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Virginia Cooperative Extension - Knowledge for the CommonWealth

It's summer time! Are your cows cool?

Dairy Pipeline: July 2004

Sue Puffenbarger
Extension Area Dairy Agent,
Franklin County
(540) 483-5161 email:

We all know the effects of heat stress: reduced DMI, reduced milk production, decreased reproductive performance and the list goes on an on. How do you know your cows are heat stressed? Rectal temperatures will be above 102.5 degrees; respiratory rates increase to 80 breaths per minute (from 50 to 60) and the things that most people notice, milk production and DMI decreases at least 10%. Preparations for relieving summer heat stress should have been initiated in March, but there are many things that you can do now to help remedy the situation. Water is the number one limiting factors on dairies, so you need to provide plenty of fresh, cool water. Cows need 3 to 4 linear inches of space at the water trough to prevent boss cows from restricting access of other cows to the troughs. In the summer, water intake will increase from 30 gals/cow/day to 50-60 gals/cow/day. It should also be available to cows immediately after they exit the parlor. The process of milking causes cows to be thirsty and you need to take advantage of that to maximize water intake. One low cost way to increase the amount of water space on your farm is to install PVC pipe waterers along fence lines and lanes. To do this you will need a large diameter PVC pipe with the top third cut off along the horizontal access. Cap the ends, add a float, and you have a durable watering system that was easy and cheap to install. To make it easy to maintain, add a handle and attach the pipe in such a way that you can easily tilt it to dump the water and debris. One thing to be sure of is that you have a water line that is large enough to maintain at least 50% water volume during the highest time of water demand. Another area to consider when trying to alleviate heat stress, do you clean your fans? Most people don't think of it, but dirt on fan guards can reduce airflow by as much as 40%. How about placement? Thirty-six inch fans need to be placed every 30 feet and 46 inch fans every 40 feet. By doing this, you eliminate dead space under the fan next in line. Fans should be placed at a 30-degree angle for optimum cow contact. A good way to check if your fans are working properly and placed correctly is to measure wind speed. If you are standing directly under a fan in a line of fans, wind speed at chest level should measure at least 5 mph. If that is not occurring you either need to clean your fans, check their placement or check the air flow rating (cubic feet per minute, the fan may not mechanically be able to move enough air to do what you need). When targeting areas for cow cooling, the holding area should be the first to be considered. Limit the amount of time spent in the holding pen, especially in the summer time, to about an hour to an hour and a half. In one group herds, try holding back half of the herd at the feed bunk or the freestalls where hopefully heat stress is less. Ideally, you should have fans or a sprinkler system in the holding area to help reduce heat stress. If you can't put a sprinkler system in the holding area, try adding a soaking station as the cows exit the parlor. To do this you need two showerheads aimed at a 45-degree angle opposite each other and something to turn the system on and off such as an electronic eye or wand system. This soaks the cows and allows for evaporative cooling. With the volatility of milk prices, we need to do everything possible to maintain production. These are just a few things that you can still do now to minimize your loss of milk production before the summer heat becomes worse.

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