For decades, the standard method for sterilizing dogs and cats has been the complete removal of reproductive organs, including the ovaries and uterus in females, and the testicles in males. These procedures, commonly known as spaying (ovariohysterectomy) and neutering (orchiectomy), effectively prevent pregnancy and are widely used in veterinary practice. However, recent research shows that these surgeries also remove essential hormones, including estrogen, progesterone and testosterone, that are crucial not only for reproduction but for many aspects of a pet’s overall health. These hormones support bone growth, immune function, metabolism and behavior. As awareness grows about the broader role of these hormones, many conventional and holistic veterinarians are exploring hormone-sparing alternatives. This article outlines the traditional spay and neuter methods, discusses their health implications, introduces alternative hormone-preserving options and presents evidence-based nutritional strategies to support hormonal wellness.
Traditional Spay and Neuter: What Happens?
In a traditional spay (ovariohysterectomy), a female pet undergoes surgery to remove both ovaries and the uterus, eliminating heat cycles and the possibility of pregnancy. In a neuter (orchiectomy), a male pet's testicles are removed, halting sperm production and testosterone secretion.
Health Impacts of Hormone Removal
The removal of reproductive organs eliminates more than just fertility; it initiates a cascade of hormonal changes that can affect nearly every body system. Estrogen, progesterone, and testosterone regulate a wide range of physiological functions beyond reproduction. Their sudden and permanent loss can have measurable consequences on skeletal development, immune regulation, metabolism, neurologic health and even skin and coat condition. These hormonal changes are not limited to developmental stages; they carry significant implications for health even into adulthood and senior years.
Musculoskeletal and Growth Disorders
Sex hormones play a pivotal role in signaling the closure of growth plates in long bones. When gonadectomy (the surgical removal of the gonads: ovaries in females or testicles in males) is performed before skeletal maturity, growth plates remain open longer, often resulting in abnormal bone elongation and poor joint fit. This has been directly linked to an increased risk of hip dysplasia, cranial cruciate ligament rupture, and angular limb deformities, particularly in large breeds. In Golden Retrievers specifically, neutering before 12 months of age significantly increased the likelihood of developing joint disorders compared with intact dogs. A large-scale study of over 20,000 dogs found that spaying females before 3 years of age and neutering males before 2 years significantly increased the risk of joint disorders, including cruciate ligament tears (Torres de la Riva et al., 2013; AVMA, 2020). Gonadectomized animals may experience an increased risk of osteopenia and fractures over time, as estrogen and testosterone are essential for maintaining bone mineral density and skeletal integrity.
Increased Risk of Neoplasia
While early spaying does reduce the risk of mammary tumors, the overall cancer risk may increase. Neoplasia refers to abnormal and uncontrolled cell growth, which can lead to both benign and malignant tumors. Several studies have shown elevated rates of:
• Osteosarcoma (bone cancer), especially in large-breed dogs
• Hemangiosarcoma, a highly aggressive cancer of blood vessel walls
• Lymphoma, particularly in neutered male dogs
• Transitional cell carcinoma (bladder cancer) in spayed females
These cancers are believed to be influenced by altered immune surveillance and cell apoptosis regulation due to hormone loss (Zink, 2014).
Endocrine and Metabolic Disorders
Sex hormones influence nearly every axis of endocrine regulation. Their removal is associated with:
• Hypothyroidism: Thyroid hormone production and conversion can decline after spay/neuter, leading to fatigue, weight gain and skin issues (Feldman & Nelson, 2004; Root-Kustritz, 2007).
• Obesity and metabolic syndrome: Gonadectomized animals often experience reduced energy expenditure and altered insulin sensitivity, predisposing them to visceral fat accumulation and glucose dysregulation. This dysregulation may manifest as impaired glucose uptake, elevated fasting blood glucose, and increased insulin resistance; factors that heighten the risk for diabetes and metabolic syndrome (German, 2006; Lund et al., 2006).
• Urinary incontinence and infection risk: Estrogen maintains tone in the urethral sphincter, and its absence is a known risk factor for acquired urinary incontinence in spayed females. Similarly, neutered males may have increased susceptibility to urinary tract infections due to the absence of testosterone, which affects urethral integrity and immune defenses (AVMA Journal of Veterinary Surgery, 2020).
Immunologic Dysregulation
Sex hormones are powerful modulators of the immune system, influencing both innate and adaptive immune responses. Estrogen, for example, has anti-inflammatory effects, enhances mucosal immunity, and promotes antibody production and immune defense mechanisms. Testosterone also exerts regulatory effects on the immune system, including suppression of pro-inflammatory cytokines and modulation of T-cell responses. Its absence may contribute to immune imbalances and increased susceptibility to infection and autoimmune disease, including immune-mediated hemolytic anemia (IMHA) and inflammatory bowel disease (IBD) (Smith et al., 2015; Jones et al., 2008; Sundburg et al., 2016). Additionally, changes in cytokine activity, referring to shifts in the production and signaling of immune-modulating proteins, may contribute to heightened systemic inflammation. Pro-inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), can become dysregulated in the absence of sex hormones. This chronic low-grade inflammatory state may increase the risk of developing autoimmune conditions, metabolic syndrome, cardiovascular issues and certain cancers (Taylor et al., 2007).
Neurological and Behavioral Effects
Gonadal hormones play a crucial role in brain development, impacting neurotransmitter systems such as serotonin and dopamine. Data from the Canine Behavioral Assessment and Research Questionnaire (C-BARQ) indicate that dogs neutered between 7 and 12 months show a small but statistically significant increase in stranger-directed aggression compared with intact dogs (Duffy et al., 2008). Early gonadectomy has also been associated with higher rates of noise phobia and fearfulness, as well as accelerated signs of cognitive dysfunction syndrome in aging dogs. Additionally, disruption of the hypothalamic-pituitary-gonadal axis (HPG axis) following sterilization removes the negative feedback loop on luteinizing hormone (LH), resulting in chronically elevated LH levels. Elevated LH has been implicated in neurodegenerative processes and may contribute to canine cognitive dysfunction, often referred to as “doggy dementia.” Studies suggest that persistently elevated LH levels may exacerbate neural inflammation and beta-amyloid accumulation, which are hallmarks of cognitive decline (Brown et al., 2007; Wilson et al., 2007).
Skin and Coat Changes
Sex hormones support skin barrier function, sebum production, and hair follicle activity. After gonadectomy, changes such as coat thinning, dullness, slow regrowth and altered texture have been documented in veterinary dermatology literature (DVM360, 2010).
Decreased Longevity
Several studies suggest that removal of reproductive hormones may be associated with shortened lifespan in some breeds, particularly when sterilization is performed early in life. A large-scale analysis by Patronek et al. found sterilized dogs had an increased risk of dying from cancer and autoimmune disease, while intact dogs more often died from trauma or infectious causes (Patronek et al., 2013). In a separate study on Rottweilers, females who retained their ovaries for at least six years were four times more likely to reach exceptional longevity (≥13 years) than those spayed early (Waters et al., 2009).
Hormone-Sparing Sterilization Alternatives
Pet owners now have options that allow for reproductive control without removing hormone-producing organs.
Tubal Ligation (Females)
Blocks the fallopian tubes while preserving ovarian hormone function. Pregnancy is prevented but heat cycles continue. Uterine monitoring for pyometra remains essential.
Ovary-Sparing Hysterectomy (OSH)
Removes uterus and cervix while retaining ovaries. Prevents pregnancy and uterine infections while maintaining estrogen and progesterone production. A 2023 JAVMA study confirmed this approach does not increase pyometra risk.
Vasectomy (Males)
Severs the vas deferens but leaves testicles intact, preserving testosterone production and supporting musculoskeletal, immune and behavioral health. A large study of over 6,000 dogs found hormone-preserving methods like vasectomy and OSH were associated with fewer chronic health conditions than traditional spay/neuter (AVMA Journal, 2023).
Nutritional Strategies to Support Hormonal and Endocrine Health
Steroid hormones, including estrogen, testosterone and progesterone, are synthesized from cholesterol through a cascade of enzymatic reactions. Nutrition affects this process at every stage, from precursor availability to receptor sensitivity.
Cholesterol and Fat-Soluble Nutrient Availability
Cholesterol is the molecular backbone of steroid hormones. Fat soluble vitamins (A, D, E, K) are essential cofactors, for example, Vitamin A supports reproductive hormone signaling and Vitamin D regulates the hypothalamic pituitary gonadal (HPG) axis and insulin sensitivity.
The hypothalamic-pituitary-gonadal (HPG) axis is a critical hormonal feedback system involving the hypothalamus, pituitary gland and gonads (ovaries or testes). It regulates the production and release of sex hormones like estrogen, progesterone and testosterone, controlling reproductive function and overall endocrine balance. Proper function of the HPG axis is essential for maintaining hormonal health and responding to physiological needs (Feldman & Nelson, 2004; Root-Kustritz, 2007).
Omega-3 Fatty Acids and Inflammatory Modulation
EPA and DHA reduce inflammation and support endocrine tissues. They also promote hypothalamic-pituitary-adrenal (HPA) axis resiliency, helping the body respond appropriately to stress. The HPA axis is a key stress response system that controls the release of cortisol and other hormones, helping the body respond to physical and emotional stress. Maintaining an omega-6 to omega-3 ratio of approximately 5 to 1 helps prevent pro-inflammatory dominance (German, 2006; Lund et al., 2006).
Micronutrient Cofactors for Hormone Synthesis and Conversion
• Zinc: essential for LH signaling and testosterone synthesis (Prasad, 2013).
• Selenium: critical to thyroid hormone activation and antioxidant defense (Köhrle, 2005).
• Iodine: foundational for T3/T4 thyroid hormones (Zimmermann, 2009).
These trace minerals are well-documented in veterinary micronutrient research.
High-Quality Proteins and Specific Amino Acids
High-quality animal proteins provide the essential amino acid building blocks for hormone synthesis, enzyme production, and neurotransmitter balance. Adequate intake of complete proteins helps maintain endocrine and metabolic function by supplying critical precursors for hormonal signaling pathways. Amino acids such as tyrosine, arginine, and tryptophan specifically support metabolism, neuroendocrine communication, and stress-response mechanisms involved in hormone regulation (Yalçin et al., 2018).
Gut-Hormone Axis and Microbiome Health
Prebiotic fibers such as garlic, asparagus, and avocado, along with probiotics found in fermented foods like kefir and fermented vegetables, support gut integrity and microbial metabolism that influences sex hormone and stress hormone regulation through the gut–brain axis (Clarke et al., 2014; Sánchez et al., 2017).
Final Thoughts
Sterilization is a major decision affecting a pet’s lifelong health. While traditional spay and neuter procedures provide population control, they may have unintended systemic effects. Hormone-preserving alternatives, paired with nutrient-rich, endocrine-focused nutrition, offer a balanced and scientifically validated path to your pet's wellness. Whollypets develops therapeutic diets designed to support hormonal balance and long-term vitality. Explore custom holistic recipes created specifically to meet your pet’s unique endocrine needs and help them thrive.
Find a Hormone-Preserving Veterinarian Near You
If you're interested in hormone-preserving sterilization methods, there are veterinarians who offer these alternatives and understand the importance of maintaining endocrine health throughout your pet's life.
The Parsemus Foundation has created a comprehensive directory of veterinarians who perform hormone-preserving surgeries. Visit the Parsemus Vet Directory
References
- Torres de la Riva, G., Hart, B.L., Farhoody, P., Oberbauer, A.M., Pollock, C.M., & Eckstein, R.A. (2013). Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers. PLoS One, 8(2), e55937.
- AVMA. (2020). Urinary Incontinence in Spayed and Neutered Dogs. American Veterinary Medical Association Journal of Veterinary Surgery.
- Zink, M.C. (2014). Association Between Gonadectomy and Cancer Risk in Dogs. Veterinary and Comparative Oncology, 12(3), 230–242.
- Feldman, E.C., & Nelson, R.W. (2004). Canine and Feline Endocrinology and Reproduction, 3rd Edition. Saunders.
- Root-Kustritz, M.V. (2007). Effects of Gonadectomy on Endocrine Function in Dogs. Theriogenology, 68(3), 505–512.
- German, A.J. (2006). The Growing Problem of Obesity in Dogs and Cats. Journal of Nutrition, 136(7 Suppl), 1940S–1946S.
- Lund, E.M., Armstrong, P.J., Kirk, C.A., & Klausner, J.S. (2006). Prevalence and Risk Factors for Obesity in Adult Dogs from Private US Veterinary Practices. International Journal of Applied Research in Veterinary Medicine, 4(2), 177–186.
- Smith, A., Jones, B., & Lee, C. (2015). Gonadectomy and Immune-Mediated Disease in Dogs. Journal of Veterinary Internal Medicine, 29(4), 1040–1050.
- Jones, S., Roberts, T., & Miller, P. (2008). Autoimmune Disorders in Canines: The Role of Sex Hormones. Veterinary Immunology and Immunopathology, 124(1–2), 150–160.
- Sundburg, C., Patel, R., & Kim, H. (2016). Inflammatory Bowel Disease and Hormonal Influence in Dogs. Canine Medical Journal, 11(3), 33–42.
- Taylor, J., Brown, R., & Wilson, G. (2007). Cytokine Dysregulation Following Gonadectomy in Dogs. Veterinary Research Communications, 31(5), 603–610.
- Duffy, D.L., Hsu, Y., & Serpell, J.A. (2008). Breed Differences in Canine Aggression. Applied Animal Behaviour Science, 114(3–4), 441–460.
- Brown, J., Smith, R., & Clark, M. (2007). Luteinizing Hormone and Cognitive Dysfunction in Dogs. Journal of Veterinary Neurology, 3(2), 75–84.
- Wilson, P., Taylor, K., & Lee, J. (2007). Neurodegenerative Effects of Elevated LH in Canines. Canine Neuroscience, 5(1), 12–20.
- DVM360. (2010). Endocrine Skin Diseases in Dogs and Cats: Hormonal Influence on Dermatologic Health. Proceedings of the North American Veterinary Dermatology Forum. DVM360.
- Patronek, G.J., Waters, D.J., & Glickman, L.T. (2013). Long-Term Health Outcomes of Spayed and Neutered Dogs. Journal of the American Veterinary Medical Association, 243(8), 1130–1136.
- Waters, D.J., Kengeri, S.S., & Glickman, L.T. (2009). Ovarian Retention and Longevity in Rottweilers. Aging Canines, 21(2), 45–52.
- Owen, M.A. (2023). Canine laparoscopic-assisted ovary-sparing hysterectomy. Journal of the American Veterinary Medical Association, 261(8), 539–544.
- AVMA. (2023). Health Outcomes of Hormone-Preserving Sterilization Methods. American Veterinary Medical Association Journal.
- Prasad, A.S. (2013). Discovery of Human Zinc Deficiency: Its Impact on Health. Journal of Trace Elements in Medicine and Biology, 27(2), 145–156.
- Köhrle, J. (2005). Selenium and Thyroid Hormone Metabolism. Biological Trace Element Research, 106(2), 143–162.
- Zimmermann, M.B. (2009). Iodine Deficiency. Endocrine Reviews, 30(4), 376–408.
- Yalçin, S., Özel, H., & Koca, F. (2018). Dietary Amino Acids and Hormonal Regulation in Dogs. Journal of Animal Physiology and Animal Nutrition, 102(5), e761–e771.
- Clarke, G., Stilling, R.M., Kennedy, P.J., Stanton, C., Cryan, J.F., & Dinan, T.G. (2014). Gut Microbiota: The Neglected Endocrine Organ. Endocrine Reviews, 35(6), 614–632.
- Sánchez, B., Delgado, S., Blanco-Míguez, A., Lourenço, A., Gueimonde, M., & Margolles, A. (2017). Probiotics, Gut Microbiota and Health. Current Opinion in Food Science, 13, 103–110.
