In the previous issue, we began a series on mastitis with a focus on contagious pathogens. In this issue, our focus will switch to the environmental pathogens and their identification, treatment and control.
As their name suggests, environmental pathogens reside primarily in the environment of the cow in contrast to the contagious pathogens that reside primarily within the udder of infected cows. Bedding, manure, feedstuffs, mud and water are all likely sources of environmental mastitis pathogens. The challenge with environmental organisms lies in the difficulty in eliminating exposure. Whereas strep. agalatiae, staph. and mycoplasma organisms (the primary contagious pathogens) can be greatly reduced or eliminated by treating or culling affected cows, it is impossible to eliminate all pathogens from the environment.
The environmental pathogens are more likely to cause clinical mastitis resulting in abnormal milk, evident disease within the udder and at times severely sick cows. As a group, they generally cause an infection that is shorter in duration and are less likely to become chronic in nature. Bulk tank monitoring and even individual somatic cell counts are often not very effective in identifying infected cows. Instead, abnormal milk may be noticed during pre-stripping or in the case of coliforms, acute and severe clinical disease is common. As with all cases of mastitis, culture is the definitive means of identification and aids in antibiotic selection.
Effective treatment should always include the use of intramammary antibiotic infusion. Several commercial products are labeled for environmental strep. infections and a few have a label claim for E. coli. In cases with severe clinical disease in which the cow is systemically ill, parenteral antibiotics such as oxytetracycline or ceftiofur should be considered in addition to supportive care with IV fluid administration and anti-inflammatory drugs. Often times antibiotics constitute the focus of treatment, however, supportive care is paramount to saving cows with severe clinical disease.
The most important defense against environmental mastitis is prevention. Good udder preparation and milking hygiene including a pre-milking teat dip is important. However, providing a clean environment for the cow is likely the most important aspect of prevention. If cows are lying down in the mud in between milkings environmental mastitis is likely to be a significant concern. Providing a clean, dry bedding or spreading cows out over clean pasture is preferred. Keeping lots and feeding areas cleaned of manure is also important. Treating all quarters of all cows at dry off will help in reducing the number of infections in the early dry period. Furthermore, proper nutrition with focus on vitamins A and E and the trace minerals selenium, zinc and copper will aid in the effective defense by the immune system. Lastly, I would recommend that all dairies consider vaccination against E. coli as a measure to reduce the number and severity of E. coli infections.
Darren Loula, DVM, is owner of Christian County Veterinary Service, LLC, a mobile large animal vet clinic.
