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Extension > Extension County Offices > Stearns > County Agriculture Educator > Articles > Heat Stress: Understand Its Impact and Prevent It On Your Dairy Farm

Heat Stress: Understand Its Impact and Prevent It On Your Dairy Farm

University of Minnesota Extension, Stearns County News
June 18, 2014        
           
Source:  Emily Wilmes, Extension Educator-Livestock
University of Minnesota Extension
Stearns, Benton & Morrison Counties


Heat Stress: Understand Its Impact and Prevent It On Your Dairy Farm
By Emily Wilmes, University of Minnesota Extension

ST. CLOUD, Minn. (06/18/14) — Where has time gone?!  Are we really halfway through June already?!  It seems like only yesterday I was talking about cold stress, and now it’s time to talk about heat stress already.  Heat abatement and preventing heat stress on a dairy farm seems easy enough, but there are so many things to keep in mind!  Let’s take some time to review.

Thinking about heat stress is important as it can have a huge economic impact.  The three main heat stress symptoms driving economic loss are:

  • Decreased dry matter intake. Dairy cattle will significantly decrease dry matter intake during heat stress in an attempt to reduce heat production from the digestion and metabolism of nutrients. It is important to develop a nutrient-dense ration during periods of heat stress.
  • Low milk production. Milk production can be significantly reduced during heat stress. A paper titled "Quantifying Heat Stress and Its Impact on Metabolism and Performance" indicated that when cows experience days where the THI (temperature humidity index) is between 65 and 73, milk yield loss averages 5 pounds per cow per day.  According to this projection, during a summer in which the THI reaches these levels for 30 days, lost milk income from a 150-cow herd can add up to as much as $3,375 per year, based on $15 per cwt.
  • Impaired reproduction. Heat stress hinders reproductive performance of the dairy cow and consequential impacts can be seen for months following the exposure. Decreased fertility can lead to more days open and disrupt the cycle to which a cow enters and exits the milking herd.  In addition, embryo loss is 3.7 times more likely in times of heat stress. A single cow's pregnancy is worth an average of $450; however, this value can vary based on a cow's age, future production potential and days-in-milk.

In order to prevent high economic losses during summer, there are several steps that can be taken.  Always keep in mind that cows feel discomfort in the heat a lot sooner than we do.  Cows are most comfortable at 50°F, and begin to feel heat stress at 68°F.  Traditionally, the threshold has been 72°F, but that standard was set decades ago and dairy cows today are more productive and thus more sensitive to heat.  With this in mind, make sure fans and sprinklers are being turned on at an adequate time.  Research suggests fans should be turned on at 65°F.

There are a lot of facilities-related components that go into heat abatement.  Think like an engineer to make sure you don’t miss anything.  Kevin Janni, Agricultural Engineer with University of Minnesota Extension provides his facilities tips:

  • Shade cuts solar heat gain for cows on pasture. Cows in barns have shade. Roof overhangs provide more shade near the barn sidewalls.
  • Barn ventilation cools cows by providing air exchange between inside and outside. Ventilation can be by either natural or mechanical means. In hot weather, provide as much ventilation as you can.
  • Tunnel ventilation brings air in at one end or side of a barn and exhausts it out the other. Size fans and inlets correctly and make sure the fans are well maintained and inlets are open.
  • Mixing fans hung from rafters or trusses create air movement during hot weather to help cool cows by blowing air past the cows. Mixing fans do not provide air exchange between inside and outside but they supplement the cooling effect of ventilation.
  • Low pressure sprinklers along feed bunks or in holding areas wet the cows’ backs to provide cooling. Wet the cows’ backs to the skin. Low pressure sprinkler systems must turn on and off. Cow heat evaporates the water and cools the cows when the sprinklers are off.  Mixing fans enhance the effect.  At 70°F sprinklers should be turned on at a cycle of 2 minutes every 15 minutes.  As temperature increases, sprinklers need to cycle at shorter intervals.
  • High pressure misters cool the air by creating a fine mist or small droplets. The droplets need to evaporate before they hit the stalls or bedding. Place misters near inlets. Misters are not as effective when ventilation blows the mist out of the barn before the air cools.
  • Evaporative pads cool and humidify the inlet air in low-profile cross-ventilated barns. The pads need to be uniformly moist for best effect. Fresh water needs to be added, and check for mineral accumulation and algae growth.

As always, and especially in summer, cows need plenty of access to fresh water.  There should be 1.2-3.6 linear inches of space per cow at a waterer.  As temperatures increase, so does water consumption and crowding at waterers can occur.  Ensure you have enough space at each waterer, as well as enough waterers.  In freestall barns with 4 rows, waterers at every crossover are adequate.  Understanding barn and pen design, as well as stocking rates will allow you to make the right decisions when it comes to waterers.  Also, think about having a waterer just outside the parlor.  Cows consume about 10% of their daily water after milking. 

There are a lot of components to keeping cows cool and reducing economic impact in the summer.  Prepare for the dog days of summer now by checking all fans, sprinklers, and waterers to make sure they are working properly.

If you have any additional questions about heat stress or heat abatement, call me at the Stearns County Extension Office at 320-255-6169.

Contacts

Emily Krekelberg
Extension Educator, Ag Production Systems - Livestock
(320) 255-6169
krek0033@umn.edu
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