Under conditions of restricted water intake, an animal may concentrate its urine by reabsorbing a greater amount of water than usual. While this capacity for concentration of the urine is limited, it can reduce water requirement some. When an animal consumes a diet high in protein or in salt or containing substances having a diuretic effect, the excretion of urine is increased and so is the water requirement. The water lost in the feces depends largely on the diet and the species. For instance, substances in the diet which have a diarrheic effect will increase water loss by this route.
Cattle excrete feces of a high moisture content, while sheep excrete relatively dry feces.
The amount of water lost through evaporation from the skin or lungs is important and in some cases may even exceed that lost in the urine. From a practical point of view, all of these factors and their interplay make the minimum water requirement difficult to assess. Since feeds themselves contain some water and the oxidation of certain nutrients in feeds produces water, not all must be provided as drinking water. Feeds such as silages, green chop or pasture are usually high in moisture, while grains and hays are low. High energy feeds produce much metabolic water, while low energy feeds produce little.