Diseases Overview

Once your dog is spayed or neutered, for the rest of your dog’s life, their organ systems will be struggling to create some type of hormonal balance. Failure to maintain hormonal balance can lead to catastrophic outcomes.

Clearly, the concept of spay/neuter to curb overpopulation and perhaps make dogs more manageable did not take into account the possible unintended consequences of wholesale removal of sex hormones as a means of rendering dogs sterile.

Current scientific study has established that sex hormones are responsible for much more than reproduction in dogs (and humans). Sex hormones affect canine growth and development, behavior, immune system competency, and a dog’s susceptibility to major diseases including cancer, diabetes and other metabolic or endocrine-related disease.

This section of our website will explore the increased incidence of cancer and emerging chronic diseases spay/neuter causes – only some of which the veterinary community has acknowledged. We experienced many of these clinical disorders with our own dog Billy. All of our conclusions as to how and why these diseases are occurring are supported by research on both canines and humans.


Most hormones are produced by a group of glands known collectively as the endocrine system. Even though these glands are located in various parts of the body, they are considered one system because of their similar functions and relationship to each other.

Your hormones should exist in harmony with each other. When levels of each hormone are in the right proportions, body systems are stable. The body must constantly fine-tune hormone release to keep levels within proper limits. This balance is accomplished through an intricate series of positive and negative feedback mechanisms. According to the Endocrine Society’s latest Scientific Statement on the subject of endocrine disruption, when balance is lost, hormone deficiencies and excesses can cause chronic symptoms and disorders, and raise risks for disease.

“…levels of any hormone must be within a physiologically relevant range to be most effective. Excursions outside of that range to superphysiological (elevated) or subphysiological (depressed) levels for any extended period nearly always result in dysfunction or disease.” 176

HAHD_StoolA critical portion of the endocrine/hormone system can be envisioned as a three-legged stool wherein the adrenal hormones, thyroid hormones and sex hormones balance one another to maintain stability of the endocrine system. Removal of most or all of the sex hormones leg, as happens with spay/neuter, leaves the stool/endocrine system unstable and dangerous.

The adrenal glands, located at the top of each kidney, provide the all important function of producing hormones that help the body control blood sugar, burn protein and fat, react to stressors like a major illness or injury, and regulate blood pressure. After spay/neuter, the adrenal glands must take on the additional burden of producing sex hormones to compensate for the loss of the reproductive organs. Consequently, spay/neuter’s effect upon the dog’s developing endocrine system as a whole is huge, because the gland most affected (the adrenal gland) has so many responsibilities for processes essential to life itself. The younger the dog at the time of spay or neuter, the greater the detrimental effect upon growth, metabolism, immunocompetence and behavior as well as personality development.85

The compromise in immune function created by spay/neuter predisposes dogs to develop cancer as well as other immune-mediated diseases, the most recognizable being allergies, inflammatory bowel disease, and hypothyroidism.26,107,173,183

Over a prolonged period of time, disruption of the endocrine system can create a sustained/chronic stress-related hypercortisolism (excessive cortisol produced by the adrenal glands) which promotes the development of various pathologic conditions, including metabolic syndrome (fat around waist, insulin resistance which can lead to type 2 diabetes, Cushings, decreased bone and muscle mass, diminished sex steroid production, hypothyroidism, hyperestrinism, and reduced levels of growth hormone) as well as cardiovascular conditions.188 These diseases are discussed in detail in our Hormones and the Endocrine System page.

Canine Cushings Disease

For those dogs with orthopedic diseases due to the developmental effects of early spay/neuter, the physical stress of the reparative surgeries and the ongoing pain caused by orthopedic issues that cannot be remedied (e.g. elbow dysplasia) provide evidence as to how the endocrine response to stress in these dogs can be overtaxed and ultimately irreparably damaged. Billy was one of those dogs whose endocrine system could not recover from neutering and the subsequent orthopedic surgeries and treatments. He would go on to develop four chronic diseases associated with a material disruption of the endocrine mediated stress response – hypothyroidism, Atypical Cushings, hyperestrinism and diabetes.