Dehydration can be caused by numerous illnesses or abnormalities and can be divided into two main categories: reduced fluid intake or increased fluid losses.
Reduced Fluid Intake
The body relies on a steady intake of fluid to maintain hydration. When the ingestion does not meet the body demands, dehydration occurs. If your pet is not eating or drinking adequately because of disease or illness, dehydration is likely to occur. Reduced fluid intake can also occur if there is either accidental or deliberate deprivation of food or water. If you leave your pet unattended for several days and he spills his water bowl, he may be without water for several days.
Increased Fluid Losses
In some diseases or illnesses, your pet may be able to consume enough fluid to meet body demands. The most common cause of this is vomiting and diarrhea or kidney disease. With vomiting and diarrhea, excess fluids are lost. In kidney disease, the kidneys are unable to conserve fluids and they excrete excess fluid in the urine. Other causes of increased fluid losses include excessive panting, fever, large wounds or burns that ooze fluid or severe prolonged drooling.