You have not given complete details about your dog like he does not eat dog food only or he is not eating any thing. Sometimes, dogs refuse to eat because they don't like specific food. If your dog is not eating any food since last 24 hours then take him to vet because loss of appetite can be one of signs general illness. Following are diseases and conditions that can cause loss of appetite in dogs.
1. Diseases of Kidneys
2. Pain
3. All diseases of digestive tract which includes esophagus, stomach, intestine, pancreas, and liver
4. Blood diseases
5. Skin diseases
6. Diseases of brain
7. Mouth and throat diseases
8. Nose diseases
9. Eye diseases
10. Depression
11. Anxiety
If your dog is not eating only dog food then change his food. Otherwise take him to vet.
1. Diseases of Kidneys
2. Pain
3. All diseases of digestive tract which includes esophagus, stomach, intestine, pancreas, and liver
4. Blood diseases
5. Skin diseases
6. Diseases of brain
7. Mouth and throat diseases
8. Nose diseases
9. Eye diseases
10. Depression
11. Anxiety
If your dog is not eating only dog food then change his food. Otherwise take him to vet.