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Newsletter of Penn Dutch Cow Care July 2012

Hi Folks,

I’ve found over the years that the weather around July 4th somewhat predicts what it will be like the rest of the summer. It’s hot. Heat stress comes to mind. Fortunately over the past 15 years it seems that most farmers have taken appropriate measures to keep cows more comfortable during hot weather.

An on-line article called Heat Stress in Dairy Cows, a team of U. of Arkansas authors provides good information http://www.extension.org/pages/11047/heat-stress-in-dairy-cattle#Signs_of_Heat_Stress

Table 1. Relative changes in expected dry matter (DMI) and milk yield and water intake with increasing environmental temperature.


Expected intakes and milk yields



Milk yield

Water intake

























Sources: National Research Council. 1981. Effect of Environment on Nutrient Requirements of Domestic Animals. National Academy Press, Washington, D.C. Dr. Joe West, Extension Dairy Specialist, University of Georgia.

Notice this is information is from the National Research Council in 1981. Information like this doesn’t change.  With increasing heat, cows eat less, milk less and need more water - it’s that simple. Cows need - and will drink - 30 gallons of water a day!

Signs of heat stress are very consistent among animals, it’s just that some are more at risk than others: those that are clinically ill and those teetering on becoming ill and especially those right around calving time.

Typical signs include the ones shown in the table above - and also standing more and seeking shade. Once increased breathing rates are seen, more severe heat stress is setting in. If cows are open mouth panting, immediate action is required or heat stroke is likely.

It should be remembered that while pasture and grazing is a great goal for healthy cows, the hottest days of summer are NOT times for dairy cows to be on pasture (they won’t graze if too hot anyway). If cows are waiting at the gate and looking to the barn, they want to come in. Do something, don’t let them just stand there.

Some of the nicest barns on the nastiest, hottest days are those with tunnel ventilation. I was in one today on an organic farm where it almost was difficult to walk upstream into the wind generated by the fans. The cows looked content and calm. Grazing at night is certainly allowed. Cows will graze much better in the early morning and cooler evenings than during bright daylight hours when it’s steaming. Simply put, cows shouldn’t be on pasture between 11am - 5pm on those hot and humid days above 90 degrees. 

Individual cows or young stock that seem dull and have a distant look – and especially if breathing rapidly and shallowly – are likely suffering from heat stroke and need to be hosed down immediately. A cow with heat stroke usually appreciates being hosed down and will stand there without being tied. A cow with a temperature of 108 will usually drop to about 103 with about 20 minutes of hosing. Animals with temperatures of 109 or higher usually get permanent brain damage and won’t recover fully. If a hose isn’t available, pouring water over the animal (especially the head, but everywhere also) will take many 5 gallon buckets to be effective. Those animals that already are having problems – like a fresh cow that had twins and didn’t clean, or an animal which had pneumonia as a calf, or scouring calves – will all be more likely to succumb to real heat stroke if not kept cool somehow. Hint: put a cinder block under the back of calf hutches to prop them up and allow air to circulate better through them.

Note – if a cow just freshened and has both milk fever and heat stroke, treat for the milk fever first (give a bottle of IV CMPK) to help get her up and then use water to cool and for her to drink.

While there’s not much you can do about the hot summer weather, there are things you can do to prevent them from getting heat stroke. More and more people are misting their cows to cool them. And while I don’t think cows in streams is generally a good idea, on those hottest days it seems reasonable to let them enjoy some swimming time, just as we like to do. Allowing cows into the woods is another option. But making them wait at the gate until milking time to come in from a baking pasture is simply being foolish.

What do you do to keep your animals more comfortable during times of heat stress?

For Bovinity Health, information on functional alternatives to antibiotics see:

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