On-farm mastitis cultures reduce drug treatments
Editor’s note: This is the second in a series of articles on mastitis, treatment protocols and new research. You can read the first article, "Mastitis Protocols," from the March 2014 issue under bonus content.
Mike and Sonja Rasmussen have reduced mastitis treatment drug usage by more than half since they started doing on-farm culturing at Hillhaven Farm in Edmore, Mich., nearly 18 months ago.
Now, the Rasmussens only tube cows that harbor Gram-positive mastitis organisms. Cows with Gram-negative bacteria, such as E. coli and Klebsiella, receive supportive care but no tubes.
The approach has not only reduced drug usage; it has also cut the herd’s somatic cell counts (SCC) in half. It has also reduced the potential risk of finding positive drug residues in the animals’ milk and meat.
"Everybody is interested in the bottom line when it comes to milk culturing," Mike says. "It doesn’t take a big investment in equipment and time to get a positive return in potential drug savings."
"Now, we’re only treating the cases we need to," Sonja adds. "And that’s just responsible drug usage."
The Rasmussens milk about 750 cows in central Michigan. Their herd’s bulk tank SCC had been hovering around 200,000 cells/ml on sand bedding.
But four years ago, they switched to deep-bedded, separated manure solids because of the hassles of disposing of sand-laden manure. A year later, their herd’s somatic cell count started creeping up. By April of 2012, the bulk tank SCC ranged from 300,000 to 350,000 cells/ml with an occasional daily count spiking above 400,000 cells/ml.
"We knew we had to do something because those cell counts weren’t acceptable," Mike says. In addition to more attention to delivering drier bedding to freestalls and maternity pen cleanliness, Sonja started culturing clinical mastitis cases.
They had already been doing some individual cow culturing through their co-op, but the turnaround time was too slow. So Sonja invested in a $40 egg incubator and started running samples on-farm.
That approach worked; however, the results weren’t consistent. So the Rasmussens doubled down and invested $350 to $400 in a higher-quality Quincy incubator.
The herd manager samples every clinical mastitis case. Sonja then tries to plate the sample within an hour of sampling on a bi-plate that grows Gram-positive and Gram-negative organisms.
She reads the plate 24 hours later, and if there is a positive identification, reports the results to Mike, who then follows his treatment decision tree. If there is no growth, Sonja incubates for another 24 hours to see if something will grow.
"We will run a few tests per week, with two-thirds being Gram-negative. But about a third are staph species, which Mike usually treats with antibiotics," she says.
The Rasmussens also usually culture the 15 highest SCC cows each month. The herd manager uses a California Mastitis Test on each quarter to determine which is most likely infected. She’ll then pull a sample, which Sonja cultures.
The sampling takes a bit of time, but the bi-plates are just $1.80 each. With this time and effort, the Rasmussens get a monthly snapshot of what’s happening in the herd.
They will also go back in their records to see if these top 15 cows are chronic or new infections and where they are in lactation. That gives them an idea of where to focus management to prevent new cases. "The new infections are usually a staph species, which respond quite well to treatment," Mike adds.
As a whole, the entire mastitis approach—which is a team effort that includes management, milkers and barn crew—is paying off. Their antibiotic drug treatments are down by at least half.
The herd somatic cell count, even after a rough winter, is now down to 148,000 cells/ml with an 80 lb. per cow tank average. The goal this year is to push it below 100,000.
This type of success is possible on other farms as well, says Pat Gorden, director of Food Supply Veterinary Medicine at Iowa State University (ISU). Gorden has also spent seven years as a large herd veterinarian in the southwest before joining ISU. He now heads up mastitis control and treatment efforts for ISU’s 400-cow university dairy herd.
In-house culturing of every clinical case of mastitis has reduced mastitis tube use by 70% to 80%. That’s an astounding feat, but Gorden says the ISU hospital crew was treating many cows for more than 10 days in hopes of getting a cure.
"We started [the] culture-based approach three years ago because our milking crew complained that the intramammary treatments weren’t working," Gorden says. "Once we started culturing, we found that the majority of clinical cases were caused by Klebsiella, and treatment wouldn’t have worked anyway."
Now, all clinical cases are cultured, and antibiotic treatment in the gland is given only if an organism found might be susceptible. Quarters found with no growth or positive to Gram-negative bugs are given supportive care only.
In the university herd, 20% to 40% of samples show no growth, 30% are Gram-negative and the remainder Gram-positive. Only Gram-positive cows are treated.
For cows given antibiotics, there is also an endpoint to treatments—usually four to five days. "We never treat more than five days unless it’s Staph. aureus," he says.
Bacterial cure should occur within five days for most bacteria, although it might take longer for mammary tissue to heal and milk to appear normal.
Gorden admits that one of the biggest and most frustrating problems with sampling is contamination. "Failing to take sterile samples can be humbling for anyone, myself included," he says. "That’s especially true in winters like this past one where we had a lot of teat end issues.
"If you get a lot of contaminated samples with multiple bugs growing on plates, you have to look at your sampling technique," Gorden says.
Plus, you need to have a good-quality control mechanism. Periodically, ask your veterinarian to review your results or have another lab look at dual samples to make sure your on-farm test is getting consistent and accurate results, he suggests.