Current Progressive Dairy digital edition

Ask a Vet: How to handle heat stress

Larry Judge for Progressive Dairyman Published on 24 May 2018
Cows at feedbunk

Heat stress is created when livestock cannot expel enough heat to maintain their core body temperature for optimal production and health. The temperature-humidity index (THI) is a number that combines humidity and temperature to correlate with the amount of heat stress an animal experiences.

Research from the University of Arizona suggests cows experience a milk loss starting at a THI of 68ºF.




A heat stress study found cows suffering from heat stress experience the following:

  • 4,000-pound decrease in milk production per lactation
  • 60-day increase in average days open
  • Nearly 2 percent increase in death loss

For a 1,000-cow dairy, these losses could easily exceed $300,000 per year.


Professor Jodie Pennington at the University of Arkansas recommends testing the rectal temperatures of 10 cows. If seven cows have a temperature of 103ºF or above, your herd is experiencing heat stress. Watch your cows for the following indicators of heat stress:

  • Respiratory rate greater than 100 breaths per minute

  • Excessive salivation

  • Open-mouth breathing

  • Decrease in dry matter intake (A 10 percent decrease indicates the animal is under high stress; a 25 percent decrease indicates severe stress.)


  • Keep cows comfortable and cool.

  • Supply adequate, fresh, clean water at all times.

  • Provide shade, fans, misters (in low-humidity areas) and coolers.

  • Make sure fans are provided near sprinklers for proper evaporative cooling.

  • Deliver feed more frequently and push up feed more often.

  • Feed during cooler times of the day.

Nutritional recommendations

Heat stress has a significant effect on rumen pH. Consider the following to prevent rumen acidosis:

  • Offer high-energy, palatable diets with high-quality forages.

  • Supplement free-choice bicarbonate.

  • Limit crude protein to 16 percent.

  • Keep ration-degradable protein at less than 61 percent.

  • Provide probiotics like yeast and beneficial bacteria which are shown to improve feed efficiency during heat stress.


Take the following steps to treat animals suffering from heat stress:


  • Provide a constant supply of cool water for animals to drink to aid in the recovery process.

  • Add oral electrolytes to the water to ensure adequate hydration.  end mark

PHOTO: Cows at the feedbunk. Staff photo.

Dr. Larry Judge
  • Dr. Larry Judge

  • Veterinarian
  • Animart Professional Services
  • Email Dr. Larry Judge