The overwhelming majority of companion dogs in the United States are sterilized (neutered/spayed), most before one year of age. Neutering is critically important for population control, reduction of some reproductive disorders, and offers convenience for owners. Most pet parents (and some veterinarians) assume there is one method of sterilization for male dogs. In fact, there are several, but only two that I recommend.
- Castration (also known as neuter and gonadectomy), is the most common sterilization procedure in the US for male dogs. In this procedure, the testes (gonads) of the dog are removed. Any surgery that removes the gonads changes the animal in both positive and negative ways. In addition to population control, castration prevents testicular cancer and can minimize sexually driven behaviors. However, there is mounting evidence supporting the long-term health complications associated with surgical sterilization with gonad (testes) removal. Gonads are not just sex/reproductive organs; they are necessary endocrine glands for normal metabolic, behavioral, musculoskeletal, and anti-neoplastic (tumor/cancer) health.
The risks/disadvantages associated with castration include:
- Higher risk of joint disorders - Several studies show that neutering in the first year of life increases the risk of debilitating joint disorders. For example, in a study which examined the medical records of German Shepherd dogs examined over a 14.5-year period, 7% of intact males were diagnosed with a joint disorder, versus 21% of male dogs neutered prior to one year of age. Joint disorders such as hip dysplasia, cranial ligament tear or rupture (CCL) and elbow dysplasia are among the most common.
- Higher risk of cancer – A study of Golden Retrievers found that neutering at any time through 8 years of age increased the risk of osteosarcoma, hemangiosarcoma, lymphoma and mast cell tumors by 3-4 times. One study showed significantly higher rates of prostate carcinoma, prostate adenocarcinoma, prostate transitional cell carcinoma, and urinary transitional cell carcinoma in neutered dogs versus intact dogs. 
- Higher risk of developing autoimmune diseases – Studies suggest that castration is associated with an increased risk for certain autoimmune disorders. The reproductive system and the immune system are highly interdependent. Diseases such as atopic dermatitis, irritable bowel disease (IBD), autoimmune hemolytic anemia (AIHA), canine immune-mediated thrombocytopenia (ITP), pemphigus complex (PEMC), have been shown to present 2-4 times more than intact dogs.
- Changes in behavior – Castration has been advocated to make dogs more well-behaved companions. However, several studies have reported that castration neither prevents nor reduces dogs’ aggressive behavior. While some studies suggest that castrated male dogs were significantly more likely than intact dogs to have bitten a person, other studies seem to suggest that castration prevents or improves the aggressive behavior of dogs.
Vasectomy is a less invasive procedure performed under general anesthesia. It involves cutting or tying the Vas Deferens, which transports sperm. The testes remain intact, but the dog is rendered infertile because the sperm is prevented from being ejaculated during copulation. This surgery can be performed on pediatric patients (dogs <6 months) without interfering with pubertal maturation. Keeping the sex hormones intact significantly reduces the risk of the joint disorders and cancers that can occur with castration. Studies also show a reduced incidence of obesity as well as adverse reactions to vaccines
The risks/disadvantages associated with vasectomy include:
- Vasectomy is not effective right away. Dogs should be prevented from roaming or having contact with intact female dogs for 2 to 6 months following the procedure.
- Higher risk of testicular cancer – Just as with intact dogs, dogs rendered infertile by a vasectomy have some risk of developing testicular cancer.
- Disorders of the prostate – There is an increased risk of developing problems such as prostatitis (a bacterial infection), benign prostatic hyperplasia (non-cancerous enlargement of the prostate), prostatic cysts, and squamous metaplasia of the prostate (non-cancerous estrogen-producing tumors), although none of these are cancerous disorders.
- Increased risk of hernia – Incidences of perineal (scrotum and anus) and inguinal (groin) hernia, as well as perineal adenoma (tumors in the anal region) are higher in dogs sterilized by vasectomy versus castration.
- Behavioral concerns - Although the dog is infertile, he will continue to have interest in females in heat. Taking him into public spaces may be a challenge as he will appear to be intact. There is also an increased risk of wandering and urine marking. There may be a risk of inter-dog aggression due to competition for available territory or availability of females in heat. Good training can solve all of these issues.
Should I leave my male dog intact?
As with any procedure, there are risks associated with sterilization as well as leaving your male dog intact. Not all dogs have health problems after spaying or neutering. Unfortunately, in some dogs, neutering can greatly increase the chance of serious health problems. These risks depend on breed, age at the time of sterilization, size, sex and genetics. Pet owners should know the pros and cons of these procedures in the context of their own dog and discuss these options with their veterinarian.