One of the most common questions we discuss with new dog and cat owners is when to spay or neuter their pet.
Backing up just a bit, the word “neutering” refers to a surgical procedure that renders the animal sterile, both male and female. “Neutering,” however, has come to be associated more with the procedure in male dogs (i.e. castration) rather than female dogs; “spaying,” on the other hand, refers to sterilization by removal of the reproductive tract in female dogs. For our purposes, we will use “neutering” to refer to the procedure in males dogs and “spaying” for female dogs.
Traditionally, most veterinarians in the U.S. have been taught that early spaying and neutering is the best medicine for our canine and feline patients. However, this has recently become a controversial topic in veterinary medicine.
“Early” has typically referred to younger than six months, or pre-puberty, though often dogs and cats are spayed or neutered as young as seven to eight weeks. The advantage of early sterilization have been touted as:
- Fewer unplanned pregnancies and therefore fewer unwanted and homeless pets. This is a VERY important reason for sterilization.
- Decreased risk of prostatitis (infection or inflammation of the prostate).
- Decreased risk of mammary cancer in female dogs and cats. After the first heat cycle in a female dog, the risk of mammary cancer goes up to 8 percent, after two heat cycles it increases to 26 percent. (Most mammary cancers in cats are malignant and about half of mammary cancers in dogs are malignant.)
- Eliminate risk of uterine, ovarian, vaginal or testicular cancers.
- Eliminate risk of pyometra (a hormonally influenced, severe and often life-threatening uterine infection) in female dogs and cats.
- Decreased risk for perianal adenomas (a benign skin tumor around the anus).
- Less roaming, especially among male dogs. This is specific to an individual’s containment set-up. However, the No. 1 risk factor for a dog to be hit by a car is to be an intact male.
- Improved behavior/less aggression. Spaying or neutering can decrease some behavioral habits or aggressive tendencies, especially when inter-dog related. However, most cases of behavioral and aggression problems are not due to sex hormones.
- Less marking behavior in male dogs and cats. There may be some truth to this, especially with cats, though often marking is a behavior issue in dogs and not dominated by sex hormones.
- Spayed and neutered dogs live longer.
Recently there has been talk among veterinary professionals about whether early spay/neuter is all it’s cracked up to be — and that perhaps there are even some risks associated with the early spay and neuter of dogs (i.e. before sexual maturity and generally considered less than 6 months of age). The potential risks of early spay and neuter include:
- Increased propensity to obesity
- Increased risk of cranial cruciate ligament disease (the dog version of an ACL tear) in large and giant breed dogs.
- Increased risk of hip dysplasia in large and giant breed dogs
Increased risk of urinary incontinence, especially in female dogs.
- Increased risk of some types of cancer, including:
- Lymphoma — a cancer of a specific type of white blood cell.
- Hemangiosarcoma — a highly malignant cancer of blood vessels.
- Mast cell tumors — a potentially malignant cancer of the skin.
- Osteosarcoma — a highly malignant cancer of bone.
- Transitional cell carcinoma — an aggressive cancer of the bladder or urinary tract.
There is little research reviewing the risks of pediatric spay/neuter in cats. However, cats sexually and skeletally mature at a younger age than most dogs which may be why there are few documented concerns with risks of early spay/neuter. Observationally, we see an increase in propensity for male cats to develop urethral obstruction (they can’t pee) if they were neutered well before sexually maturity and have an underdeveloped (small, with a very small urethral opening) penis.
When a pet is sterilized, the sex hormones, such as testosterone, estrogen and progesterone, are removed as well. It is well-documented that removal of these hormones slows metabolism, leading to the propensity for obesity. Removal of these hormones is also thought to speed bone growth (the sex hormones have an inhibitory or slowing effect on bone growth and joint development) in young animals, leading to increased cruciate ligament injury and hip dysplasia. The increased risks of some cancers are also thought to be related to lack of these sex hormones, which likely have an inhibitory effect on certain types of cancer.
As you can already see, it’s certainly not a clear-cut decision and population control is a very real and needed thing. Additionally, to further confound things, scientific studies in veterinary medicine are not nearly as robust as those on the human side. We are lucky if there are 200 dogs in a study, and often is it much fewer. Many of the studies looking at the risks were done using purebred large and giant breed dogs — so we have to take all of the results with a grain of salt.
Fortunately, there is a large study in golden retrievers underway, being conducted by the Morris Animal Foundation, looking at more than 2,000 dogs over the course of the lifetime. This should provide us with an abundance of information not only about the benefits and risks of early spaying and neutering, but of spaying and neutering in general.
So, what is the best protocol? The answer depends on the breed/size, sex and species of your pet, and what your intended plans are for your pet. For example, a 20 pounds Shih Zhu, who is not nearly as at risk for CCL injury or hip dysplasia, nor several of the aforementioned cancers, would be a good candidate for neutering between 6 to 9 months of age, or spaying around 6 to 7 months of age. Whereas, a great Dane puppy who may reach 140 pounds or more as an adult and is much more prone to orthopedic issues would be a better candidate for neutering at 12-18 months of age (near or after skeletal maturity) and spaying at 9 to 12 months of age (after the first heat cycle, but before the second).
Additionally, many localities within the state of Virginia have a legal requirements for all pets adopted from shelters/rescue groups be sterilized or a signed agreement for sterilization within a specific time frame.
There is no one protocol that suits each and every pet and owner, so it is important to discuss thoroughly with your veterinarian. We also have to remember that even with all the information we have and are still gathering. So many other individual conditions, environmental factors, dietary factors, genetic predispositions and on and on and on, will influence an individual’s outcomes to a very large degree, and likely much more than the age of sterilization.