You should be able to feel individual ribs, but not see the definition of each rib. This is a good rule of thumb. If you don't feel his ribs, it means you're overfeeding him. If you see visible ribs, then your dog is truly hungry and needs more food.
How do I know if my dog needs more food?
As a general rule, a dog that increases his activity level will require more food and water. The best way to gauge this is to keep an eye on your pet's body index; if he or she seems to be gaining or losing weight with changes in his/her diet and activity level, you may need to adjust what you're feeding.
How long until a dog gets hungry?
Because dogs have a simple stomach structure, once the stomach is filled with food, it will empty within a few hours as food moves into the small intestine. After 8 to 10 hours, an empty stomach begins to send signals to the brain stimulating a hunger response.
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