1. Malnutrition: Malnutrition in the growing period of dogs may lead to sternal deformity, thus making the sternum prominent.

2. Genetic factors: Some breeds and genetic factors may also lead to sternal protrusion, such as bulldogs and Boston terriers.

3. Environmental factors: The dog's living environment and lifestyle may also affect its sternal protrusion, such as lack of exercise and excessive exercise.

If your dog has symptoms of sternal protrusion, I suggest you take it to the vet in time for professional diagnosis and treatment. Veterinarians may suggest an appropriate diet and exercise plan, or carry out medication or surgery to help dogs control symptoms. At the same time, we can also consider providing dogs with adequate nutrition and proper exercise to help improve their health.