– Steve Boyles, OSU Extension Beef Specialist
The water needs of livestock are filled from three major sources:
(1) Free drinking water
(2) Water contained in feed
(3) Metabolic water produced by oxidation of organic nutrients
Water contained in or on the feed is extremely variable. It may range from a low of 5% in dry grains to about 90% in young, fast-growing grasses. In addition, the amount of dew or precipitation on the grass at the time of grazing is available as well.
Water losses by animals are principally through:
(3) Evaporation from the body surface and respiratory tract.
In ruminants the loss of water through feces is equal to urinary losses. The high-fiber nature of ruminant diets requires more water to carry the ingesta through the gastrointestinal tract than for non-ruminants. Cattle feces contain 75-85% water, while sheep and goat feces have 60-65% water.
Expired air is over 90% saturated. When respiration rate increases in response to high temperatures or other behavioral stimulus, the rate of respiratory water loss is increased
There are large differences among species in the importance of sweating with domestic livestock ranked in the descending order of horses, donkeys, cattle, goats, sheep, and swine. The threshold skin temperature for sweating varies among species with cattle reacting at about 77° F
Factors Affecting Water Intake: Young calves generally have higher intakes of water per unit of weight than older cattle. During the last 4 months of pregnancy, cows may consume 30% more water than when dry and open. The estimated intake of free water for lactating cows is about 2 pounds of water per pound of milk produced. This could be an important factor in early calving herds where frozen water is an issue.
Frequency of Watering: When cattle on grazing have water available free choice, they drink 2 to 5 times per day. Water intake of sheep or cattle will decline as distance to water sources increases.
Physical form of the diet influences water consumption. When the same forage crop was made into both hay and silage, Holstein heifers on the silage diet had higher total water intake (free + feed) and secreted more urine than heifers on hay alone.
Water Temperature: Findings on the effect of temperature on water intake are variable. Water temperature (assuming not frozen) does not appear to alter rate of digestion but there have been some reports on variation of animal performance.
Air Temperature: Under controlled temperature conditions it has been demonstrated that cattle tend to increase water intake as temperature rises with 81°F being the temperature where marked changes in intake by lactating cows is noted. Below that point water consumption is considered largely a function of dry matter intake.
Source: Effect of Environment on Nutrient Requirement of Domestic Animals. National Academy Press. https://www.nap.edu/read/4963/chapter/1
Related reading: Livestock and Water http://agnr.osu.edu/sites/agnr/files/imce/pdfs/Beef/LivestockAndWater.pdf