Vale Veterinary Group veterinarian and director Andrew Biggs says mastitis treatment needs to be targeted.
In a recent presentation at the British Mastitis Conference, Vale Veterinary Group veterinarian and director Andrew Biggs presented the results of bacteriological tests conducted on 15,194 milk samples between 2014 and 2016. The samples were from cases of clinical mastitis and cows with high somatic cell counts. The analysis looked at the most commonly isolated pathogens found in the milk and how sensitive they were to antibiotics. His results revealed that E. coli showed resistance to routine antibiotics: Ampicillin – 58% sensitive; 10% intermediate; and 31% resistant. For Amoxicillin/Clavulanic acid, 75% were sensitive, 11% intermediate and 14% resistant. Biggs used this study to segue into a more important topic: the prudent use of antibiotics. Mastitis treatment needs to be targeted, he said, and the necessity of antibiotics must be assessed before they are used.
His first point was that antibiotics are of limited benefit in E. coli mastitis cases especially mild ones. “If we do use antibiotic sensitivity testing for an E. coli clinical case it may be useful for that clinical case but it won’t predict antibiotic sensitivity in future cases because that bug came from the manure,” he explained. “There are millions of different strains of E. coli in the environment, so you can’t use the results to predict future resistance patterns.”
“However, if you’ve got potential persistent intramammary infections such as Staphs or Streps (gram-positive, contagious bugs) then it is more likely we will have a few strains on the farm because the new infections are likely to come from another cow. And so antibiotic sensitivity testing on one case can be helpful to predict antibiotic sensitivity patterns in future cases. On a gram-negative basis – because each time it’s coming from the manure to the cow – it’s a random event. It’s not really going to be terribly helpful in terms of predicting.”
With that in mind, Biggs urged attendees to think about the more prudent use of antibiotics. Biggs has been practicing veterinary medicine since 1981, and in that time, a lot has changed. While it’s understandable that older veterinarians would use blanket dry cow therapy in the past, there’s certainly no reason to do it now. Some 30 to 40 years ago, Biggs explained, average national cell counts around the world were as high as 500,000 per ml. If for every 100,000-cell count you’ve got 10% infection in the herd, a cell count that high could mean 50% of the herd was infected.
“Each cow, as it came to drying off, there was probably as much of a risk of it being infected as there wasn’t,” he said. “In other words, there was a justification in treating all animals at dry off with antibiotics because the dry period is a good opportunity to cure intramammary infections and the probability of them being infected was so high.”
“Now, if we have cells counts of 150,000 to 170,000 it’s very hard to stand up in the world and justify treating every cow with antibiotic at drying off because far more of them aren’t infected than are infected,” he continued. “The world has changed in terms of what we’re doing and it’s a question of getting farmers and veterinarians to recognize these changes and not just do what we’ve always done because we think it was right.”
The problem of overuse of antibiotics is not confined to mastitis. For example, said Biggs, farmers who have calves with diarrhea often want to give them antibiotics. “Apart from salmonella or some situations with E.coli in the first couple of weeks of life, there’s very little, if any, evidence that this has any benefit,” he said.
Biggs is of the mind that non-steroidals along with good husbandry and hydration are almost always a better option. “You could almost say any animal that’s unwell should have a non-steroidal. They should only receive antibiotic if there are positive reasons to do so, much like selective dry cow therapy, and it also might have some benefit in that the farmer feels he’s doing something and therefore feels he does not have to give antibiotics,” he said.
Another area where antibiotics are used a lot in agriculture is in the treatment of pneumonia. Biggs wants to see farmers treat calves with non-steroidals as soon as they look “off colour” rather than waiting until they definitely need an antibiotic.
“That brings their temperature down, they stop shivering and shaking, they drink their milk, and they may well get over it on their own,” he said.
The key is good stockmanship and spotting the sick calf as early as possible is key.
But what if it is mastitis? Biggs says you need to get samples into the laboratory so you know what you’re dealing with. “If you build up a picture of what bugs you’re getting then you’ll know what the chances are you need to use antibiotic or not, and if you do, which one is the most appropriate,” he said.
Some farmers, he said, may want to culture their own samples on farm so they can avoid using antibiotic treatment for gram-negative mastitis cases. “However there is a risk that if you do have a significant number of Strep uberis or other gram-positive cases that delay in treatment until you have the result will reduce the efficacy when you do decide to treat with antibiotic,” he said.
One purpose of showing the results of the sensitivity tests was to show that first-line antibiotics work well, so there’s no need to jump to fourth-generation Cephalosporins or Fluoroquinolones. These are considered Critically Important Antibiotics (CIAs) and of high importance to human health. “It’s not just reducing use, but stopping the use of CIAs that don’t need to be used in farm animals,” said Biggs.
“So you can see the E. coli resistance pattern we found, if they’re E. coli clinical cases, there’s a good argument that they don’t even need antibiotics,” Biggs continued. “Maybe as clinicians we shouldn’t be quite so worried about whether they’re resistant or not – that is covered by laboratory surveillance schemes – but we should be diagnosing them better so we know when we don’t even need to use antibiotics thus reducing the pressures driving antimicrobial resistance.”
“And if they become sick then some of those might justify antibiotic, but a lot of E. coli cases don’t,” he concluded.
Currently, antibiotic resistance is not a major clinical issue for veterinarians. It’s more about changing behavior and getting veterinarians and farmers to understand when antibiotics are justified, and when they’re not needed at all.