Because I live in Virginia, I have the joy of experiencing all the fun of winter plus southern summers. Southern summers are characterized by fairly high temperatures (85-100 plus) combined with fairly high humidity (50-100 percent). While we don't get the extreme heat experienced by some western states, I think the humidity levels add an extra layer of information that needs to be considered when conditioning for endurance. It particularly matters to me because I have a big, black, warmblood/draft type horse who probably doesn't cool as efficiently as a smaller, lighter breed.
Last year, I used this rule (which is based on assorted guidelines I've seen in general heat stress articles, but a little different than the standard - I'll explain why in a bit). If the Heat Stress Index (Temperature + Humidity) was:
- Under 130, no worries (Unless the actual temperature was over 90 degrees, then I would take it a little easy).
- Between 130 and 160, take it easy on anything particularly strenuous.
- Between 160 and 180, do mostly walking work and keep dressage schooling to short bursts with frequent breaks.
- Over 180, don't ride.
In terms of using electrolytes for Nimo, I didn't use any commercial products last year because my thinking was that it just didn't seem necessary for rides less than 25 miles. I did add about a half tablespoon of salt to every feeding and to all post-ride mashes (in addition to making sure a salt block was available in the stall and paddock). But, I'm thinking that I'd like to expand that protocol a bit this year. The reason is because I've found that for me, drinking Gatorade (even though it really is not that great of a product due to the high sugar content) makes the difference between feeling fine after a hot ride and feeling like I want to die. And, if it makes that much difference to me, maybe it would make that much difference to my horse.
So, I'm planning to do a little experimenting on my conditioning rides this year. Because I feel best if I drink Gatorade before, during, and after a ride, I'm going to try doing a minimum of a pre- and post-ride mash with electrolytes in it for Nimo. If I can get a during-the-ride mash in for rides longer than 2 hours and where there are opportunities to drink, I'd like to do that too. I don't think I'll start out using a competition level of electrolytes for Nimo. Instead, I'll probably use maybe half as much to start and go from there.
So, to answer my title question...For me, it is too hot to ride if the temperature is over 95, regardless of humidity level. I just don't tolerate heat well, and I don't see any reason to torture myself even if Nimo doesn't mind. I also consider it too hot and humid to ride if the Temperature plus Humidity is over 180 because I think the effort needed to ensure proper hydration and cooling just isn't worth it.