Thursday, October 23, 2008

Winter Water Needs for Our Horses

As cold weather approaches (and already here for those in the North), we need to continue to pay attention to our horses' water intake. Horses who are used to obtaining some of their fluid from grasses may not increase their water intake as pastures brown up or as their winter ration begins to include more cured hay. 

Risks of Lowered Water Intake
Impaction colic, related to a diet of drier forage coupled with lessened water consumption is not the only risk to horses who drink less in cooler weather. Dehydration may also expose horses to increased respiratory problems. While I could find no direct equine references, in humans, dehydration is associated with poor mucus mobilization and clearance, with a lessening of a critical airway defense mechanism. (

The maintenance water intake for an adult non-working horse is around 5 L per 100 kg/BW (NRC 2007, p132). This translates to about 1.3 gallons for each 220 lbs your horse weighs. You can figure your horse's minimum requirement by dividing his weight by 220, then multiplying by 1.3, or you can find the closest weight in the chart below.

Horse’s Weight

Minimum Daily Water Requirement

220 lbs

1.3 gallons

440 lbs

2.6 gallons

660 lbs

3.9 gallons

880 lbs

5.2 gallons

1000 lbs

5.9 gallons

1100 lbs

6.5 gallons

1320 lbs

7.8 gallons

1540 lbs

9.1 gallons

These requirements are increased by dry, windy or warm weather conditions, work or lactation. 

Work Related Fluid Losses
Most of us are aware that working horses lose water in sweat during work but don't always consider that substantial moisture is also lost from the respiratory tract. Unless you weigh your horse before and after work, it may 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, skin tenting - and to know what's normal for your horse.

Lactating Mares
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.

Monitoring Water Intake
If you use automatic waterers or floats, it's impossible to measure water intake unless they are fitted with a meter. A horse may also become dehydrated if the auto waterer should freeze or malfunction.
If you notice your horses' water intake dropping off, 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.

The Role of Salt
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

Feeding salt on a regular basis at the NRC recommended levels helps ensure an adequate thirst response. After the interstitial fluid has reached an equilibrium, excess sodium, in the absence of disease, will be excreted by the kidneys.

The minimum requirement for sodium in a 1,000 lb horse ranges from 9 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, the amount of sodium it provides should be calculated and the horse's consumption monitored to ensure adequate intake.

 These requirements remain steady except when accounting for sweat loss during 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 you actually need before simply adding electrolytes (and never give electrolytes to an already dehydrated horse).

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.

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