* Hip dysplasia: This is a condition in which the hip joint does not develop properly, leading to pain, lameness, and arthritis. It is more common in large breeds of dogs, such as German Shepherds, Golden Retrievers, and Labradors.

* Osteosarcoma: This is a type of bone cancer that is more common in large dogs. It is often aggressive and can spread to other parts of the body.

* Bloat (gastric dilatation and volvulus): This is a life-threatening condition in which the stomach twists on itself, trapping gas and fluid inside. It is more common in large, deep-chested breeds of dogs, such as Great Danes, Weimaraners, and German Shepherds.

* Cruciate ligament rupture: This is a tear in the cruciate ligament, which is a band of tissue that connects the shin bone to the thigh bone. It is more common in large, active dogs, such as Labrador Retrievers, Golden Retrievers, and Rottweilers.

Small dogs

* Dental disease: This is a common problem in small dogs, especially those with short noses, such as Pugs, Bulldogs, and Shih Tzus. Dental disease can lead to pain, infection, and tooth loss.

* Kidney disease: This is a common problem in older small dogs, especially those with diabetes or high blood pressure. Kidney disease can lead to failure, which is fatal.

* Liver disease: This is a common problem in small dogs, especially those that are overweight or eat a high-fat diet. Liver disease can lead to failure, which is fatal.

* Hypothyroidism: This is a condition in which the thyroid gland does not produce enough thyroid hormone, which is essential for metabolism. Hypothyroidism is more common in small breeds of dogs, such as Poodles, Cocker Spaniels, and Dachshunds.