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Summer Kicks Up Somatic Cell Counts

Chuck Schwartau

Dairy operators tend to think about the winter as being a stressful time for themselves and their cows. While working in the cold may not be a lot of fun for humans, the ability to manufacture milk in the summer heat is a lot of work and not much fun for the cows.

Most dairy operators look at summer heat as a problem for feed intake and cow comfort. But the summer heat also tends to drive the somatic cell count (SCC) up in most herds. Why is that? There are probably many underlying causes, but here are a few that are worth considering.

In the Midwest, high heat usually means relatively high humidity as well. When the humidity is high, evaporation slows way down so barn alleys and other surfaces tend to be wet longer. Alleys in freestall barns generally will never get dry. The cows are walking on wet floors with a certain amount of manure present and, therefore, their feet are always a bit more on the dirty side. Then when the cows lie down, those wet rear hooves come in contact with the teat ends providing a source of contamination. On many farms sprinkler systems are used over the feed alley to help cool the cows, contributing to even more moisture exposure. The result of all this moisture is a greater opportunity to introduce bacteria to the teat of the dairy cow causing a potential for higher SCC.

The lack of these drying conditions extends to the freestalls as well. Regardless of the bedding material used in the stalls, it will most likely be higher in moisture during humid summer weather, creating a ripe breeding ground for environmental bacteria that cause mastitis. In addition, there is some thought that the heat stress on the cow itself may actually lower her resistance and ability to fight off low level infections in the udder. Florida research suggested the summer SCC increase may actually be related to decreased milk production when cows are experiencing heat stress (Shearer and Beede, 1990). Other research, however, suggest the real culprit in the summer is the increased rate at which pathogens multiply, thereby increasing the potential for infection, mainly from environmental pathogens (Hogan et al 1989).

So What Do I Do?

There is no one answer to this question, but rather a series of actions is needed to help keep potential infections in check and, thus, keep SCC in line as well. Remember:

For more information on maintaining milk quality, refer to the University of Minnesota Dairy Extension webpage at and click on the "Quality Count$" link.

Published in Dairy Star June 18, 2005
