In a recent study of large Wisconsin dairy herds, roughly four cows out of every 10 received treatment for mastitis during lactation.

Other studies suggest at least 20 to 25% of cows are culture negative at the time they receive treatment, and some portion of cows get treated for bacteria that doesn’t respond well to antibiotics. Those statistics are scary and difficult to defend to consumers worried about antibiotic use in food animals. “To maintain public trust, veterinarians and dairy farmers must ensure that antibiotics are used responsibly,” says Pam Ruegg, a milk quality and mastitis specialist with the University of Wisconsin.

That means mastitis detection and treatment protocols should be built specifically for each farm with the herd’s veterinarian involved.

Because of the fast pace of milking, parlor workers should not be involved in giving antibiotics. Instead, they should be trained to detect mastitis, collect and properly store quarter milk samples and ensure abnormal milk is discarded.

The herdsperson should then be involved in examining the cow and assigning a severity score. Cows with severe mastitis and symptoms beyond the udder should be treated immediately, Ruegg says. But cows with less severe cases, such as abnormal milk or abnormal milk with an inflamed udder, should not treated until their medical history is reviewed.

Ruegg lists six criteria for antibiotic use:

1. Antibiotic use should involve veterinary guidance. “On most farms, many mastitis treatments involved extralabel use of drugs,” she says. “Extralabel drug usage must be supervised by a local veterinarian that has a proper veterinary-client-patient relationship.”

2. Antibiotics should only be used when there is a reasonable likelihood that a bacterial infection is present. “This criteria cannot be met for most of the 25% to 40% of cases that culture negative,” she says. “Alternative ways to manage these cases should be considered.”

3. Narrow spectrum antibiotics that are less critical for treating human illnesses should be used as a first choice. Narrow spectrum drugs have less potential for resistance and are usually less critical for human health needs.

4. Antibiotics should be used for as short a duration as possible. “There is considerable evidence that extended duration antibiotic therapy increases bacterial cure of invasive species (Staph. aureus and some environmental Streptococcus species). No research has indicated that extended duration therapy improves clinical outcomes of mastitis caused by non-invasive pathogens (coagulase negative Staph. species or most E. coli),” Ruegg says.

5. Characteristics of affected cows should be reviewed before antibiotics are administered. Age, stage of lactation, negative energy balance and a history of previous treatments should all be considered. Cows that have had previous cases caused by Staph. aureus, mycoplasma M. bovis, prototheca or serration, for example, are unlikely to respond to treatment.

“Likewise, it is unusual for antibiotic therapy to be effective for cows that have chronic symptoms of mastitis—three or more cases of clinical mastitis during the current lactation or more than four months of somatic cell counts above 200,000 cells per milliliter,” Ruegg explains.

In these cases, abnormal milk should be discarded until it returns to normal and cows should be watched to detect if the mastitis becomes more severe.

6. Extralabel use should be avoided when an on-label use is a possibility. “Extralabel use should be restricted to justifiable cases, such as cows affected with severe mastitis,” Ruegg says.