We at Perseverance are not in favour of intravenous fluid drips before or after major events, but that is just our opinion. Many professionals argue that highly competitive horses are assisted by such intervention, and it is fairly common at international events.
Sometimes tired and dehydrated endurance horses are deemed in need of help in rehydrating after endurance events. Sometimes large volumes of isotonic saline are given. Occasionally the horse rehydrates but does not improve. Instead it goes into distress.This can happen if the horse had very low sodium. The added isotonic sodium adds fluids and electrolytes but not enough extra sodium to correct the imbalance. In such cases the horse can develop brain edema which is life threatening.
What the horse needs is more salt – sodium. Hypertonic saline is what the horse needs.
This article by respected endurance vet, Nancy Loving, explains its various uses:
In fact, it is often the inappropriate use of oral electrolytes that creates a dangerous metabolic situation, particularly when it comes to potassium. If the horse is not drinking sufficient water and the rider persists in giving the usual sort of electrolyte , the high potassium can suppress the thirst reflex altogether thus creating a state of dehydration. High sodium makes a horse thirsty, not high potassium.
If sodium is low, the body knows not to dilute the sodium more by drinking water. In the old days, horses were not allowed to drink at all during work; not until they had cooled off at the end of the day. We know that we must let our horses drink during the ride but we make sure they have enough salt before and during the ride so that they do not get low sodium. Some people think the oral electrolyte mix for endurance horses contains enough salt and do not feed extra in the diet. This can lead to problems.
Also, a horse can finish a hard race tired, and every horse that has been on the track for 5 or 6 hours has a degree of dehydration, this is all normal and in no way life threatening. However, putting a needle in the vein and dripping a lot of fluid in will rehydrate the horse quickly, but I believe it can turn a tired horse into a very sick horse if all factors are not under control.
Giving salt by mouth and allowing the horse time to drink and rehydrate in its own time is the proper way to do it, I believe.