Training in the hot summer

We've arrived at the summer solstice - - the longest day of the year.  From now on, the shadows will start to lengthen, but the average daily temperatures will continue to increase since they follow with a lag.  Training days will be hot and vigilance will be needed to protect the dogs in their exertions.

The rule of 140 (temperature + relative humidity) is sometimes cited as an indicator of danger for exercising dogs.  I'm not sure if there is a better rule out there, and maybe the rule of 140 serves simply as a reminder.  In the south, it is easy to get to 140 (70 degrees, 70% humidity) before dawn.  Ice, water, fans are all necessary training tools.  An early start and finish are helpful.  It can be sticky humid in the grass for the dogs.

And, when the dogs come off the field, stake them out.  Don't kennel them until they have a chance to cool down in the grass and breeze.  That battery-powered Ryobi fan and a stake-out cable in the cool shade should do it.

Below I traced the rule of 140 onto NOAA's Heat Index just to see if there was any basis for the rule.  Too bad NOAA's Heat Index does not continue down to 50 degrees, the temperature above which heat is a consideration for an active dog.  The rule of 140 does not track neatly with the heat index, since the Heat Index ranges from 82 to 109!  Why would that be?  Shouldn't the rule of 140 and/or the Heat Index  express the BTUs in the atmosphere at different temperature/humidity combinations?

We've often run the dogs in the Heat Index range of the upper 80's and low 90's.  The Mazomanie, WI Hunt Test last July was probably in the mid 90's F and 70% humidity.  The dogs were kept to short turns.  In our training, we keep the turns short, and have plenty of water & ice.