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Ruegg: Mastitis bacteria changing? Yes. Increasing resistance? Not so much – 7 minute audio

[audio:|titles=Pam Ruegg on new mastitis discoveries]

Pamela Ruegg, Professor, Extension Milk Quality Specialist
Department of Dairy Science
UW-Madison College of Agricultural and Life Sciences
(608) 263-3495

Evolution of costly dairy cow disease

6:44 – Total Time

0:17 – What mastitis is
0:35 – Bacteria involved
0:52 – New discoveries
1:07 – A look at modern dairies
1:35 – Surprises in the research
2:43 – The new bacteria
3:12 – Implications
3:39 – Reasons for the change
4:18 – Antibiotic resistance not increasing
5:08 – Advice for dairy producers
5:39 – Future of mastitis management
6:08 – Consumer assurance
6:35 – Lead out



On the trail of a costly dairy cattle disease. We’re visiting today with Pamela Ruegg, Department of Dairy Science, University of Wisconsin Extension in the College of Agricultural and Life Sciences, Madison, WI and I’m Sevie Kenyon.

Sevie Kenyon: Pam, tell us what this disease is?

Pam Ruegg: Mastitis is the most costly disease of diary cattle. I think when we’ve gone out and talked to diary farmers and collected information on it, the interesting thing about this disease is virtually every farm experiences it. They experience it typically in a fairly large percentage of cows.

Sevie Kenyon: What is it? What is mastitis?

Pam Ruegg: So mastitis is a bacterial infection of the udder. We recognize it based, not on finding the point of infection, we can’t see when the cow becomes infected, but we recognized it based on the inflammation that that infection produces.

Sevie Kenyon: What new things are you discovering?

Pam Ruegg: In 2010, we visited 52 dairy farms here in Wisconsin. In this particular study, we went to larger dairy farms. Now, we do lots of studies on small dairy farms but in this study we were targeting farms that had more than 200 cows.

Sevie Kenyon: Why did you do that?

Pam Ruegg: We did that because the management of these farms has been changing dramatically and these farms have had a lot of emphasis on controlling contagious mastitis pathogens. We had quite a bit of evidence that they were being successful in that. Yet, they were still experiencing a lot of clinical symptoms of mastitis on their dairy farms and we wanted to look at some of the pathogens that were causing that, the bacteria, and also some of the management strategies relative to controlling it.

Sevie Kenyon: Were there some surprises in your findings?

Pam Ruegg: There were. What we really found was that the pathogens, the bacteria that are causing mastitis, have changed substantially in the last 10 – 15 years. You know, we ended up with milk samples from about 800 cases of clinical mastitis occurring on these 52 dairy farms that we visited. Now, [of] those cases of mastitis, approximately 80% of them the symptoms were very mild. In fact, in only about 15% – 20% of them did the cow actually have any systemic symptoms of illness. In other words, like a fever or off-feet or something like that. In the rest of the cases, it was either simply slightly abnormal milk or maybe a little bit of a swollen quarter. When we took the milk samples from those cases, our most common finding on what was causing the mastitis is we had a milk sample where no bacteria could be recovered. Farmers don’t like that when they submit a milk sample for culture and it comes back microbiological negative. So we have a cow, she’s got abnormal milk, the farmer recognizes that she has mastitis, we take a milk sample, we take it to the laboratory, and when we look at that plate there’s no bacteria obvious.

Sevie Kenyon: So what’s happening to it? Where is it?

Pam Ruegg: So, most commonly we believe that in most instances what we’re dealing with is what we call opportunistic bacteria. The bacteria out there in the moisture, the mud, manure that the cows udder comes in contact with that simply causes the infection and because these bacteria haven’t evolved to live in the udders of the cows, the cows immune system responds strongly to them and is, in many instances, successful in eliminating them.

Sevie Kenyon: What does this imply for the dairy business?

Pam Ruegg: Then we found that the most common pathogens, the bacteria that we found associated with mastitis, were E. coli, environmental streps, klebsiella, and then a whole host of about 17 or 18 other bacteria, of which many just are present in the environment of the cow and, again, opportunistically causing these infections.

Sevie Kenyon: What do you think has caused this change?

Pam Ruegg: I think a lot of it has to do with changes in the cow and changes in the way we manage the cows. You know, cows are very high producing today. They produce large volumes of milk in relatively short periods of time and to do that they have to milk very rapidly through a relatively small teats sphincter. Those teats sphincters have to open up quite wide to milk fast and so I have some suspicions that they’re not closing as rapidly, perhaps, as they did in the past. At least on some of the cows it may be more susceptible to mastitis infections.

Sevie Kenyon: You also looked at some work with antibiotics. Could you describe that for us?

Pam Ruegg: First of all, we recorded the history of the cow relative to has she been exposed to antibiotics before. And then for many of the bacteria, the Staph aureus, the Streptococci, and the coagulase-negative staph, we checked for resistance to commonly used antibiotics that are used on farms to treat mastitis. It doesn’t appear that there’s an emerging explosion of antibiotic resistance in these bacteria. It does appear that relationships between, for example, penicillin used on dairy farms and resistance to penicillin, are found on some of these farms. In other words, we don’t see an increasing trend of antibiotic resistance but there does seem to be some stable populations of resistance to some type of bugs.

Sevie Kenyon: What advice do you have for dairy producers when dealing with this modern world of mastitis?

Pam Ruegg: It used to be that we would see a case of mastitis and we could make a pretty good bet that it was Staph aureus, Strep Ag, or E. coli. Today all bets are off. Today, what we really need to be doing, kind of the take home message here, is we need to be culturing these cases of mastitis because identifying the type of bacteria will tell us, “Should we use a drug?” and “If we are going to use a drug are we going to use a drug that’s effective for the particular bug?”

Sevie Kenyon: Look into your crystal ball a little bit. What do you see down the road for managing cattle for these diseases?

Pam Ruegg: Yeah, the biggest thing is probably going to be we’re going to have to come out with cheap diagnostic tests that allow us to understand what the bacteria is rapidly. I think those tests will come along, there’s an explosion in diagnostic testing options. The thing that’s kept them from moving into the dairy industry is cost and as the cost comes down I think what we’re going to find is a lot more utility in identifying those bacteria rapidly.

Sevie Kenyon: So Pam, I’m driving down the road listening to this, what does it mean to me?

Pam Ruegg: I think what it means to the consumer is they shouldn’t have to worry about the development of antibiotic resistance because of the use of antibiotics on dairy farms. We don’t see any increased trends for that. I think if you’re a dairy farmer it means that we need to continue to be preventing mastitis and we need to be focusing on understanding what the bacteria are on each farm that causes mastitis.

Sevie Kenyon: We’ve been visiting with Pam Ruegg, Department of Dairy Science, University of Wisconsin Extension in the College of Agricultural and Life Sciences, Madison, WI and I’m Sevie Kenyon.