Most of us are aware that working horses lose water in sweat during work but don't always consider the considerable amounts of moisture lost from the respiratory tract, in manure and in normal urination. Unless you weigh your horse before and after work, it can be easy to underestimate the amount of total fluid loss in cool, dry conditions when sweat may evaporate quickly. It's important that you become familiar with signs that may indicate dehydration - elevated heart rate or poor heart rate recovery, elevated respiratory (breathing) rate, dry mucous membranes, slow capillary refill time or prolonged skin tenting - and to know what's normal for your horse.

Mares with suckling foals are providing fluid for two and their water requirements are two to three times normal maintenance needs. These requirements are also increased by warm, dry or windy conditions. Mare's milk is usually the foal's only source of water (fluid) during the first critical weeks - if the mare becomes dehydrated, so will the foal.

If you use automatic waterers or floats, it's impossible to measure water intake unless they are fitted with a meter. A horse may easily become dehydrated if the auto waterer should freeze or malfunction. 

 

If you notice your horses' water intake dropping off in the winter, it may be necessary to warm their water either by adding a heater (with a GFI electrical circuit for their protection) or by adding warm or hot water to their tanks or buckets. Make sure your horses are not avoiding a heated water source - approaching but not drinking may be an indication of a ground fault that is shocking your horse.

Sodium and Chloride (NaCl or "salt") play critical roles in the body's metabolism and are tightly regulated in the blood. Because blood levels are so tightly regulated, standard tests may not indicate a sodium deficiency at the cellular level. When ingested salt levels are low, the body will respond by pulling salt from interstitial fluid into the bloodstream, and by increasing the reabsorption of sodium by the kidneys. (For details on some of the mechanisms involved in sodium regulation, see http://lpi.oregonstate.edu/infocenter/minerals/sodium/

Feeding salt on a regular basis at or above the NRC recommended levels helps ensure an adequate thirst response. After the cells and interstitial fluid have reached an equilibrium, excess sodium is normally excreted by the kidneys.

The minimum requirement for sodium in a 1,000 lb horse ranges from 9-10 grams at maintenance, 16 grams in moderate work, to 37 grams in very heavy work. This is roughly equivalent to a range of from 1 to 3+ ounces of salt per day. Forages may supply as little as 1 to 2 grams of sodium per day. The best way to making up the sodium deficit is by adding salt directly to the feed. If using a salt block - which should always be plain white salt - not mineralized - the amount of sodium it provides should be calculated and the horse's consumption monitored to ensure adequate intake. Keeping loose plain white salt available is preferable to using blocks.

Sodium (and chloride) requirements remain steady except when accounting for sweat loss during sustained work - which can cause large increases. Many commercial electrolyte formulas contain high levels of potassium but insufficient sodium and chloride - you should have an understanding of what your horse actually needs before simply adding electrolytes. Electrolytes should never be given to an already dehydrated horse which is not drinking well unless alternative fluids are also given by tube or IV.

If you suspect your horses aren't drinking as well as they could, try adding water to their concentrate  feed.  Many horses also enjoy an extra beet pulp "slurpee" - long a mainstay of endurance riders. You can add additional salt to this so they're not getting their extra salt all at one feeding. If your watching weight - simply reduce the dry hay fed to compensate for the added beet pulp. Wetting down their hay with a hose or dunking hay nets can also add considerable moisture.

As weather changes and horses are transitioned from summer to winter feeding routines, some horses may simply need a jump start to encourage adequate drinking, while others may need closer watching. A well hydrated horse will more easily handle the extremes of winter weather and activity. Taking the time to monitor his water intake can set your mind at ease, knowing that you've minimized his risk for cold-weather related colic and respiratory problems.