by DREW MCWATTERS, DVM
Veterinarians have traditionally recommended universal spaying and neutering of dogs and have advised doing it at no later than six months of age. This recommendation came from a desire to decrease the stray pet population and decrease the incidence of reproductive disease while at the same time decreasing anesthetic risks associated with anesthesia of young puppies.
However, several recent studies have called into question whether this really is the best practice. These studies have showed impacts of spaying and neutering (both positive and negative) on four general areas of health: weight, orthopedic disease, cancer, and urinary health. I’ll give you the general findings in each of these areas and then give you my recommendation on how we practically apply this information to your dog.
Spaying and neutering have long been implicated in weight gain and the studies confirmed there is moderate increase in the risk of obesity for dogs who have been spayed and neutered. However, the studies did not show the age of spaying or neutering to change the risk of obesity.
It is also important to note that while spaying and neutering decrease metabolic rate, environmental factors such as lack of exercise and excessive calorie intake play much bigger roles in the obesity epidemic and dogs who have been spayed or neutered will still maintain a healthy weight if fed and exercised appropriately.
This may be the area with the most clearly defined risks and benefits. It is well documented that spaying and neutering before skeletal maturity is reached (before the growth plates have closed) will delay closure of the growth plates which will result in disproportionately long limbs. This changes the stress and load on the joints which increases the risk of orthopedic diseases such as cranial cruciate rupture (an ACL tear) and hip dysplasia. This risk is most dramatic in large and giant breed dogs (adult weight over 50 pounds) considering they are already more at risk for orthopedic disease and their growth plates close at a later age than smaller dogs.
Because of this, we recommend large and giant breed dogs wait to be spayed or neutered until they reach skeletal maturity (generally between 12-15 months of age).
If orthopedic disease had the most clearly defined risks and benefits, the role spaying and neutering spays in cancer may be the hardest to define, especially the risks. We have long known that uterine infections, ovarian, vaginal, and testicular tumors are prevented by timely spaying or neutering. We know that spaying before the first heat cycle reduces the incidence of mammary cancer by 99.5% while spaying after the first heat cycle but before the second decreases the incidence by 92%. Spaying after the second heat cycle decreases the incidence rate by 74%. Spaying after the 3rd heat cycle provides minimal protection against mammary cancer. Spaying or neutering at any age removes the potential for uterine infections, ovarian, and testicular cancer by removing the organ that will be affected.
Where it gets complicated is cancers such as hemangiosarcoma (blood vessel cancer of the liver and spleen), osteosarcoma (bone cancer), and lymphoma show a mild to moderate increase incidence in dogs who are spayed and neutered, regardless of the age when they were spayed and neutered.
Dogs who are neutered have a dramatic decrease in the incidence of benign prostatic hyperplasia (BPH), while spayed or neutered dogs show a mild increase in bladder inflammation and moderate increase in urinary incontinence.
So, what do we do with all this information…?
Veterinarians sift through information like this every day, often with conflicting conclusions, and determine the best recommendations for our patients. Research is ongoing and more studies are needed to confirm or refute what we know so far. While the data seems to suggest that spaying and neutering at any age may increase the risk for many conditions and diseases, it may not be that black and white. However, data consistently shows that spayed and neutered dogs have an increased longevity over intact dogs.
In my opinion, the orthopedic risks from early spaying and neutering are clear while the cancer risks are less clear. This is because:
- Orthopedic diseases are usually young to middle-aged dog problems and all the dogs in the studies would be equally susceptible to developing orthopedic disease in any case, and
- Cancer is generally a disease of older dogs and the spayed and neutered dogs tend to live to an older age that intact dogs. Because of this, the decreased incidence of cancer in intact dogs may be because of the fact that they don’t live long enough to develop cancer.
The age to spay or neuter can vary depending on the individual dog and dog’s health. In general, for small breed dogs (less than 50 pounds) we recommend spaying around 6 months. In large breed dogs (greater than 50 pounds) we recommend waiting until after skeletal maturity but before the second heat cycle (usually 12-15 months) in spaying female dogs or any time after skeletal maturity in male dogs. Some clients still choose to spay or neuter early for a variety of reasons. We are happy to comply with those requests. As with all medical decisions about your dog, we want to make sure you have as much information as possible before making the decision to spay or neuter.
Please talk to your Mercer Street Veterinary Hospital veterinarian about what is best for your puppy when it comes to spaying and neutering!