Fluid losses occur by a variety of routes. In horses on full feed, the principal loss of water is in the manure (normally formed fecal balls are approximately 75 percent water). The next most obvious source of fluid loss is in the urine. The quantity of urine formed depends in large measure on the amount of water consumed and on the nitrogen and electrolyte composition of the diet. Salt-supplemented horses on an all-alfalfa ration may have urinary water losses of 12 to 16 liters daily, i.e., 3 to 4 gallons of urine per day. If horses are not provided access to salt, or if they are off feed, urine output may be as little as 2 or 3 liters per day, i.e. less than a gallon. The third obvious route of fluid loss in horses is sweating. Like people, horses sweat profusely. Sweating is an essential means of regulating body temperature in the exercising horse. Substantial fluid and electrolyte losses occur with heavy sweating. Horses may lose 10 to 15 liters (2.5 to 4 gallons) of water per hour through heavy sweating.

We all know that sweat is salty, and when horses (or people) sweat they lose a large amount of salt as well as water. The chief electrolytes lost in sweat are sodium and chloride, along with some potassium. Heavy sweating can result in serious dehydration if fluid losses are not promptly replaced by voluntary consumption.

The final route of fluid loss is as “insensible” losses from the respiratory tract and skin. Fluid lost from these sources does not contain any electrolytes but is simply lost as water.

The water management in horses often brings out various controversial issues. In most stables in the old days the horses did not have a free access to water, as it is propagated and practiced in this age. 30 some years ago in Europe I was working in a racing stable with about 50 racehorses. The water was given three times per day (no water buckets in the stalls), in the morning (about one hour before work), at noon before the first daily feeding of grain (horses were not fed at all in the morning) and finally in the evening before the second feeding of hay and grain. Horses were bedded on the straw and receive all the hay they could eat. No water was given to horses during the so-called cooling out process, which was actually done under the saddle (horses were not hand walked, only after a race). The horses were fed meadow hay, which is for most part rich in minerals as well as electrolytes. Horses were not receiving any additional salt or electrolytes supplements, nor there were any salt blocks available. The only time the salt was fed was during the once per week feeding of mash, usually after a race or hard work out. I recall no colic, not even one case, no tying up, nor there were any problems associated with dehydration. The horses were fed the meadow hay after they were cooled out and then received water before grain feedings as previously mentioned. I believe that this type of water management enabled the horses system to balance his electrolytes better, thus retaining a constant hydration. Also in my younger days, the agriculture horse spend most of his day working, while again receiving the water only three times per day with no obvious problems with his health, despite the 8 hours working day in hot days during the summer months.

Today’s concept of free access to water is somewhat unnatural and I believe that it often results in insufficient water intake on the part of the animal (especially during winter), since the system does not adopt to “drink – to store” the water in the body. As I have noticed that the dehydration in horses that participate in various strenuous competitions like racing is often a problem, despite of various additions of electrolytes. I believe that such water management disables the horse’s body to naturally retain and regulate water, while on the other hand often causes more extreme sweating. I am not suggesting that one should abandon the “free access” to water in the stable, especially not if the horse is accustomed to it. Therefore, one needs to take into consideration the kind of water access the horse is accustomed to before making any adjustment or changes in the water supply. I also believe that cooling down the horse with water while walking, as it is customary these days, is also to some degree detrimental.

The sunk-in flank is obvious in this case of dehydration and malnutrition.

“tenting” the skin. In the normal well-hydrated horse, the pinched skin will snap back to normal very quickly, within a second or two.

If and when one wishes to give the horse some water immediately after hard exercise during extremely hot weather, one or two gallons (4 – 8 liters) at most given slowly over period of 15 minutes can be of some help, however, walking the horse till he finishes drinking is somewhat foolish. Most of the water will go right through the horse and when put back into the stall, such horse usually keeps perspiring, thus again losing more of the precious electrolytes and water during extreme hot summer days after hard work, or stands a good chance to catch the chills during cold days in the winter months. It is no wonder that so many performance horses these days tend to have dehydration related problems with electrolytes imbalance.

When the horse has a free access to water it does not mean that the body has enough of it. Daily observation of the moisture in the manure is important in order to establish what is normal for the particular horse. The dryer than normal feces signal early signs of dehydration and also possible danger of colic. The too loose feces can lead to excessive loss of fluids and cause dehydration.

One of the simplest and most useful procedures to evaluate the degree of dehydration is to observe the response of the horse’s skin to a pinch on the neck, just in front of the shoulders, or on the upper eyelid-a procedure known as “tenting” the skin. In the normal well-hydrated horse, the pinched skin will snap back to normal very quickly, within a second or two. With slight dehydration (about 5 percent of body weight) the skin will remain raised or “tented” for 2 or 3 seconds following the pinch. With progressively more severe dehydration, up to 10 percent of body weight or more, the skin may remain tented for 5 to 10 seconds. The severely dehydrated horse will have a dry mouth and the eyes may be sunken deeper in their sockets. If these signs are evident, severe dehydration is present and veterinary assistance should be sought immediately.

There are significant differences among horses in their response to a skin pinch. Newborn foals and very thin horses have little fat under the skin. Their skin will tent up fairly markedly, certainly much more so than that of an overweight horse with a great deal of fat under the skin. It is important for an owner to assess how a horse responds to tenting of the skin under normal circumstances, so that a dehydration abnormality, if and when it occurs, can be easily recognized.

There is also another exterior sign that can help us evaluate the hydrated condition of the horse. Horses lacking water are unusually sucked-in at the flanks, which is usually the obvious and first sign of lack of water in the body. The sucked in flanks can be usually noticed immediately after excessive sweating either due to hard work or prolonged trip in the van etc. Therefore the feeding of mash is essential immediately after such trip or work, providing the horse will not be worked hard the next day, in which case he shouldn’t if in such shape. The sucked-in flanks are always very obvious and present in horses suffering from dehydration.

The proper monitoring of the horse’s condition as well as his food consumption and water intake can prevent serious effects caused by inadequate amount of water in the horses system, mainly dehydration, lost of appetite, weight loss, colic, loss of energy etc. Too much water in the horse’s system can be also detrimental, mainly during performance, especially in winter months.

The regular feeding of mash is an important part in feeding of horses, water management, and in the prevention of dehydration and colic.


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