Expert’s corner: Mitigating heat stress in youngstock

By Dr. Bethany Dado-Senn, Vita Plus dairy calf and heifer specialist
I’m an avid dairy science podcast subscriber. One of my most recent listens was an episode discussing extreme heat stress in lactating dairy cows. Late in the episode, one of the experts noted that, although cooling cows seems relatively straightforward, he is continuously surprised at the never-ending and novel concerns surrounding dairy cattle heat stress.

I couldn’t agree more.

In my (slightly biased) opinion, the latest concern and next frontier for dairy cattle environmental management is the mitigation of heat stress in youngstock. Although dairy calves and heifers are more thermotolerant relative to mature, lactating cows, they are still susceptible to heat stress. This has been particularly apparent the past few weeks as most of the Midwest has seen multiple heat waves. If you’re looking to provide heat stress abatement to your calves or heifers, here are a few options you might consider.

1. Shade
Shade, provided in natural or artificial forms, is essentially the most inexpensive and easily adopted form of heat abatement. It can reduce cattle total heat load by 30% to 50% through protection from solar radiation, leading to decreased rectal temperatures and respiration rates and, in some cases, improved starter intake and growth.

• Natural shade (tree blockage): A good option for pasture-raised heifers
• Artificial shade (shade clothes): A good option for pasture-raised heifers or outdoor hutch-housed calves
  • While a calf hutch alone protects from solar radiation, its design can act essentially like an oven, leading to an elevated microclimate inside the hutch. Providing that supplemental shade over the hutch can reduce air temperatures and solar radiation both inside and outside the hutch.
  • General recommendations for shade structures include providing 3.5 to 6.5 square meters of shade per head and using a material that provides at least 60% to 80% shade block. Consider shade orientation and location depending on time of year and housing designs.

2. Calf hutch adaptations
More recently, dairy farmers have explored alternative adaptations to hutches, such as reflective hutch covers or hutch orientation. Research around these methods reports conflicting results; overall, they seem to have some benefit in cooling calves with no improvements in weight gains.

3. Passive or mechanical ventilation
In addition to improving air quality, passive and/or active ventilation can also promote heat abatement in the summer months. There are a few considerations to achieve proper ventilation for dairy calves.

• Passive ventilation: (open curtains, hutch window kits, prop up the rear of hutches):  A good option for essentially any type of calf/heifer housing
  • In general, a good window kit system or hutch propping will provide air speeds of around 0.33 miles per hour. These air speeds can improve calf thermoregulation and welfare, but have not been shown to positively influence productive outcomes.
  • Keep a close eye on curtain heights during variable springtime weather to ensure good air quality and proper barn air temperatures.
• Active ventilation (fans or positive-pressure tubing):  Good option for indoor individual- or group-housed calves
  • There is not a lot of research regarding necessity or optimization of fan usage for calves. However, providing fans with output air speeds of about 4.5 miles per hour in warmer climates (such as the southeastern U.S.) promotes calf behavior, feed intake and health outcomes.

Tackling this next frontier of dairy youngstock management in an ever-changing environment seems daunting, but, fortunately, we have relatively simple and easy-to-implement tools at our fingertips. Finding the right system that works for your calves and calf team may take some troubleshooting, but, at the end of the day, your heat mitigation strategies should effectively and affordably promote calf comfort and growth across the summer months.