Water Intoxication

The rapid ingestion of large amounts of water by young calves with normal serum sodium concentrations may result in intravascular hemolysis, hemoglobinemia, and hemoglobinuria.


Aetiology

The ingestion of excessive quantities of water when animals are very thirsty may result in overhydration, which is also called water intoxication. The primary cause of acute overhydration is a rapid decrease in the osmolality of the small intestinal contents, which are normally isotonic to plasma. Such a rapid decrease in luminal osmolality occurs within five (5) minutes of water ingestion because thirsty calves close their esophageal groove when drinking. This results in a large volume of water in the abomasum, which is subsequently emptied into the duodenum. Free water rapidly moves from the small intestinal lumen into the intravascular compartment. The end result is a rapid decrease in plasma osmolality and expansion and rupture of red blood cells, leading to intravascular hemolysis, hemoglobinemia, hemoglobinuria, hyponatremia, hypochloremia and a decrease in plasma protein concentration.


Epidemiology

Calves 2 to 4 months of age are most commonly affected, but the disease is also recorded in adult cattle, sheep, and goats. Water intoxication occurs in calves in normal husbandry systems when animals that have had limited access to water are suddenly given free access. The majority of calves show clinical signs within minutes to hours of access to water.


Clinical Findings

Hemoglobinuria as a result of intravascular hemolysis is prominent, and there may be a moderate to severe hemolytic anemia. Dark red urine is passed shortly following access to water. Additional signs include tachycardia and hypothermia if the temperature of the water ingested is below body temperature. Affected animals are usually depressed and weak.


Treatment

Treatment of affected animals is usually not attempted because hypoosmotic lysis has already occurred when clinical signs have manifested, and serum osmolality is usually gradually increasing as the kidneys eliminate excessive free water. Hypertonic saline (7.2% NaCl, 5 mL/kg BW over 5 minutes intravenously) is usually administered to correct the hyponatremia and hypochloremia, but treatment is not necessary in mild cases.

Case fatality is low, and hemoglobinuria persists for only a few hours.


Control

Water intoxication is not common and can be avoided by preventing thirsty animals from having unlimited access to water. Calves should have free access to water as soon as they are born.