Skip navigation links

Sept. 20, 2023

MSU research: saving money, milk and improving human health

Pamela Ruegg with researchers in Brazil
Pamela Ruegg is the David J. Ellis Professor of Antimicrobial Resistance and Large Animal Clinical Sciences in Michigan State University’s College of Veterinary Medicine. Ruegg is pictured with Jose Pantoja, a professor at a veterinary school in Brazil, and Lara Juliana Bastos, who is a current doctoral student of Ruegg’s and completed her master’s degree with Pantoja. They are on a farm in Brazil. Courtesy of Ruegg.

New research from the College of Veterinary Medicine at Michigan State University finds that dairy producers overtreat cows diagnosed with non-severe cases of clinical mastitis, which increases farm costs and loss of milk.


Pamela Ruegg, the David J. Ellis Chair in Antimicrobial Resistance and professor in the Department of Large Animal Clinical Sciences, estimates the direct costs of treatment could be reduced by $65.20 per case if the minimum labeled durations are used, which she said provides the same health outcomes as current practices. The cost of mastitis to the U.S. dairy industry is approximately $110 per cow per year — and that dollar amount increases annually.

In dairy cows, mastitis is the inflammation of mammary glands in the udder, usually caused by a bacterial infection that leads to decreased quantity and quality of milk. Milk produced by cows while they’re being treated with antibiotics must be discarded, as well as the milk produced after treatment during the withholding period — usually three to four days after the last treatment has been given.

Pamela Ruegg with students collecting samples at MSU Dairy.
Ruegg with Cara Robison, a technician, and two now graduated doctorate students, Quinn Kolar and Juliana Leite de Campos, collecting samples at the MSU Dairy. Courtesy of Ruegg.

Published in the Journal of Dairy Science, Ruegg analyzed non-severe cases of clinical mastitis for approximately 50,000 cows on 37 commercial dairy farms in Wisconsin. She found that milk discarded due to antibiotic treatment represents at least 53% and up to 80% of total direct costs for each day of treatment.

The bottom line: Ruegg found that for routine treatments, following the minimum labelled duration for mastitis treatment drugs is critical to farm cost savings and productivity, as well as maintaining animal and human health.  

“Our work indicates that we need to take a hard look at duration of treatment, and unless you can justify improved clinical outcomes, we should treat using the minimum duration listed on product labels, and for shorter durations,” Ruegg said.

“With that, there’s both a financial savings for the producer, and there’s a human health benefit because we’re putting less antimicrobials into our ecosystems. There are benefits for society, and guess what? You’ll have the same outcomes.”

The opportunity to save on the costs of treatment and regain revenue from less discarded milk is hard to ignore for producers who are already facing steep fiscal challenges. Dairy producers in the U.S. are battling against federal milk pricing regulations and pandemic aftermath, losing on average more than $6 per hundredweight (milk sales unit) on farms of more than 50 cows.

Pamela Ruegg at a Michigan dairy farm with students.
Ruegg at a dairy farm in Michigan with Leticia de Souza Ferreira, who will complete her master’s degree in November, and Juliana Leite de Campos, who completed her doctorate degree last year. Courtesy of Ruegg.

And mastitis isn’t going anywhere, Ruegg said.

“The proportion of cows with clinical mastitis isn’t going down. At best, it’s stable, and at worst, it’s increasing, probably because of environmental pathogens that tend to cause larger inflammatory responses.”

Mastitis is an expensive disease. Ruegg said because cows now produce almost twice as much milk since she started practicing in 1984, the same treatment protocol today costs approximately 40% more.

“We have five products labeled to treat clinical mastitis in the U.S. The FDA-approved labeled duration of treatment with those drugs ranges from one day to up to eight days. People generally treat for five days because the milk remains visually abnormal on average for five days. Dairy farmers feel like they should treat until it looks like it’s cured. But a lot of our previous work has shown that the abnormal milk appearance is from inflammation, and it’s not predictive of any outcomes like the presence of bacteria or infection recurrence. Again, there’s no benefit.

By: Emily Lenhard and Kim Ward

Media Contacts