XL American Bully: Height, Weight, Lifespan, Health & Nutrition The XL American Bully is the largest recognised size variety of the American Bully. It is a powerful, muscular and substantial dog, but responsible breeding and ownership should focus on soundness, mobility, breathing and overall health—not simply producing the biggest possible dog. The UKC’s current breed standard specifically warns that quality should not be sacrificed for size and mass and discourages exaggera