The traditional age for neutering is around 6 months of age and many veterinarians still recommend neutering at this age. Activity level and appetite do not change with neutering. A male dog should not gain weight or become less interested in activity post neuter. His interest will be reduced but if he is around a female dog in heat, he will become aroused by her. Mounting behavior often has roots in the expression of dominance and may be expressed by a neutered male in a variety of circumstances that are not motivated by sexuality.
Undescended testicles have an increased tendency to grow tumors over descended testicles.
They may also twist on their stalks and cause life-threatening inflammation. For these reasons, neutering is recommended for dogs with undescended testicles. Some exploration may be needed to find it thus there is often an incision for each testicle. The retained testicle is sterile and under-developed. If there is one descended testicle, this one will be fertile but since retaining a testicle is a hereditary trait, it is important that the male dog not be bred before he is neutered.