Horses need access to cool, clean water in the hot summer months.

In these hot summer months, it is important to consider your horse’s water consumption needs. High temperatures necessitate access to cool, clean water.

Horses will consume as much as 60% more water when it is cooler than the outside temperature during the hot months. A horse only needs one quart of water per pound of feed at 0F (18C), but a gallon of water in required at 100F (38C). Activity may increase a horse’s water requirement by as much as 300%. When a horse is hot and tired, it’s recommended to wait for at least 30 minutes before giving it unlimited access to water to prevent colic. Colic can progress to laminitis and eventually founder.

A dehydrated horse will have sunken eyes, its flank will be tucked up, and it will have less skin elasticity. Level of dehydration can be checked for by grasping the skin, releasing and watching it return to normal. A two to five second return indicates mild dehydration – a five to ten second return indicates severe dehydration. Veterinary administered fluid and electrolyte therapy may be required in some cases.

A horse can live longer without food than water. Two days without water will produce colic. Experiments conducted in France in 1882 proved that horses can live only five or six days without water, but can live 20 to 25 days without food if they have water. In winter, horses have gone several months without water if they can eat snow. It takes about 12 quarts of snow to make one quart of water.

Water is important in digestion, in body temperature regulation, and in waste removal. An 1100 pound horse is composed of nearly 90 gallons of water or 70% of its body weight. Dehydration can be due to lack of water supply, water with high mineral or salt content causing severe diarrhea, illness causing diarrhea, sweating due to work or nervousness, or inability to drink due to physical impairment.

Compared to other species, the horse has a high capacity for athletic activity, yet a reduced ability to dissipate heat due to a large muscle mass and a relatively small body surface area. During exercise the metabolic rate and rate of heat generation may increase as much as 50 times with 80% of generated energy given off as heat. The body’s ability to dissipate heat is reduced by: high temperature, high humidity, diminished ability to sweat, exposure to direct sunlight, and lack of air movement.

A lactating mare producing 30 pounds of milk per day requires an additional five gallons of water over the normal maintenance requirement. Lactation may increase the water requirement by 50 to 100%. Be sure to have enough buckets or water containers in the stall or pen to provide for individual needs. Over consumption of water is rare but more likely to occur when automatic waterers are used in stalls.

Traveling horses may reduce water consumption due to taste preferences. This can be solved by hauling water from your home water source, flavoring the horse’s water at home with pop or Kool-Aid and then making the same solution away from home, feeding a wet feed such as bran mash, or teaching your horse to drink from a hose. Water intake is said to be influenced by its pH. Water testing is necessary in suspect areas. Arab horses in general are more resilient to water deprivation than other horse breeds.

Water or feed toxicity can be a problem, especially in summer months. In the mid-west, Selenium toxicity or alkali disease can be a problem when horses consume water with high Selenium content. Selenium is an unusual mineral since a small amount is required for normal body function, but an excess outside the normal narrow range produces disease. A horse that has been “alkalied” will often slough its mane and tail hair and appear to be foundered. Recovery is possible by replacing the offending water and feed source. The hooves often slough and have to be cared by shoeing with therapeutic shoes during the recovery period. On the east and west coast Selenium deficiency is a problem that is remedied by adding a small amount of the mineral to the feed.

Drought conditions can cause pastured horses to eat green toxic plants that they normally would avoid. Accumulator plants that take up toxic elements from the soil such as Selenium may become more attractive to them during these stressful conditions when other plants won’t grow.

Toxic blue-green algae can be a significant problem in summer water sources. The active toxins are produced by more than 30 species of cyanobacteria. Long lasting warm weather leads to more extensive concentration of the toxic bacteria. Up to 90% of a lethal dose can be ingested without an outwardly visible effect. Death results from liver hemorrage and hypervolemic shock. Neurotoxins cause death proceeded by muscle tremors. Animals that survive acute poisoning can have signs of photo sensitization in areas exposed to light such as the nose, ears and back followed by hair loss and sloughing of skin.

Prevention involves regularly cleaning water troughs or removing animals from access to affected water. Copper sulfate (CuSO4) can be added to pond water to prevent algae growth. The National Research Council (NRC) recommends 0.65 – 1.3 oz/ 10,000 gallons or 1.4 – 2.8 pds / acre feet of water. The addition of gold fish or cat fish to eat algae at the rate of one fish for every 100 gallons in a tank has been recommended as an alternative. Treatment of water with chlorine or ozone is not recommended by Merck since it will result in the release of free cyanotoxin. One case of toxicity reported in a vet journal was of a pony that drank swimming pool water treated with the algicide Vinylchlor.

Be safe and be sure your horse has sufficient clean, cool, fresh water during the hot summer months. The NRC recommends a water to feed ratio of 3.6 to 1 for horses or about 4 pounds of water for every pound of food. Therefore, a horse eating 20 pounds of dry feed (2% of its body weight of a 1000 pound horse) should drink about two five gallon buckets of water per day since a gallon weighs about 8 pounds. Horses grazing damp pasture grass may drink less since grass can contain 60 to 75% water whereas hay is only 10% water. Horses on a protein rich diet such as alfalfa hay will drink more than horses on grass hay. Sweating working horses will drink more than idle ones.

However, horses have individual preferences and the old adage applies, “You can lead a horse to water but you can’t make him drink.”