Dairy Calves Feel the Heat Too

With summer right around the corner comes higher temperatures and humidity.  Our management focus turns to managing heat stress in the cows.  We know from research heat stress has dramatic effects on milk production, which affects the farm both in cow health and the pocketbook.  But what about the youngest members of the farms, the calves?

Young calves and heifers may be more tolerant than milk cows when it comes to heat, but heat stress can still have negative effects.  Calves grow best in temperatures ranging from 55 – 78 degrees F.  In this range of temperatures, the thermal neutral zone, calves can maintain a constant body temperature regardless of the outside temperature without expanding extra energy.

When we think about environmental stressors, we tend to think about cold stress.  Anytime the outside temperature falls below 55 degrees F, calves begin to use extra energy to stay warm and maintain its body temperature.  The same is true for temperatures above 78 degrees F, calves use energy to cool the body and maintain its body temperature.  Above 78 degrees F there is a potential for heat stress, but much depends on humidity and radiation.  Heat stress occurs when high ambient temperature, high relative humidity and excessive radiant energy that prevents heat loss by animals.

Calves usually are able to adjust to higher temperatures but this comes at a cost in the form of reduced growth rates.  Heat stress in calves will increase dehydration, reduce feed intake and lower the immune system.  The calf energy needs also increase during times of heat stress.  The nutrients consumed during this time are utilized by the calf to cool its body, rather than for growth.  Because of reduced weight gains, there is the potential for calves to take longer to wean, post-pone first breeding and staying in the replacement herd longer.  At an average of 42.77 per day to raise a calf from the time it is moved to group housing to the time it freshened, it adds up quickly financially when it takes longer to add the heifer to the milking herd.

Just as in cows, the typical signs of heat stress in calves include increased respiratory rates, heavy breathing, increased body temperature, poor appetites, and reduced movement are showing typical signs of heat stress.

Follow these strategies to help calves beat the heat this summer:

  • Provide shade, reduce exposure to direct sunlight.  Providing shade reduces the temperatures inside hutches.  It also lowers calf body temperatures and respiration rate.  If no shade is available, provide a shade cloth over the hutches while providing enough height for workers to walk under and allow natural air flow.
  • Move more air.  Improved air flow is a basic need for all housing systems.  For calves housed in barns, air flow rates for calves up to 2 months of age are 50 cfm under mild conditions and 100 cfm (40 air changes per hour) under hot conditions.  Elevating the rear of calf hutches six to eight inches improves air flow and reduces bacterial contamination.
  • Offer plenty of clean, fresh water.  As calves attempt to maintain their body temperatures, water is lost through increased respiration and evaporative cooling (sweating).  Calves need plenty of water to replenish the water lost to cooling.
  • Keep grain fresh.  Calves will naturally eat less grain during heat stress.  Encourage eating of starter by keeping it fresh.
  • Increase liquid feed offered.  During times of heat stress calves use more energy to cool it’s body.  Calves may not eat as much grain during this time, but generally don’t refuse milk replacers if an extra amount is offered.
  • Consider inorganic bedding.  Sand is a poor insulator and does not retain heat.  Sand also helps to control flies.  Sawdust is better than straw for summer bedding.
  • Work calves (pen moves, vaccinations, etc.) during cooler hours of the day (i.e. morning).  Make sure calves are handled gently and properly.
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