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. 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. When balance is lost, hormone deficiencies and excesses can cause chronic symptoms and disorders, and raise risks for disease. The endocrine/hormone system can be envisioned as a three-legged stool which, by its very nature, requires a delicate balance be maintained by its support structure. Removal of most or all of one of the legs as happens with spay/neuter, leaves the stool/endocrine system unstable and dangerous.
Hormones are extremely potent substances. It takes only a tiny amount to initiate an action. Hormones are not stored, but produced as needed and secreted into the bloodstream by the glands. From there, they travel to all parts of the body. But only the cells sensitive to that hormone – called the target tissue – will respond to the chemical signal the hormone carries. Traveling through the blood, hormones enter cells through “receptor” sites, much as a key unlocks a door. Once inside, they get to work, flipping the switches that govern growth, development, and mental and physical functions throughout life. 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.
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. It is the intersection of the stress-related duties of the adrenal glands and the new requirement to produce sex hormones that define spay/neuter as the stressor that has a detrimental effect upon the developing “stress response system“. 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
Specifically, the part of the endocrine system most affected by spay/neuter is the Hypothalmic-Pituitary-Adrenal (HPA) axis. The HPA axis, in conjunction with elements of the Central Nervous System (CNS), is central to our body’s ability to respond or adapt to physical and psychological stress. HPA axis integrity and precise regulation of its function are essential characteristics of the successful adaptive response to any stressor.85 So, as the spayed or neutered dog ages and/or is subjected to physical or emotional stress (surgery, injury, rehoming) the adrenal glands are overburdened and unable to maintain HPA axis hormone balance. Hormonal imbalance means signals do not reach the right place at the right time. Sometimes cell functions shut down completely. In other cases, cells are over stimulated. A disruption in the balance of hormones produced by one gland or set of glands can cause other gland systems to malfunction.
Specific areas of the CNS have critical, distinct roles along with the HPA axis in orchestrating the stress response. These would include the hypothalamus and the brainstem. Dogs with a crippled “stress response system” may develop behavioral problems that can lead to them being left at a shelter or euthanized due to their “aggressive” tendencies. Well established interactions exist between the “stress response system” and Central Nervous System (CNS) centers essential for survival such as the thermoregulatory and appetite-satiety centers. Failure of the “stress response system” can result in an elevated core temperature and anorexia or overeating leading to obesity. Over a prolonged period of time, disruption of the “stress response 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. Hyperactivation of the “stress response system” has also been implicated in the development of allergies and autoimmune disease, as well as increased susceptibility to infections, tumors and metastasis of said tumors should they be malignant.85 These diseases are discussed in detail in our Hormones and the Endocrine System page.
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) are “insult added to injury”. 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 of the endocrine system – hypothyroidism, Atypical Cushings, hyperestrinism and diabetes.