Like TBeventer, I live in AZ, but in the “high” desert, a mile high. I now drive combined driving with a 33″ VSE and a 13.3 mustang pony, but rode 3-day for decades in the USA, England and Ireland.
Getting and keeping conditioned in AZ is always a challenge:
In the preseason, coats are long, weather is cold and sweating is not a good thing, since I don’t have a barn. The VSE grows a coat nearly 4′ long and both the VSE and the mustang have heavy, dense undercoats. Normally I would clip trace or hunter style, but until we finally find our “real” house with a barn, clipping is very limited.
During the competitive season, our driving group holds a series, which begins in “the south”, while it is cool, moves north as southern AZ gets quite warm, and then has sort of a middling competition toward the end, when the north gets frosty.
Obviously, getting the northern horses – with their coats still on, and who have been working in freezing wind, often snow or ice, or just high, cold climate – down south to 60s or 70s weather and having them work the same is as complicated as getting the northern horses with little to clipped coats up the hill! But like TBeventer, we all compete in weather changes. Also, since AZ only has 1 CDE per year, competitors have to travel to warm and sunny CA, NM, TX, OR and WA -all big climate and altitude changes.
Also, at one point I moved to IL where the weather dips to the -20s, wind chills to even colder. The barn I worked was chronically dealing with upper respiratory problems in the winter and tie ups in the summer, where it would get into the 90s with 90% humidity. Horses sweating while standing in stalls!
The first thing I changed was to cancel lessons when the weather dropped below freezing. The barn and indoor schools would be somewhat warmer than that, and some horses would be unworked even then, if they were more susceptible to upper respiratory issues. The biggest difference was that water was unfrozen all night, horses were drinking better than at lower temps, shivering was at a minimum (yes blanketed horses can shiver), so muscle tone wasn’t involved, i.e. there wasn’t a tired horse. Turning the horses out, properly attired, was helpful, as was free lounging in the schools, quiet workouts without sweating the horse, quarter sheets and coolers and heaters in the barn aisle all good.
For the heat, I don’t work anything over 100 degrees. The horses all get electrolytes in their water and free access to salt licks. I have also added water to pellets at competitions – or maybe a double handful of pellets to the water bucket to encourage drinking or water ingestion. I frequently add gatorade or like product – the VSE just drinks it out of the bottle. I make sure the horses have shade when not working and fly spray. This year I got a water sprinkler that goes on a t-post and rotates 360 degrees. At the hottest part of the day, I turn it on and it sprays the mustang’s corral and the VSEs’ corral in a big circle. I might leave it on 30 minutes, shut it off and repeat in an hour. That way they get the spray, the ground stays wet and cooler, their hooves have an opportunity for moisture (people often forget that the hooves dry out, become more brittle, break and chip, shoes won’t stayed nailed, etc. Giving them moisture each day – natural, not paint-ons, makes a good difference.)
Finally, keeping an eye on the horse’s indications is all. The mustang couldn’t care less what the temps and weather are – she would go until she dropped dead, so a very structured workout is necessary. Sometimes we will just hitch and go for a particular distance at a particular pace and then be absolutely done and home for a hose-off. Sometimes we will work on a particular hazard, in a particular pattern, or a set of dressage movements, but very structured in time and energy expenditure, so she doesn’t over extend. I have a synthetic harness, so I can hose off horse and harness all at once – which benefits us all!
On the other side of the scale is the VSE: hates the heat. His dressage becomes something more like a death march. So when very hot, we just go out for slow distances – especially if it looks like rain, which he loves!
So best things that have worked for me:
No work below freezing – and keep in mind wind chill
No work over 100 – electrolytes, wet feeds and lots of hosing
Be ready to work early morning – I start at 5AM in the summer, but give them until noon in the winter
Know the horse and its indicators