“When we culture mastitis, cases come in three flavors, so to speak: Gram-positive, Gram-negative and no-growth,” stated Stephen Foulke, DVM, DABVP, Boehringer Ingelheim. He says to focus on the first flavor.
“We now know that Gram-negative and no-growth mastitis typically does not require treatment,”1,2 he added. “We could potentially cut up to 60 percent of treatment costs by only focusing on Gram-positive pathogens.”3
A targeted approach
“Targeting and treating Gram-positive mastitis cases can save money on antibiotics and discarded milk as well as reduce hospital-pen density,” said Daryl Nydam, DVM, PhD, professor at Cornell University College of Veterinary Medicine and faculty director at Cornell Atkinson Center for Sustainability. “It also demonstrates the dairy industry’s commitment to thoughtful antibiotic use.”
Targeted mastitis therapy is a two-step approach: First, it’s identifying the mastitis-causing pathogen through culturing; then, it’s making a thoughtful treatment decision based on the results.
Step One: Identify the pathogen
For mild to moderate mastitis, culturing helps identify the right animals to treat. “In broad brush strokes, when you culture, the results are generally equally distributed as one-third no-growth, one-third Gram-negative and one-third Gram-positive,” Nydam explained.
• No-growth: A no-growth case means that the cow has cleared the infection on her own, and does not need antibiotic treatment.2 “Occasionally, it might be due to a different pathogen like Mycoplasma that doesn’t grow under standard conditions, or an intermittently shed bacteria like Staphylococcus aureus,” said Nydam.
• Gram-negative: “A Gram-negative infection stimulates an acute immune response that can cause inflammation and more systemic signs,” he continued. However, most Gram-negative mastitis cases, including those caused by Escherichia coli, will self-cure, and antibiotic treatment will not alter the outcome.1 Not only that, but most antibiotics have limited efficacy against this pathogen.
• Gram-positive: Gram-positive mastitis cases do require antibiotic treatment and can become chronic if left untreated. Often, Gram-positive infections stimulate a less-acute immune response that results in prolonged inflammation and localized signs.
Step Two: Make a thoughtful treatment decision
“When looking for an antibiotic, find a product that is effective against Gram-positive bacteria, such as staphylococci and streptococci,” advised Foulke. “Ideally, the tube has a tip that allows for partial insertion, since long tips can actually drag bacteria up into the teat. Before using any kind of treatment, try to be diligent about properly disinfecting the teat ends with an alcohol pad. We also want a short-duration treatment (1 to 3 days) to get cows back in the tank as soon as possible.”
1 Fuenzalida MJ, Ruegg PL. Negatively controlled, randomized clinical trial to evaluate intramammary treatment of nonsevere, gram-negative clinical mastitis. J Dairy Sci. 2019;102(6):5438-5457.
2 Fuenzalida MJ, Ruegg PL. Negatively controlled, randomized clinical trial to evaluate use of intramammary ceftiofur for treatment of nonsevere culture-negative clinical mastitis.
J Dairy Sci. 2019;102(4):3321-3338.
3 Vasquez AK, Nydam DV, Capel MB, Eicker S, Virkler PD. Clinical outcome comparison of immediate blanket treatment versus a delayed pathogen-based treatment protocol for clinical mastitis in a New York dairy herd. J Dairy Sci. 2017;100(4):2992-3003.