Chuck Schwartau, Regional Extension Educator – Livestock

June 18, 2005

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:

• Just because it is summer, this is no time to slack off on alley and stall maintenance. Be sure to scrape alleys often, keeping the accumulated manure to a minimum. This, in turn, keeps manure on the cows’ feet to a minimum.
• Regular dressing of the stall bedding is important. Scraping the inevitable manure off the stall platform and keeping clean, dry bedding material near the back helps keep clean udders.
• Take advantage of air movement in barns that help keep cows cool and help dry their environment. Free air movement from open-sided barns and properly placed fans can reduce the moisture level in the stalls and help dry some of the alleyways as well. That will help keep cleaner feet and cleaner cows.
• If there is the opportunity to let cows out on dirt exercise lots or pastures, it will give them some time on dry surfaces and reduce the manure deposited in the alleys. This might actually allow some alleys to dry. An added benefit to this practice may be healthier feet and legs because the cows are off the concrete for a few hours.
• Make sure the milking routine and equipment are kept at their highest quality level. If cows are carrying even subclinical levels of infection, extra steps need to be taken to prevent contamination of other cows thru poor milking practices. This includes the need for thorough teat dipping of all quarters.
• Move cows around the barn and parlor slowly. Fast moving cows kick up more manure onto their feet and legs. Cows moved calmly are also more likely to enter the parlor smoothly. This will help them more readily enter the milk letdown phase of the milking process.

For more information on maintaining milk quality, refer to the University of Minnesota Dairy Extension webpage at www.extension.umn.edu/dairy and click on the “Quality Count$” link.

Clean feet and legs help keep somatic cell counts lower.