The National Mastitis Council held its annual conference in January in Tucson, Arizona. A major objective was to examine the 5-point mastitis control plan that has its roots going back at least four decades. The speakers who traced back the origin of the plan noted that it could be judged to have been very successful if you looked at the change in udder health over that time. Bulk tank somatic cell counts (SCC) and other measures of milk quality have shown continual and steady improvement. Some bacteria that were a major cause of infectious mastitis, notably Strep agalactiae, have been virtually eradicated in Canada, the U.S. and European Union. These gains have been accomplished through the hard work of many people but especially by farmers.
Some of our oldest mastitis challenges are still with us though, especially Staph aureus. As farmers were able to gain better control of the contagious causes of mastitis, other bacteria have become more important. Many of those are classified as environmental bacteria — they come from the barn rather than from the infected udder of another cow. One speaker noted that Strep uberus is an environmental bacterium that is being seen more often as mastitis treatment patterns change.
The original 5-point mastitis control program included recommendations on treating clinical cases of mastitis and routine dry treatment of all quarters. These two recommendations came up for discussion since it is now clear that there are a large number of cases of clinical mastitis that will resolve without antibiotic treatment. Even in cases that do benefit from treatment, it is also clear that treating for longer than recommended on the label is not necessarily useful or beneficial enough to be used routinely.
The reconsideration of whether to dry treat every quarter occupied a good part of the conference. The idea sounds good but it is similar to newer recommendations for treating cows with clinical mastitis. How do you decide which cows with clinical mastitis to not treat and how do you decide which cows to not treat with antibiotics at dry off? The answer to the first question has been much discussed before. Culture of clinical cases is the best way. The challenge is how to get the results back quickly enough to make a decision. Research on mild cases has found that delaying treatment for 24 hours does not usually endanger the cow or the quarter. That still may not be long enough to get an answer back in some parts of the country. Newer milk culture technologies intended to be used on dairy farms are being introduced on a regular basis. So far none are perfect but it is better to use one of them than just treat every case.
As a side note, one of the most common complaints that I hear from dairy farmers about paying for milk cultures is that they get angry when they see a report of “No Growth.” I would agree that sounds frustrating but when I look at research on clinical mastitis, I always look for how many ‘no growths’ were seen in the cows enrolled in the research trial. Those ‘no growth’ cows had eliminated the bacteria that caused the mastitis before you took the sample — they didn’t need antibiotics. Because I know that sometimes 30 % to 40 % of research samples are ‘no growth’, I get a little nervous if about the same percentage of dairy farmer samples aren’t ‘no growth’ when farmers take samples. Besides, if you get no growth results, that means not only that those cows didn’t need antibiotic treatment, it means that you can collect a good, uncontaminated milk sample too.
Dr. Robert Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph.