At Legend, we require all of the puppies sold out of our breeding program to stay intact until two years of age, whether a pet, service dog or hunting dog. We have found that whenever a dog is spayed or neutered it cuts off their endocrine system development, effectively stopping all adult hormones from continuing to develop. This lack of adult hormone locks your dog in, mentally and emotionally at whatever age you spay or neuter them. This means that if you have a hyperactive 4 month old puppy at the time of spay, you will have a hyperactive, silly puppy for the remainder of your dog's life. Allowing our dogs to become fully sexually mature, means that we are also allowing them to become fully emotionally mature. In addition, a dogs skeletal structure is not fully developed until two years of age. Spay and neuter prior to the age of two causes delayed growth plate closures. And because dogs grow in spurts, length, then width, then height, then start over again with length, width and height; if a dog's growth plates delay to close this causes the dog to continue to grow in height, but without the width and length spurts to match it. This long term produces a dog that is very tall and lean with minimal muscling or bone density to match it's height. As a professional I can often look at a dog and guess at what age it was neutered based upon the growth patterns of the dog. Outside of emotional maturity, this is an exceptional article that focuses on the effects of early spay and neuter to the physical development of your dog.
We hope that we have given you some valuable information to consider in the spay and neuter debate of your companion!