Deciding whether or not to spay or neuter your pet is a personal decision that requires a close examination of each individual animal. The issue is controversial, because the research pertaining to the effects of the procedure on dogs and cats is inadequate and conflicting. The procedure itself carries few risks, but the long-term health effects are not fully understood and differ among animals depending upon sex, age at operation and breed. The effects are both positive and negative, but all stem from the interruption of the production of sex hormones.
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Reproductive Health
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During spay or neuter operations, reproductive organs such as the testicles, ovaries and uterus are removed, completely eliminating the risk of cancer in those organs. The risk of testicular cancer in dogs is moderate in all breeds, but effective treatment options are available making it rarely fatal. On the other hand, the University of Minnesota Veterinary Medical Center claims that breast cancer is the most common cancer among female dogs, and spaying eliminates the risk. Breeds predisposed to breast cancer are boxers and dachshunds.
According to the National Animal Interest Alliance, there is no conclusive study that links prostate cancer to testosterone production in male dogs. The University of Minnesota and many veterinarians claim that neutering your animal reduces the risk of prostate cancer by shrinking the gland and thereby preventing infection, but further study is needed for conclusive evidence. According to the National Animal Interest Alliance, prostate cancer is uncommon in both intact and neutered animals, so neutering them to protect prostate health is impractical. Bouviers are the only breed recognized as having a genetic predisposition to prostate cancer.
Osteosarcoma
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The National Animal Interest Alliance estimates that one half of all dogs that are spayed or neutered will develop osteosarcoma (bone cancer), a disease that is often fatal. Normal levels of sex hormones in dogs and cats maintain bone health, and reduction in these hormone levels can cause bone health to decline. Certain breeds, such as Rotweilers, have an increased risk of developing the disease. Risk increases with height, so all tall dogs are at higher risk. Risk increases again if the operation occurred before age 1. Spaying and neutering breeds that are predisposed to osteosarcoma further the risk that your pet will develop this debilitating disease. Intact animals rarely develop osteosarcoma.
Hypothyroidism
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After spay or neuter operations, animals are at an increased risk of hypothyroidism. Hypothyroidism refers to the slowing down of thyroid activity and leads to slower metabolism, obesity and hair loss. Obesity in animals carries some of the same risks as in humans, being associated with higher rates of diabetes and cancer.
Incontinence
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Spayed females commonly suffer from urinary incontinence caused by the urethral muscles' failure to contract properly. In some animals the effect is immediate, while in others it may take months or years to become manifest. Intact females rarely suffer from incontinence. Incontinence, which usually requires daily medication, does not seem to affect males.
Apart from the incontinence issue, neutered male cats are less likely to spray urine than their intact counterparts, because the impulse to mark their territory declines with their levels of sex hormones.
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