Salt poisoning can occur in pigs either as a consequence of water deprivation or from sudden ingestion of too much salt.
Poisoning in water-deprived pigs can occur in pigs consuming a proper level of salt but it is more likely if the salt level in the feed is excessive. Signs often are precipitated, or worsened, by allowing the pigs sudden, unlimited access to water. Water deprivation can occur for many reasons but commonly may be the result of freezing of the water source, plugged water nipples, or inadvertently leaving a water valve closed. Operators may not always be forthright in admitting human errors related to water deprivation. Poisoning has occurred following prolonged shipping without access to water, followed by unlimited access.
Following sudden heavy rains, salt poisoning can occur in swine after ingestion of salty brine from overflowing, loose-salt boxes provided for other livestock and is also reported following ingestion of whey. This type of poisoning is more likely in water-deprived pigs.
Clinical signs of sodium ion toxicosis are caused by the acute cerebral edema that occurs as a result of multiple central nervous system (CNS) lesions. Because the condition most often occurs secondary to water deprivation (rather than a primary toxic intake of salt), salt poisoning is frequently apparent at a “pen” or “herd” level. Signs include aimless wandering, blindness, deafness and head pressing. Affected pigs sometimes “dog-sit”, slowly raise their nose upward and backward, and fall on their side in spasms that may be followed by paddling of the legs. They then may arise and continue their wandering.
Diagnosis associated with water deprivation may be suggested by history, signs, and elevated sodium levels in serum or cerebrospinal fluid. Gross lesions may be absent or limited to gastroenteritis. Gastroenteritis is more likely in pigs consuming salty brine and may be accompanied by diarrhea. A valuable but not infallible diagnostic aid is the microscopic observation of rather unique meningeal and cerebral perivascular cuffing by eosinophils in brain. Later and less reliably there may be laminar subcortical polioencephalomalacia or necrosis. Salt poisoning must be differentiated from all other encephalitic diseases. In an affected pen, a clue to the occurrence of water deprivation will be the absence of any urine or wet feces on the pen floor.
Water-deprived or affected pigs should be reintroduced to water slowly, given only small amounts of water at frequent intervals. This may suppress mortality. Pigs showing clinical signs usually die regardless of treatment.