies exhibit beta-hemolysis, therefore, it is important that all Staph colonies undergo coagulase testing to identify Staph aureus.
Take-home point #2 – Monthly bulk tank cultures are a bare minimum monitoring program for dairy farms.
Take-home point #3 – Somatic cell count is a lagging indicator and cultures will detect infections earlier. Britten emphasized that the difference lies in management practices. Proactive monitoring, culturing, and implementing strict control measures can prevent Staph aureus from becoming a major issue, even though the pathogen is present.
For more information and recommendations, be sure to check out the podcast: Managing Staph aureus Mastitis in Dairy Cows
