Last week, I walked all the calves on a dairy in central New York State. They are housed in hutches with collars and tethered at the front of the hutch.
At this time of the year the rear vents are opened. An auto-size tire is slid under the rear of the hutch. The combination of these two adjustments should be to increase air movement through the hutch.
It was a warm day at noon. My recording thermometer read 87 degrees F sitting on a bale of straw sitting in an unused hutch. Thus, some air movement inside hutches would be helpful.
However, when is a vent not a vent?
When the person(s) bedding hutches places too much bedding too far back in the hutch. Many of the hutches were bedded well - the combination of long wheat straw and sawdust was placed far enough forward in the hutch to leave the base at the rear open for air entry.