A vasectomy eliminates successful breeding but it does not reduce any of the undesirable problems of the intact male since it does affect testosterone production or its distribution throughout the rest of the dog s body. When young puppies are sexually mounting their 7 and 8-week old litter mates this is because of androgen surges in their bodies. The same is true with aggressive behavior. The degree castration has on suppressing aggression varies between animals and the age at which it is done. Its effect is greatest if it is done before one year of age.
Male dogs can sense females in heat through pheromones.
These are airborne chemical attractants that are liberated from the female when she is cycling. They travel through the air for great distances. We grew up on a farm where the next closest house was over a mile away but when one of our female dogs was in heat, the males would come for miles from upwind, downwind, and crosswind. Pheromones are, to say the least, very effective stimuli. The problem with this reasoning was that many of us keep our dogs restricted in our homes, a kennel, or on a chain.