A Different Look at Somatic Cell Count Control
In the dairy industry, it has long been considered that both clinical and subclinical mastitis infections could be divided into contagious and environmental based on the source of infecting organisms. However, control programs, such as the National Mastitis Council's 5-point plan, have primarily targeted the contagious category. Recent data from DHIA cell counts and mastitis culture labs suggests that contagious organisms probably account for 10-15% of new infections. It appears that over the years with emphasis on and better control of contagious mastitis, the infection patterns have changed, and in many herds environmental mastitis organisms are the primary cause of infections and high somatic cell count (SCC).
As a result, it would be of benefit for dairy producers and those working with producers in trying to control or decrease SCC levels on farms to put an increased emphasis on finding ways to better monitor and manage the environmental mastitis organisms. Control of environmental mastitis is especially difficult because it involves careful attention to sanitation, especially teat cleaning during the milking process. Basically, every teat must be clean and dry at every milking. On today's dairies with rapid throughput and milkers working long shifts, this becomes difficult. Frequent feedback on the job milkers are doing is needed to allow them to know if the cow prep is adequate.
It has been repeatedly shown through research that, especially for environmental organisms, the infection rate correlates directly with the degree of bacterial contamination of the teats at the time the milking machine is attached. At this point, the number of organisms left on the teat is what got on since the last milking minus what was not taken off during the cow prep process.
Measuring the degree of teat contamination can be done by differentially culturing the bulk tank milk because the milking process tends to wash the teats and add these organisms to the bulk tank milk. To be effective, this type of monitoring needs to be done on a continual and timely basis so milkers and managers know how well the cows are being cleaned prior to milking unit attachment. The complexity, logistics and cost of the standard bulk tank cultures have limited their usage and delayed the feedback process so that it has not been used effectively as a management tool. There are also numerous observations that show if environmental Strep levels can be continually kept below about 400 and Coliforms below about 100 in the bulk tank milk, the level of environmental mastitis declines and remains at a low level.
Now, there is a solution to the cost and logistics issues for using bulk tank cultures on a more regular basis. A simplified screening method has recently been developed by the Laboratory for Udder Health at the University of Minnesota diagnostic laboratory. This system can be used by individuals with little training and can be used in local milk receiving plants, veterinary clinics or even as an on-farm culture system. It involves the use of special differential media, which is inoculated with a standard cotton swab on a culture plate divided into two equal compartments. After incubation, the colonies on each side of the plate can be counted and if more than 50 colonies are present on the Strep side or more than 10 on the Coliform side, this is an indication there are too many colonies and attention to management and milking procedures at the dairy farm is needed. Milk line sampling can also be used to make the evaluation more specific such as for a milking shift or a string of cows. A dilution process can also be used if it is desired to determine the number of organisms more precisely in the case of higher organism numbers.
It is important to remember that environmental mastitis is a disease that can be controlled. However, the dairy manager and employees must take the appropriate steps in sanitation and/or all the milkers need to have consistent pre-milking teat end cleanliness. It also means keeping cows as clean as possible and avoiding over crowding in the housing facility.
The use of this new simplified, more versatile bulk tank culture monitoring system on a regular basis can be a significant tool for the dairy farm in the battle to control somatic cell and clinical mastitis due to environmental sources.
For further information,view the "Minnesota Easy Culture Environmental Monitoring System" PDF; or contact one of us at the Laboratory for Udder Health, phone: 612-625-7053 or toll free at 1-800-605-8787 or e-mail firstname.lastname@example.org.
Drs. Bey (left) and Farnsworth at the U of M Laboratory for Udder Health showing a culture plate used to count colonies of Strep and Coliform bacteria after incubation.
Published in Dairy Star March 10, 2007