After a ride you may notice your horse sweating, because that is the number one method horses use to keep cool. The longer the ride and the hotter the weather, the more sweat is lost. Sweat is made up of water and electrolytes, and some German researchers described various patterns and estimated sweat loss with each one. Sweat loss is reported in liters, and a liter is about the same as a quart.
The researchers report that if the area under the saddle and throat are wet and there are small white areas at the corners of the saddle, four to seven liters of sweat has been lost. If there is foam on the bridle and noseband, the flanks are wet, and the area under the saddle and girth are wet, then the horse has lost seven to nine liters. If the throat and flanks are wet, the area above the eyes is moist and has dark wrinkles and foaming between the limbs, nine to 12 liters has been lost. If the horse is actually dripping fluid above the eyes and under the belly, it is estimated 12-18 liters water has been lost, which is three to four gallons of water loss. So you can see water loss, particularly in hot weather is a major concern, and electrolytes are lost at the same time.
Dehydration is a major issue and you need to know how to determine if your horse is dehydrated. With dehydration, the skin becomes less elastic, so the best way to start is with a skin elasticity test. If the horse is mildly dehydrated, when you grasp the skin on the horse's shoulder and pull it up in a tent shape, the skin will remain tented for two seconds. With severe dehydration, the skin will tent for four to five seconds.
Another method to check for dehydration is to check capillary refill time. Simply lift your horse's lip and the gum tissue should be pink and moist. If it is tacky and your finger temporarily sticks to the gum, the horse is dehydrated. Press on the gum with your finger and the pink color should return in at least two seconds, as longer indicates dehydration or decreased circulation. If your horse is dehydrated, not only is water needed but electrolytes are too; the most important electrolytes are sodium, chloride, and potassium. If your horse is already dehydrated, your vet can give your horse oral fluids with a nasogastric tube and can add electrolytes to the mixture. If the dehydration is more severe, intravenous fluids with electrolytes may also be required.
It is better to prevent dehydration and electrolyte deficits than to treat it. This involves making sure your horse is given electrolytes in the feed, especially before exercise in hot weather. Make sure the electrolyte you choose contains a large amount of sodium chloride.
In hot weather, I recommend to many of my clients that they add an ounce of table salt and an ounce of lite salt to their horse's feed twice a day.