The approach of when to spay or neuter your pet has been controversial, and in some cases, is influenced by the country where you live. It’s understandable why animal shelters and humane societies have embraced early spay-neuter programs, whose goal is to reduce the unwanted overpopulation of unowned dogs. But is that what’s best for the dog, from an orthopedic point of view?
Recently, a study was published from the University of California-Davis that addressed this issue in 35 breeds of dogs. Although the article also addressed cancer and urinary incontinence, I will focus on the joint conditions in this blog. Specifically, they looked at the most common developmental joint problems, including hip dysplasia, cranial cruciate ligament disease, and elbow dysplasia. They pointed out that previous studies have shown that spaying or neutering Golden Retrievers, Labrador Retrievers, and German Shepherd Dogs before 1 year of age was associated with a 2-4 times increased risk of joint disorders compared to intact dogs. The risk was especially pronounced if they were altered by 6 months of age. Wow!
In this study they looked at other breeds, including small breeds of dogs. They evaluated medical records of the selected breeds and looked at the information for dogs that were neutered or spayed at less than 6 months, 6-11 months, 12-24 months, 2-8 years, or left intact. Conditions were tracked until their last hospital visit, or until 11 years of age.
Fortunately, for the little guys, there was no apparent increase in joint problems with early spay/neutering. But smaller breeds generally do not have a high prevalence of hip dysplasia, elbow dysplasia or cranial cruciate ligament disease in any case. They are most susceptible to luxating patellas and Legg-Calve-Perthes disease (for more information on these conditions, click over to the My Lame Dog tab on MyLameDog.com, and go to the various joints). Breeds where spaying and neutering apparently made little difference in joint disorders include Australian Shepherds, Border Collies, Boston Terriers, Boxers, Cavalier King Charles Spaniels, Chihuahuas, Collies, Corgis, Dachshunds, English Springer Spaniels, Jack Russell Terriers, Malteses, Miniature Schnauzers, Pomeranians, Toy Poodles, Standard Poodles, Pugs, Shetland Sheepdogs, Shi Tzus, West Highland White Terriers, and Yorkshire Terriers.
There were gender differences in some breeds. Australian Cattle Dogs had increased risk of joint disorders in females spayed at <6 months, but males were not affected. Male Beagles and Cocker Spaniels neutered early had increased risk, but not females. Male Miniature Poodles had more cranial cruciate ligament disease if they were neutered between 6 and 11 months, but not females.
The story is different for the large and giant breeds, however. Bernese Mountain Dogs, Bulldogs (2-3 times increased occurrence of joint disorders with early spay/neuter, but this did not reach statistical significance), German Shepherd Dogs, Golden Retrievers, Labrador Retrievers, Rottweilers, and Saint Bernards all had increased risk of orthopedic conditions with early spay/neuter.
One positive point is that Great Danes and Irish Wolfhounds had no increase in joint conditions with neutering at any age, and for the most part, the same is true of Doberman Pinschers!
Why does neutering or spaying have an effect on most large and giant breeds of dogs? Most believe that the reason lies in the influence of sex hormones (estrogen and testosterone) on closure of growth plates. If dogs are spayed or neutered at any early age, the growth plates stay open longer, allowing bones to continue growing, and in some cases, it may alter the interaction of bones at joints. For example, dogs spayed or neutered at a young age tend to have a steeper slope of the tibial plateau, which may predispose to cranial cruciate ligament disease.
So why didn’t the age of spaying or neutering have any effect on Great Danes, Irish Wolfhounds, or Doberman Pinschers? In general, joint conditions are pretty uncommon in these breeds, as is the case with Greyhounds. What do these breeds have in common, at least for cranial cruciate ligament disease? They all have very angulated pelvic limb conformation. In other words, the standing stifle and hock angles are quite flexed. This likely results in a more level standing tibial plateau angle, which probably puts less stress on the cranial cruciate ligament. Other breeds have increasingly become more upright in the stifle joint, with a straighter standing angle. To further evaluate these situations, let’s look at two dogs; one has a very angulated pelvic limb, and the other is quite straight. Let’s say that the slope of the weight bearing tibial surface of the stifle is the same in both dogs relative to the entire shaft of the tibia. This sloped surface, known as the tibial plateau angle, is measured with a radiograph. Now, when the dog with greater angulation of the limb is in a standing position, the slope of the tibial plateau surface will be more parallel with the ground. On the other hand, the dog with the straighter standing pelvic limb conformation will have a relatively steeper tibial plateau surface relative to the ground. Therefore, there will be more chronic force placed on the cranial cruciate ligament to provide stability to the joint, eventually resulting in ligament damage. Confusing? Maybe a bit, but these are my observations in doing surgery on dogs with cruciate ligament rupture over the last 30 years.
Now, every study has its weaknesses, so what are they in this study? The standard for making recommendations is a meta-analysis of several prospective, randomized, blinded studies. So, what does that mean? Ideally, a study would take a large number of litters of puppies of a particular breed, and randomly assign them to be spayed or neutered at different ages. The dogs should then be followed for at least several years, if not a lifetime, with appropriate assessments during these times. So, you can see such research is time-consuming, and expensive. Several of these similar studies would be needed to pool them into a larger meta-analysis that would look for consistent patterns in all of the individual studies. Unfortunately, in veterinary medicine, funding for such studies is very limited, and long-term studies are even harder to find. So, we often have to make the best of things. In this study, they evaluated medical records from the university veterinary hospital. This was a retrospective study, which is generally a weaker study design than a randomized, prospective, blinded study, but nevertheless, valuable information can come from these types of studies, as is the case here. Another potential weakness is that the diagnosis was made on dogs that were presented with clinical signs, usually lameness, difficulty moving, or joint pain. They then examined the dogs and performed radiographs or surgery. It is quite possible the various conditions were underdiagnosed, since many dogs with subclinical disease are never examined. Further, there are some studies that suggest owners of spayed or neutered animals are more likely to seek veterinary care than those with intact animals, which may increase the number of spayed or neutered dogs with a diagnosis of joint disease. Also, unlike other studies that have suggested an association of body condition scores with orthopedic conditions, because they found no such association with their previous study of retrievers and German Shepherd Dogs, they did not evaluate body condition score in this study.
So, what’s the bottom line? Based on this study, other similar studies, and clinical experience, it makes sense to avoid spaying or neutering large and giant breeds of dogs until they are sexually mature. It probably does not apply to smaller breeds of dogs, but the influence of sex hormones on the growth and development of the femur and tibia have not been sufficiently analyzed to see the effects on development of patella luxation, one of the most common orthopedic conditions in small breeds. However, even though these studies seem logical, until we have adequate prospective studies as detailed above, we should proceed with caution in making firm judgements and conclusions.
If you want to delve further into the details of the study, it is an open access journal, meaning that it is available to anyone at no charge. It may be accessed from Frontiers in Veterinary Science.
Hart BL, Hart LA, Thigpen AP and Willits NH (2020) Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence. Front. Vet. Sci. 7:388. doi: 10.3389/fvets.2020.00388
Abstract
Neutering (including spaying) of male and female dogs in the first year after birth has become routine in the U.S. and much of Europe, but recent research reveals that for some dog breeds, neutering may be associated with increased risks of debilitating joint disorders and some cancers, complicating pet owners’ decisions on neutering. The joint disorders include hip dysplasia, cranial cruciate ligament tear or rupture, and elbow dysplasia. The cancers include lymphoma, mast cell tumor, hemangiosarcoma, and osteosarcoma. In previous studies on the Golden Retriever, Labrador Retriever and German Shepherd Dog, neutering before a year of age was associated with increased risks of one or more joint disorders, 2–4 times that of intact dogs. The increase was particularly seen with dogs neutered by 6 months of age. In female Golden Retrievers, there was an increase in one or more of the cancers followed to about 2–4 times that of intact females with neutering at any age. The goal of the present study was to expand and use the same data collection and analyses to cover an additional 29 breeds, plus three varieties of Poodles. There were major breed differences in vulnerability to neutering, both with regard to joint disorders and cancers. In most cases, the caregiver can choose the age of neutering without increasing the risks of these joint disorders or cancers. Small-dog breeds seemed to have no increased risks of joint disorders associated with neutering, and in only two small breeds (Boston Terrier and Shih Tzu) was there a significant increase in cancers. To assist pet owners and veterinarians in deciding on the age of neutering a specific dog, guidelines that avoid increasing the risks of a dog acquiring these joint disorders or cancers are laid out for neutering ages on a breed-by-breed and sex basis.