A significant and sudden decrease in weight accompanied by weakness is considered an unhealthy weight loss in your pet. Being slightly thin is actually a benefit for your pet, as thin pets tend to live longer than overweight pets, but unhealthy weight loss that happens quickly is a sign that your pet could be sick.
Because 2/3 of your pet's body is water, sudden weight loss may be caused by dehydration rather than by loss of fat. Under some circumstances, your pet becomes dehydrated and loses weight too. It's important to understand which is happening because dehydration quickly leads to death. Unhealthy weight loss slowly leads to death.
Pets with dental disease often lose weight because eating is painful. In addition, bacteria in their mouths spread over the body and cause disease in the kidneys, liver, and heart. Disease of major organs often leads to weight loss.
Pets with worms lose weight, but for different reasons. Pets with intestinal worms have the nutrients sucked out of them. Pets with heartworms waste energy as their hearts no longer contract efficiently. Their lungs, where worms also reside, no longer have normal blood flow. In pets with heartworm infections, the kidneys and liver work harder than normal to help the body respond to constant parasite abuse.
Pets with a disease in vital organs, including in the heart, lungs, kidneys, liver and spleen, often lose weight. Functioning of these organs is essential to sustain life. When these organs are compromised, the rest of your pet's body doesn't function well either. A poorly functioning metabolism creates a large energy drain, and your pet often metabolizes fat and eventually muscles to sustain life.
Cancerous pets lose weight for several reasons. Many cancers demand nutrients and rob the body of nutrition so that fat and muscle tissue disappears. In addition, cancer often stimulates the liver to make tumor necrosis factor (TNF). TNF resets the body's thermostat so that all cells consume more energy than normal. TNF also affects the body so the pet feels sick and doesn't want to eat. This anorexia is characteristic of most cancers.
These pets lose weight for the same reasons that pets with cancer lose weight: TNF is stimulated. The body's thermostat is set higher, which is why pets with infections have fevers, and most are anorexic. In addition, pets with infectious diseases are often given medications that cause nausea and loss of appetite.
A burned pet loses weight due to several factors: pain, stress-induced ulcers, medication affecting the stomach and intestines, and depression. Pets with burns have lost the skin's barrier to infectious bacteria and are often overwhelmed with infections. The immune system revs as if it is launching a Saturn missile, using an incredible amount of energy, but is not always able to save your pet's life.
Aging pets lose weight because they often have nagging pain from arthritic joints and dental infections. They also experience weakening of vital organs. In addition, senior pets do not smell or taste their food as they had. They may suffer from confusion and depression.
If your pet is depressed, he or she does not have the spirit to eat. Pets can become depressed and lose weight when a family member dies, when they can't engage in the sports they loved, or climb on the bed.