There is very little hard data that indicates exactly when a calf will become heat stressed. Industry consensus estimates heat stress occurs between 78 to 80° F in calves. When temperatures rise above 78°F the calf begins to sweat and respiration rates increase.

Consequences of increased respiration rates and sweating are rapid dehydration, reduced feed intake, a weaker immune system and the internal body temperature of the calf rises – which is never good. In addition, the calf will burn more energy as it tries to drive heat from its body and it is likely that fewer of the nutrients that are consumed will be put toward growth. Heat stressed calves also are more likely to have a slower rate of gain, which means they might not reach breeding size in a timely manner. As a result, age at first calving could be pushed back. If a calf becomes too stressed from heat, it can die.

Tom Earleywine, technical services director for Land O’Lakes Animal Milk Products Co., offers these tips to help calves cope with heat stress:

  • Evaluate milk replacer formulas. Be sure to provide a high level of nutrition to calves so they can grow to their fullpotential and meet their energy needs as they struggle to relieve heat stress. Transitioning to a calf milk replacer formulated for warm weather can result in greater feed efficiency and bottom line potential. New milk replacer formulas provide the optimal protein-to-energy balance as temperatures moderate and are designed to meet the specific needs of the calf.
  • Consider adding a third feeding of milk replacer. Research shows that calves fed three times a day show optimal growth, better feed efficiency, consume more starter prior to weaning and have greater chance of survival to lactation than calves fed twice daily.
  • Provide free choice electrolytes. High-quality electrolytes with suspension agent mixed properly can be free choice fed during heat stress.
  • Offer free choice water. Empty and refill water pails several times throughout the day to offer fresh water. It is typical for calves to double their water intake during periods of intense heat. Switching to five-gallon pails also may be helpful.
  • Clean and sanitize water and milk pails frequently. Warm weather promotes algae, mold and bacteria growth. Keeping water and milk pails clean and sanitized will help keep these populations down, as well as help control fly population.
  • Keep calf starter fresh. Calf starters can go bad in hot weather, so it’s important to make sure the feed is kept fresh. Note that molasses, a common calf starter ingredient to aid in palatability, can be a tasty attractant for fly populations. Newer calf starters use alternative natural palatability enhancers with minimal molasses.
  • Provide shade. Make sure to provide calves plenty of shade in hot weather.
  • Evaluate calf handling. Consider changing the time of day when handling calves is done. Routines that were fine for cold weather might not be the best for the calf in warm weather.
  • Get a handle on flies. Unfortunately calves are a hot spot for flies. Using a milk replacer and a calf starter that includes a feed-through larvicide can help to keep the fly population down. A reduced fly population can help reduce stress to the calf and the spread of diseases by flies.