If you have already spayed or neutered your pet you probably don't want to read this, but if you haven't read on:
Viable options are a vasectomy for a male and a partial spay for a female. However, many veterinarians may resist this as all changes are slow in coming. One of these papers states a high percentage of intact female dogs dying of pyometra which is why the partial spay is probably best for the female dog. Some vets talk about the stress of the female heat cycle, but with the Havanese, at least my Havanese, there is little change in behaviour during a heat cycle.
