In this section we will present the developmental orthopedic joint disorders early spay/neuter produces. At the heart of the matter is how spay/neuter affects the dog’s hormones. When a dog’s reproductive organs are surgically removed, the “sex hormones” they produce in large part disappear, at least temporarily. The sex hormones are responsible for more than just sexual behavior, and one of their responsibilities is regulating growth.60,61,89,108
Sex hormones direct the closure of growth plates on long bones. To the extent spay/neuter disrupts the production of sex hormones in an individual dog, it will delay the closure of growth plates on the long bones, provided the spay or neuter occurs before the growth plates have closed.61,108 The closure of bony growth plates generally occurs when the dog is between the ages of 4 and 18 months. Unfortunately, for the most part neutering (or spaying) is being performed prior to 6 months of age as advocated by many veterinarians and animal activists.
In 2014, UC Davis released research which allows us to amplify the findings of the 200783 systematic review referred to in our Research, Spay and Neuter sections of this site. The 2014 study 61 acknowledges that in the last three decades, the practice of spaying female dogs and castrating males (both referred to in this study as neutering) has greatly increased. Generally, spay/neuter is advocated prior to 6 months at UC Davis. A 2008 study 89 concludes that the prevalence of hip dysplasia and cranial cruciate ligament tear have also increased over the last four decades.
The aforementioned 2014 UC Davis study combined the incidence of all three joint disorders that have shown evidence of being increased by spay/neuter (i.e., hip dysplasia, cranial cruciate ligament tear, and elbow dysplasia) for one data-point representing the incidence of dogs diagnosed with at least one of the joint disorders. This analysis was also deemed logical for pathophysiological reasons because a disruption of the growth plate closure by gonadal hormone removal in the joint developmental stage would be expected to apply to all the joint disorders.
In fact, the 2014 UC Davis study showed that in Labrador Retrievers, about 5 % of the sexually intact males and females had one or more joint disorders. Spay/neuter at less than 6 months doubled the incidence of joint disorders in both sexes.
In Golden Retrievers, the sexually intact males and females had the same 5% incidence of one or more joint disorders. However, spay/neuter at less than 6 months increased the incidence of joint disorders to 4-5 times that of intact dogs.61
In 2016, a UC Davis produced study of German Shepherds reveals that in males and females, neutering or spaying within the first year of life is associated with a highly significant, threefold risk of acquiring at least one joint disorder.108
Briefly, spay/neuter delays the closure of growth plates on long bones, provided the spay or neuter occurs before the growth plates have closed.61,108 The closure of bony growth plates generally occurs when the dog is between the ages of 4 and 18 months. The variability with respect to dogs developing any one of these disorders, or all three, is dependent upon the time frame chosen for the spay/neuter and the actual genetically determined time frame for closure of growth plates in the individual dog.
Because these orthopedic disorders are so often associated with obesity rather than spay or neuter within the veterinary community, it bears mention that the interim findings in the Golden Retriever Lifetime Study (GRLS) show a strong connection between spay and neuter, obesity, and orthopedic injury. At the Aug 21, 2018 Fetch dvm360 conference in Kansas City, Missy Simpson, DVM, PhD, epidemiologist for the Morris Animal Foundation’s GRLS presented. She reported compared to intact dogs, dogs that underwent gonadectomy (spay or neuter) when they were 1 year old or younger faced a two-times higher risk for overweight or obesity. Dogs older than 1 year had a 40% increased risk for overweight or obesity. Further, Dr. Simpson shared that for every year older the dog was when gonadectomy occurred, it reduced the risk of overweight and obesity by 70%. Additionally, overweight or obese dogs that had undergone gonadectomy showed a 300% increased risk of chronic non-traumatic orthopedic injury (osteoarthritis, cranial cruciate ligament disease). Dr. Simpson says veterinarians should share with owners that if they keep their dogs lean, owners can reduce the risk of these orthopedic problems by almost half. We see the take-home message differently: if you do not spay or neuter your dog (instead provide tubal ligation or vasectomy) your dog will have a greatly reduced likelihood of obesity, and a greatly reduced incidence of orthopedic injury.