The treatment of clinical mastitis has dramatically changed in the approximately 50 years of my veterinary career. The major focus has been on the proper and judicious use of antibiotics in dairy cattle and assuring the public there are no antibiotic residues in the milk supply.
The wild west
For the first half of my career, clinical mastitis was aggressively treated with intravascular antibiotics as well as intramammary therapy. It was thought the harder the mastitis pathogen was treated, the better the cure rates would be. It was a “wild west” approach that most of us followed.
It was common practice to use commercial treatments as well as extra-label treatments to reach a wider spectrum of antibiotics and kill resistant bacteria. When a cow had a clinical case of mastitis, the dairy farmer was instructed to strip the quarter out completely and then treat with the appropriate intravenous or intramuscular antibiotic, along with a corresponding intramammary treatment. We also instructed dairies in severe cases to strip the bad quarter out every one to two hours during the day to remove any existing pathogens and reduce the swelling in the quarter. The biggest concern with these types of treatments was withhold times for milk and meat to eliminate any treatment residue.
There were many methods on how to select the proper therapy. This was based on clinical signs or performing a milk culture to identify the pathogen and then a bacteria susceptibility to select the best antibiotic option. The latter was a widely used method by most veterinarians and tended to yield the best results.
Reining it in
About 20 years ago, there was an international push to be more selective on which animals get antibiotic treatments. The press was talking about the worry of worldwide antibiotic resistance from improper use of antibiotics in animals, sparking a huge debate. At this time, there was also a push from the Food and Drug Administration to enforce stronger policies against extra-label treatments of animals. This forced producers to use approved commercial treatments that had known milk and meat withholds. This dramatically limited the number of antibiotics which could be used, and people were convinced this would lead to poor cure rates. However, time showed that the cure rates were no different than when a wide variety of non-approved antibiotics were used.
This new approach to clinical mastitis led to better milk quality management. This delayed antibiotic treatments by 24 hours as producers waited for culture results and then selected the appropriate antibiotic for the pathogen causing the mastitis. There was a fair amount of resistance to this method because farmers were concerned that the 24-hour delay would cause more severe cases of mastitis.
When I was president of the National Mastitis Council in 2003, I held an international clinical mastitis treatment symposium at our annual meeting to discuss proper treatment of clinical mastitis from different viewpoints around the world. The research clearly showed that a 24-hour delay in treatment did not have any negative impact on cure rates and allowed a better cure rate because of the more proper treatment choices. This became the standard treatment of the dairy industry for many years.
A cautious approach
Around 10 years ago, as more cases were being treated based on culture results, new findings were discovered by both dairy farmers and veterinarians. The most impactful observation we noticed was that certain bacteria had high cure rates while other bacteria did not. The research being done around the country was also finding similar things, and it was determined that many bacteria have a self-cure, finding the cure rate as high or higher than using antibiotics.
This created a new approach to treatment for clinical mastitis. We learned that determining whether the pathogen causing clinical mastitis was gram-positive or gram-negative was key to identifying the correct treatment. The new protocol was to limit antibiotic use to gram-positive bacteria and use no antibiotic treatment of gram-negative. The key was to keep gram-negative and gram-positive clinical cases out of the bulk tank when the milk was abnormal and to only use antibiotics when necessary.
For the gram-positive bacteria, the appropriate antibiotic intramammary therapy was selected and the infected quarter treated for the required amount of time. In most cases, only intramammary treatments were used and rarely were intravenous or intramuscular supportive therapy used. Results were very positive when this method was followed. In cases of gram-negative bacteria, only supportive therapies were used with no antibiotics. The results were equally as good as when antibiotics were used. In severe cases of gram-negative bacteria cases, supportive treatments such as intravenous fluids, oxytocin and occasionally anti-inflammatory products were used.
In the past five years, the shift has even been bigger toward no antibiotic treatments being used at all. Recent research is now showing the self-cure rate on most cases of clinical mastitis is about the same as when treated with antibiotic therapy. Now there are a great number of dairies that do not treat any clinical case of mastitis with any antibiotics. They instead monitor each cow by pulling her from the milking string and putting her into the hospital. Swollen quarters sometimes receive liniment-type products on the exterior surface of the infected quarter, use oxytocin at milking in the hospital parlor and some anti-inflammatory products. This approach is working well if properly managed by each dairy.
One of the drawbacks of no antibiotic therapy is the potential of chronic cases of mastitis developing, especially with some of the gram-positive bacteria. It’s important that each dairy keeps good treatment records and looks at the outcome of each case of clinical mastitis. If there seems to be a trend toward more chronic cases of gram-positive bacteria, I would suggest implementing a properly designed treatment protocol for this type of mastitis. As I said earlier in this article, all abnormal milk must be kept out of the bulk tank and not offered for sale.
The key to any successful therapy program is a good partnership between dairy farmers and their veterinarians. Together, a proper and well-designed therapy program can be designed for your farm. Remember, not all farms are the same, and that is why each farm needs to develop their own treatment protocol that fits their specific needs.
