Water intoxication—too much of a good thing
As Texas experiences one if its worst droughts on record, the Texas Veterinary Medical Diagnostic Lab (TVMDL) in Amarillo, TX, is reporting increased numbers of cattle dying from water intoxication. Although rare, water intoxication occurs when cattle over-drink, usually following a period of water deprivation. It can produce acute death in a majority of cases.
"This year we are getting feedback from the field of an increase in the number of water intoxication deaths in cattle versus the one or two cases that normally occur per year," said Dr. Robert Sprowls, veterinarian at TVMDL. "Climatic conditions in 2011 with intense heat, low humidity and minimal moisture content in forage have contributed to this situation."
Natural sources of water are diminishing across the state, forcing producers to haul water or move their livestock this summer. In addition to extreme drought conditions, Texas has been dealing with steady high heat. These two factors combine causing decreased moisture content in plants.
"Cattle normally receive a portion of their daily water requirements from grazed forage which rehydrates them while grazing pastures or range. An average cow grazing green forage consumes about 3.5-8.4 gallons of water daily," explained Dr. Ted McCollum of the Texas AgriLife Extension Service." This year, as a result of no forage growth and a relatively low intake of dry forage, daily water consumption from grazed forage only provides 0.4–0.6 gallons daily."
Water intoxication typically follows water deprivation which occurs when cattle cannot, or sometimes will not, consume enough water. Many factors can predispose to water deprivation in cattle that are already experiencing decreases in water consumption from dry forage. This summer has seen many surface tanks and streams dry up. Water deprivation has been seen perhaps more commonly in these situations. Deprivation can accidentally occur when there are malfunctions in water systems. Deprivation can also occur even when it looks like there is plenty of water.
Cattle behavior can also play a part in their susceptibility to water deprivation. They are creatures of habit and may become anxious to return to their previous grazing sites even if the tanks are dried up and boggy or the availability of water is gone. It should never be assumed that cattle will locate on water by themselves after moving to a new location and it’s important that they be driven to and held up on water in new pastures. They still may walk the fence to return to their previous watering site.
"Water deprived cattle over-drink because they are thirsty," said TVMDL’s Sprowls. "But when cattle over-consume water and rehydrate too quickly, a disruption in electrolyte balance leads to more water moving into the brain, resulting in edema."
There is a physiologic balance between water within cells and water outside the cells that are within in the body tissues. When over-consumption of water occurs in a dehydrated animal, there is a rapid progression of the normal transfer of fluid into the cells in the brain which then lead to brain swelling.
"Consequently, clinical signs include wobbliness, stumbling, seizures and acute death. Cattle can die within two to three hours and are often found dead next to a water source," described Sprowls. "Owners report finding several dead cattle next to stock tanks where they have just been moved to. It progresses pretty quickly. The cattle that remain standing usually survive without complication. But if they ‘hit the ground,’ they typically die fairly quickly."
Water intoxication does not look or behave like classic polioencephalomalacia secondary to thiamine deficiency. Water intoxication is usually a clinical diagnosis based on the history of water deprivation followed by access to and over-drinking from a new water source as described by the veterinarian or cattle owner. On postmortem examination of these animals, the excessive water has usually already moved out of the rumen. The disease can be confirmed with tissue samples taken from the brain.
"Cattle can usually survive a day or two without water, sometimes three or four days in a wet spring when there’s lots of moisture in the grass and the ambient temperatures are mild," Sprowls explained. "But with dry forage, high heat, low humidity and evaporation of water from panting, cattle can get into trouble quick. When some water-deprived cattle over-consume, the time interval between over-hydrating and clinical signs can be short."
McCollum added that with surface water down in tanks and ponds and virtually no rain this year, evaporation from the triple-digit heat has been concentrating salts and mineral solids which affect water quality.
Water deprivation/water intoxication is a management problem which has been intensified with this summer’s unrelenting heat coupled with Texas’ ongoing drought. It’s difficult physiologically for water-deprived cattle to go from no water to free choice water in conditions being presented this summer. And it’s difficult to regulate water consumption in a thirsty cow.
This problem stresses the importance of locating cattle on water when moved to new pastures from situations where they’ve been water deprived for various reasons. Slow, limited access to initial minimal amounts of water in troughs is a potential way to prevent immediate over-consumption of water in cattle that have been water deprived. But that may be easier said than done with a thirsty cow. — Ginger Elliott, WLJ Correspondent