Staphylococcus aureus is a contagious type of bacteria that can spread from cow to cow at the time of milking. Infected cows will have a chronically high somatic cell count, many of which will be ‘millionaires". To make matters worse, it is very difficult to get rid of these bacteria with antibiotic treatment. We, therefore, have to turn our attention to preventing these infections from occurring.
Some basic principles of milking time hygiene need to be emphasized. It is crucial that gloves be worn, and that means clean ones!Staph. aureus can also colonize hands and the use of gloves will help to stop the transmission from humans to cows. If a cow is known to have a Staph. aureus infection, change gloves or spray them off with teat disinfectant after prepping her. This will help to prevent the spread from that cow to the next. Another key factor to remember is the importance of single-use towels. If a towel is used on a Staph. aureus infected cow and then that same towel is used on the next cow in the parlor, the second cow is exposed to the bacteria that is present on the cloth. After milking, there is a residue of milk left in the unit. The next cow to be milked with that unit may be exposed to bacteria present in the residue. Even so, washing units out after a Staph. aureus positive cow is not recommended because it can cause more harm than good. However, the use of an approved postmilking teat dip is suggested to help prevent new infections.
Aside from milking time hygiene, calf management must be considered. Some research suggests that baby calves fed milk containingStaph. aureus can harbor those bacteria until they calve as 2 year olds, at which point it can show up as mastitis. Therefore, if a Staph. aureus infected cow has been identified, it is better to discard her colostrum. This also applies to waste milk. Waste milk can be a great source for all kinds of bacteria and feeding this milk can have the potential of infecting calves with Staph. aureus. Heifers are the future, so their health needs to be protected. A variety of Staph. aureus vaccines have been tested and some have been marketed over the years. Previously developed vaccines focused on antibody production against Staph. aureus with little to no success. Currently, the mastitis lab at Virginia Tech is looking at an alternative approach to vaccination.
The strategy is to target the cells, rather than antibodies, of the immune system. Changing the make-up of the somatic cell count during mastitis may allow the cow to clear infections without use of antibiotics. This may be an effective way of reducing the detrimental effects of Staph. aureus in the long-run. The milk lost from an increase in somatic cell count due to Staph. aureus is tremendous. Therefore, focusing attention on the prevention of these infections is crucial.