The normal behavior of a dog is often incompatible with being a household pet. Intact dogs tend to wander from home, seeking a mate or defending their territory. This puts them at risk for being hit by a car or being injured in a dog fight. Urine marking and some types of aggression are more pronounced in non neutered dogs as well. Although neutering may not entirely eliminate these behaviors, it can diminish them by 50-90%.
Intact male dogs suffer from a high incidence of inflammation and enlargement of the prostate, as well as testicular tumors. Older dogs commonly develop swollen and infected prostate glands. These conditions are painful and can interfere with urination and defecation. After neutering, the prostate shrinks considerably. Tumors of the testicles, common in older intact male dogs, are eliminated entirely.
The effects of neutering on your dog will not be instantaneous. Testosterone levels wane over a period of weeks or months, followed by a reduction in fertility and territorial and mating behaviors.