Missouri Dairy Business Update
Volume 3, Number 5
May 2003

For a dairy cow, summer heat stress lasts more than 100 days. Dairy cows do best when it is cool and dry. Summer heat stress begins to show up with a decrease in milk yield when the temperature goes above 75- 80 degrees depending on humidity.

First response to heat stress is an increase in respiration rate. Cows dissipate a significant amount of heat through respiration Liquid water is changed to gas in the lungs. Evidence of increased heat stress is a respiration rate above 60 breaths per minute. At 120 breaths / minute you better take action to cool poor Bessie.

At a body temperature about 102.5 the dairy cow begins to work to cool herself (normal is about 101.5). High producing cows give off a lot of body heat. A single cow will give off 3,000-to 6,000-btu/ hour in the summer. Place 100 of these beasts in a holding pen at watch it warm up!

Things we can do for cow comfort

1. Provide shade with water close by. This is true for grazing dairies as well. Allow 50 square feet per cow for space under the shade. Permanent shades need to be 10-12 feet high. Portable shades with a black nylon mesh cloth need to be at least 8 feet high. Observe available shade in the free stall barn in the afternoon. Free stall barns should be constructed with an East/West orientation so the summer sun doesn't heat the barn as much. Shade over the feed bunk will enhance feed intake.

2. Water. Heat stress can increase water intake by more than 50 percent, from 25 to 40 gallons per day. When grazing, dairy cows will travel to a waterer three to five times per day if they do not have to walk more than 600 to 800 feet. Trough type watering devices should be available. Single hole watering devices limit access. A cow will consume 3 to 5 gallons per day when water is provided on the exit from the milking parlor. (The act of giving milk makes cows thirsty) Research work at Kansas showed adding additional water troughs at the pen exit, middle and end crossovers resulted in water intake increasing over 20%. Water quality is important. Troughs should be cleaned at least weekly. While visiting a dairy in Mississippi with 26,000-lb./per-cow milk yield a scrub brush was observed hanging adjacent to every water trough.

3. Fans. Air passing over a warm cow enhances cooling through evaporation. A minimum guideline is to provide one 36-inch fan for every 30 feet and one 48-inch fan for 40 feet of distance. Fans should be over the free stalls and over the feed bunk. Fans need to be tilted down towards the cows. Bottom of the fan should be no more than 8 feet above the floor. A 3 foot fan, 240 volt, 1/2 horsepower motor will use about $0.03/ hour of electricity. If the fan runs 24 hours/day each fan would cost $0.72/ day. Estimating one fan/ 6 cows (including fans in the holding pen) this would cost $0.12/ cow /day for electricity or about one pound of milk/ cow. Fan cost at $250 lasting 5 years would divide out to $0.08 /cow/day. Total cost is two pounds of milk. Heat stress will usually decrease milk yield 10 to 40 % if relief is not provided.

4. Sprinklers. Research has show the combination of soaking and fans is the most effective way to cool cows. Concept is to thoroughly soak the cow in three minutes. Sprinkler shuts off with the fan cooling the cow by evaporation. Fans run continuously. Sprinklers should be mounted above the feed bunk at a minimum of 7 feet above the floor at 6-8 feet spacing. Adequately sized nozzle should provide 0.5 gallon/minute at 20-25 psi water pressure. A 180-degree nozzle works well at the feed line. This reduces excessive wetting of the feed. Sprinkler pipe should be adequately sized. One inch PVC pipe is suggested for lengths of 0 to 200 feet from the solenoid to the last sprinkler nozzle. The PVC pipe must be supported or excess sagging will result. Newer type nozzles come with a check valve, which prevents emptying the water line between soakings. A response of 100 pounds of milk per cow during the summer is needed to cover the fixed and variable costs of the sprinkling system

Check out the " Heat Stress" page on the " Missouri Dairymen's Resource Guide" website for info.

Think Cool