Proactively monitoring your animals for Staphyloccoccusaureus is the best plan of action for controlling this mastitis pathogen because it can silently affect cows and infect others for years before clinical signs appear. Still, this can be a tricky pathogen to test for, so farmers and veterinarians must know how to get the most accurate results.
Justine Britten leads Udder Health Systems, a milk quality diagnostics lab with locations in Washington, Idaho, and Utah. On an episode of the American Association of Bovine Practitioners podcast, “Have You Herd?”, she discussed some of the most effective ways to identify Staph. aureus cows and the importance of handling them appropriately. The approach varies by animal age.
Even if there is no Staph. aureus in a herd, heifers can calve in with it at any time, Britten said. That’s why she advocates for culturing milk from all fresh animals. “Regular culturing and screening is the most proactive approach that the dairies can take,” said the milk quality specialist. Research cites that anywhere from 2% to 15% of animals freshen with Staph. aureus.
However, she noted that Staph. aureus sheds intermittently, creating a challenge for accurate testing. Britten also explained that not all Staph. aureus strains are beta hemolytic, so an additional coagulase test in the lab is a good idea to help catch all positive animals.
In addition to culturing, matrix-assisted laser desorption ionization (MALDI) and polymerase chain reaction (PCR) tests can also be helpful in identifying Staph. aureus in certain scenarios, she said. PCR tests should be used with caution because they do not differentiate between live and dead DNA, and Staph. aureus is often present on our skin or cow’s skin, Britten continued.
The lowest barrier to entry for finding Staph. aureus is monthly bulk tank culturing. This provides you with a high-level overview of the pathogens present in your herd and can alert you when there may be a problem. Said Britten, “We monitor so many other things on a dairy, why wouldn’t we monitor mastitis?”
What can I do?
If a first-lactation animal tests positive for Staph. aureus, Britten said it may be worth treating with antibiotics and retesting. However, she noted that even the best farms she works with only see a cure percentage rate in the 60s.
Retesting any animals can become a rabbit hole, she said. The complexities of the pathogen mean a cow may test positive and then, later, be negative with no actual change in status. The longer Staph. aureus is in the udder, the worse the infection becomes, making it crucial to identify positive animals as early as possible and form a plan of action.
Britten advised against attempting to treat any animals that are past their first lactation. These animals should either be culled or, occasionally, may be segregated into a pen with other positive cows to be cared for and milked separately. To make the segregation approach work, though, she emphasized that the farm team must be committed to keeping all positive cows in the designated pens for the rest of their productive lives.
The goal to control Staph. aureus is to create a safe, pathogen-free area for negative animals to rest and live, Britten explained. A Staph. cow is always a Staph. cow, and contamination in the parlor is the number one way of spreading that infection to other herdmates. Identifying those infected animals makes it possible to stop the spread before it happens.
