Some dogs infected with virus can cause weakness, loss of appetite and other symptoms, which in turn affects weight gain. For example, canine distemper is a common disease in dogs. Sick dogs often have symptoms such as listlessness, loss of appetite, vomiting, and even diarrhea and respiratory symptoms in severe cases. All these will lead to the dog's weight not increasing but decreasing. In addition to canine distemper, other viral infections, such as canine nephritis virus infection and canine infectious laryngitis, can also cause dogs to lose weight without gaining weight.

2. Parasitic infection

Parasitic infection is also one of the reasons why dogs lose weight. There are many kinds of parasites in dogs, such as roundworms, hookworms and tapeworms. Parasites parasitize in the host to obtain nutrition, which leads to emaciation, loss of appetite and unwillingness to eat, thus affecting its weight gain. In order to prevent parasitic infection in dogs, owners need to regularly deworm dogs to ensure their health.

3, digestive system diseases

Dogs with digestive diseases can also keep them from getting fat. For example, when dogs suffer from gastroenteritis, gastrointestinal ulcer, enteritis and other diseases, they often have symptoms such as loss of appetite, vomiting and diarrhea, which affect the absorption and utilization of food and lead to emaciation. At this time, the owner should take the dog to the veterinarian in time to treat the disease and ensure the dog's health.

4. Immune system diseases

Dogs with immune system diseases will also gain weight. Immune system diseases will lead to decreased immunity, and the metabolism in dogs will also decrease accordingly, which will lead to loss of appetite and weight loss. There are many kinds of immune system diseases, among which autoimmune hemolytic anemia and anemic canine tumor are the most common. The breeder should take the dog to the vet for treatment in time.