Selective breeding poses several risks for dogs, including raising the risk of developing heart problems, kidney disease, heating prostration, the inability to cool the body, hearing and vision problems and blood disorders. Selective breeding may also create emotional or neurological problems. Some breeds, such as Bull Terriers, have a tendency to chase their tails incessantly, while Scottish Terriers may lose muscular control when they are excited.
Selective breeding poses risks to small and large dogs. Smaller dogs are prone to high blood pressure and skeletal abnormalities such as misaligned kneecaps, which causes kneecap dislocation. Dogs of larger breeds may develop malignant tumors in their bones, as their abnormally high weight puts excess strain on their skeletal systems, and they are prone to orthopedic issues.
Problems also arise among dogs with certain accentuated features, like flat faces or wrinkled skin. Dogs with flat faces, like pugs and Pekingese, may have short and narrow nasal passages, which interferes with adequate breathing. Bloodhounds may develop eye problems from wrinkled skin around the eyes, while Chinese Shar-Pei and other breeds develop skin irritation and infections from wrinkles. Female bulldogs with abnormally narrow hips often deliver young through Caesarean sections.
Some breeds, such as Portuguese water dogs, Standard Poodles and Basset Hounds, have poor immune systems. Certain cancers emerge in dogs with selective breeding, as do organ problems and other maladies.