Antibiotics are primarily used to treat bacterial infections and do not directly affect shrinking tumors in dogs or other animals. Tumors are abnormal growths of cells, and their development and progression are typically unrelated to bacterial infections. Therefore, antibiotics are not effective in directly targeting or eliminating tumor cells. However, there are situations where antibiotics may be prescribed alongside tumor treatment. For example, in some cases, tumors can become infected or cause secondary infections, leading to inflammation and other complications. In such instances, antibiotics may treat the infection and help manage associated symptoms.