Vasectomisation is preferred to castration as it does not affect the dog’s health in any way at all whereas castration may. Vasectomy means tying off the sperm ducts of the testicles. Vasectomized dogs are rendered infertile but they will still have good libido and will indeed still mate. Vasectomy is sometimes requested for service dogs, where both breeding and castration is unwanted. Vasectomised dogs still have normal testosterone levels. Some breeders often want a teaser dog which can assist them in identifying heat in bitches. A vasectomized male may be very helpful in identifying bitches which normally show very little external signs of heat. Vasectomized males are ideal because there is no danger of unwanted pregnancies. Some breeders vasectomize young puppies to enforce breeding restrictions. It is extremely difficult, and in most cases impossible, to reverse a vasectomy. Sperm which are produced in vasectomised dogs cannot escape the testicles and can therefore only be removed by resorption inside the testicles.