Benjamin Hart, a professor emeritus at the UC Davis School of Veterinary Medicine, did a comprehensive studyon health issues in mixed breed dogs weighing 44 pounds and over. He found that if these dogs were spayed or neutered prior to one year their health risks increased.

The study analyzed 15 years of data from thousands of dogs at the UC Davis Veterinary Medical Teaching Hospital. They found that joint disorders including hip dysplasia, elbow dysplasia and cranial cruciate ligament tears, and knee injuries jumped from 4% in intact dogs to 10 – 12% in those neutered or spayed prior to one year.

The problem which the study pointed out, is that when someone adopts or purchases a mixed breed dog as a puppy, they may not know who the parents are and thus will not know for sure how big the dog will get as an adult.

In an earlier study, the scientists determined that health risks due to the age of neutering varied a lot depending upon the breed of dog. In this case the common belief that a mixed breed dog is generally healthier than a purebred does not seem to be the case.

My question is, why is there a difference between mixed breed and purebred if the injuries are a result of weight.

The bigger issues as pointed out in the article is that the common practice of early spay and neuter needs to be reviewed and possibly modified. This is also important information for people who train working dogs.