Farmers Have Their Say – Q & A

Farmers Have Their Say – Q & A

Many research questions were submitted in the Have Your Say campaign. When possible, the Cluster team forwards some of the questions to Canadian scientific experts working in the area. An example of a question and answer exchange on mastitis follows:

Question from an Ontario dairy farmer about a dairy farm issue

Why are the drugs we’re using to treat diseases like mastitis not as effective?

Answer from Dr. Simon Dufour,

Professor, Department of Pathology and Microbiology, Faculty of Veterinary Medicine, University of Montreal and Scientific Director of the Canadian Bovine Mastitis and Milk Quality Research Network

“This is a very short question, but it requires a very long answer! There are 2 main problems with antibiotic treatment of intra-mammary infections:

First is the mastitis pathogens. These are, in general, extremely specialized in invading and persisting in the mammary gland. To achieve this, they have developed all sorts of mechanisms that help them persist and evade the immune system and antibiotic treatments. Some can penetrate and hide inside the immune cells that are responsible for detecting and killing them. Could you think of any better strategy? The cow’s immune system cannot ‘’seek and destroy’’ them anymore and they are also protected from antibiotics (which do not readily penetrate immune cells). Others can switch to a latent form (like an opossum pretending that he his dead), so that the immune system will not be concerned about them anymore (it’s only dead bacteria after all) and they won’t be affected by antibiotics, which often aim at interrupting vital bacterial functions (in this latent form, bacteria are more or less frozen in time, like Walt Disney or Han Solo, and they don’t have to maintain vital functions). When conditions are favorable (i.e. when the antibiotic is gone) bacteria can migrate back out of the cells or come back from their latent form and cause problems again. Finally, others are resistant to specific antibiotics (sometimes too many antibiotics actually; i.e. multi-resistance). So bacteria have many tricks and they usually use them concurrently to achieve survival in the mammary gland. To defeat them, both a strong immune system and an appropriate antibiotic treatment are required and sometimes it is still not enough.

The second problem is the difficulty for most antibiotics to achieve high concentration in the mammary gland and/or to “reach” all the bugs hiding in the different infected areas. The inside of a mammary gland is more or less like a grape. When administering a tube of antibiotics intra-mammary, especially in a high producing cow, it can be difficult to achieve a good concentration in all parts of the mammary gland. If infection persists in a focal zone, it can later spread back to the whole gland. To make the mater worse, many of the antibiotics that we could possibly administer in the vein or muscle (to circumvent this problem), don’t migrate well into the mammary gland (i.e. concentrations will be high and sufficient in the blood, but relatively lower in the milk).

This is the mastitis puzzle… And this is why, for this disease, prevention is so important.”

Leave a Reply