Water Balance in Giraffes

Wild giraffes live in arid environments. Having access to water and minimizing water requirements are critical. The main sources of water are the water in browse and water generated by metabolism. Giraffes rely less on surface water: intermittent use of surface water is a legendary characteristic of giraffes. The volume of water needed depends on body mass. For a giraffe weighing 750 kg, ~25 L of water is needed daily. The water content of browse is ~60%, and as a giraffe of that mass will eat ~35 kg of fresh browse daily, it simultaneously will acquire ~20 L of water. Metabolism of the fat, carbohydrates, and proteins in 35 kg of fresh browse will produce ~10 L of water. These two sources of water exceed daily requirements and reduce the need to drink surface water. Water is lost through feces, evaporation from the skin and respiratory tract, and in urine. Fecal water loss and water lost in exhaled air amount to ~4 L daily (~2 L each). It is not known if giraffes sweat, but their skin contains active sweat glands. The volume of water lost as sweat will vary according to what thermoregulatory mechanisms are activated to minimize sweating, but may be 5 L daily. Obligatory excretion of water-soluble wastes in urine can account for most water lost daily, and that amount is related to kidney anatomy and function. In a 750-kg giraffe, obligatory urine volume is ~10 L daily.