James Bryant DVM, Diplomate ACVS
In the sport of endurance there is some controversy surrounding the pre-ride use of intravenous fluids. I think it is very important to define the purpose of the fluids because there are both appropriate and inappropriate uses of fluids. First, the use of intravenous fluids as a pre-race supplement has remained and should remain controversial for years. The use of so-called jugs (IV fluids and vitamins and electrolytes) once a staple on the race track and through the recent years while still performed by some the physiologic benefits have been proven to be less and less important. In addition the kidneys are designed to remove excessive fluid from the body, therefore if you give fluids to a well hydrated horse they are likely to urinate the extra and therefore not expand the pre-race blood volume. Therefore unless you are starting a ride with a dehydrated horse (which none of us would ever advocate) the benefit of fluids in the 24 hours prior to a ride is likely non-existent.
Second, the use of intravenous fluids following travel seems to have some controversy around it which I find as completely inappropriate. When people travel long distances in planes it is recommended that you drink plenty of fluids (water) and when you arrive at your destination continue do so for the first 24 hours. We all know that after long travels we feel tired, dehydrated, run down and take 1 to 3 days to feel like ourselves again. To assume that horses are somehow different and have no ill effects systemically with travel makes no sense. When blood work is performed on horses that have traveled wether 10 hours or more by trailer and/or over 6 hours by plane we find that over 80% of the horses have an elevation in there PCV (packed cell volume) and TP (Total protein) these values are indicators of the amount of fluid (water) in the blood stream. These elevations are consistently above the well above the normal for the individual horse and some times very elevated consistent with sever dehydration. Therefore the overall effect of the travel results in some form of dehydration even with access to water throughout the trip.
In particular to endurance horses that travel long distances by ground or plane we have great concern over starting an event (or even training) a horse that is dehydrated. We know for a fact that on a 100 mile ride an endurance horse can be expected to lose at least 3 to 5% of its body weight in water during the event by the finish. Horse that are in metabolic trouble can lose over 10% and can be in severe danger of colic, exhaustion, dehydration, laminitis and even death. From past experiences we have learned t (sometimes the hard way) that horses can tie-up after long travel. Part of what occurs here is the dehydration from travel has contributed to a lower blood volume and therefore the muscles are not perfused as well and basically starve of oxygen in the first or second workout and then these cells die and release the muscles enzymes and you have a tied up horse. In addition if they tie-up and are dehydrated now you have created an environment that the kidneys can fail from the lack of fluid and large accumulation of the myoglobin from the muscle breakdown. In this scenario not only will the horse not be able to compete but may die from the renal failure. More commonly however the question is can the horse recover in time to compete or do they compete but compete poorly due to the subsequent issues. When you travel with your horse long distance to an important race you want to have them in peak form with no lingering issues from travel.
Lastly, how is it best to rehydrate a horse after travel. Consider three possibilities, 1) Let them drink and feed food that is as wet as possible with as much water as they will eat. In this scenario I would also recommend blood work to ascertain if the PCV and TP are back to normal and would not exercise the horse until they are normalized. 2) Use oral fluids given through an nasogastric tube. This is an appropriate way to administer fluids, however water absorption from the GI tract may be slowed in the first 24 hours due to ileus (slowing of gut motility) from travel and may require 1 to 2 days of administration. 3) Intravenous fluids are a direct way to restore vascular volume. Typically volumes of 10 to 20 liters of physiologic fluid (saline) are recommended for horses that are 3 to 5% dehydrated. The body is a very powerful tool and will eliminate the excessive fluid when appropriate and distribute what is needed to the body. Blood work is extremely helpful to assess the effects of the IV fluids and to decide how much is needed. In addition the color and volume of urine can assist in gauging the needed volumes.
In the horses traveling to Malaysia for the World Endurance Championships it was deemed of the utmost importance of the veterinary staff and Chef d’quipe that the horses be as metabolically stable as possible from the travel and as ready for training and acclimation to the hot and humid environment. We have been rewarded by our forward thinking with blood work upon arrival in Malaysia that indicated that 3 of the 6 horses were moderately dehydrated (33% elevation from there normal PCV) and 3 of the 6 were mildly dehydrated (10 to 12 %). The day after the second leg of there flight the horses clinically appear well hydrated and blood work revealed a return to normal ranges. The horses continue to walk at this point but they are physiologically prepared to train now rather than 1 week from now with limited time for preparation.
To assume that horses that travel over 24 hours in a plane plus 6 hours of time in the pallet prior to loading and unloading are prepared to bounce back and perform at their best quickly does not consider what the effect of the same travel would be to us. In addition we are not here to just compete we are here to show how good our horses and riders are to the rest of the world. Not taking advantage of all the things we as professional veterinarian (or better yet sports medicine clinicians) have to offer in preparing for such an event at the peak performance of the athlete is like saying we are traveling to lose. Remember we are asking these wonderful equine athletes to perform at the very edge of maximum exercise, if we can why should we not help them be at their best physiologically. We owe that much to them.