Testicular tumors are among the most common cancers in intact male dogs, yet are almost entirely preventable through castration, making this welfare consideration a strong argument for neutering in dogs not intended for breeding.
Testicular cancer welfare includes both the tumor itself and, for hormone-producing tumors, the serious secondary effects of estrogen on bone marrow function. Aplastic anemia from Sertoli cell tumor estrogen production is a potentially fatal welfare emergency that requires emergency castration and blood support. The fact that castration provides essentially 100% prevention of this cancer makes it one of the most compelling welfare arguments for the procedure in dogs not intended for breeding. Cryptorchid dogs face even higher risk and should be castrated as soon as they are old enough for anesthesia.