Effects of Sterilization (Spaying and Neutering)

Contrary to popular belief, sterilization surgeries – spaying and neutering, will not resolve the dog’s behavioral issues. Any correlation that a novice owner might notice is false – the dog “settled down” not because he was neutered, but because the surgery was done when the puppy is still developing – and so of course, as the dog matures, he will become calmer. Growing up is what made the dog calmer, not surgically removing his testicles. American Bulldogs generally continue to mature, both physically and mentally, until 3 years of age.


There is a myth that neutering a male dog will prevent prostatic carcinoma (PC) – cancer of the prostate gland. This is not true. Castration at any age shows no sparing effect on the risk of development of prostate cancer in the dog. (J Obradovich et al. 1987)


Sterilization should only be considered when there is a medical necessity to alleviate an existing, usually potentially fatal problem, as risks far outweigh any perceived benefits. Some examples of medical necessities for females are pyometra – a bacterial infection of the uterus which in some instances is not curable and could be deadly, and for males – cancers of the genital region.


Before you read the jaw-dropping list below of the permanent consequences of spaying and neutering on the dog’s health, it is important to understand the underlying effect the sterilization has on the dog to help explain and comprehend the severe consequences:


Sex organs serve a vital function in an organism. These include but are not limited to testosterone, estrogen, and androgens in both sexes. The variety of hormones are produced in very specific amount in an intact dog, and these hormones affect everything in the organism.


1) An American Bulldog puppy is born at around 1 lb of weight, and can develop to be over 100 lbs by the age of 1 year old. Bone growth is directly controlled by the hormones produced by the dog’s sex organs. Some of the largest bones in the body, such as the femur, only stop growing at around 2.5 – 3 years of age. The bone’s epiphyseal growth plates “close,” and this process is again hormonal. The process is regulated by both estrogen and testosterone. If a dog is missing the sex organs, then the organism is not capable of sending the hormonal signal to the bones to stop growing, and as a result such bones continue to grow past the genetically predetermined timing. This is why some bones of sterilized dogs are bigger and longer. However, the surrounding joints, ligaments, cartilages, and muscles remain their genetic size. The anatomy of the dog is no longer congruent, which causes the biomechanics of the dog to be improper as well, causing unnatural stresses on various joints around the body. That is why sterilized dogs are much more susceptible to catastrophic anatomical problems, such as CCL (knee) ligament ruptures and hip dysplasia.


According to Chris Zink, DVM: (Please note that timing of bone growth ending varies based on breed and size, and in the case of American Bulldogs the figures below are around 2.5-3 years of age)

“For example, if the femur has achieved its genetically determined normal length at 8 months when a dog gets spayed or neutered, but the tibia, which normally stops growing at 12 to 14 months of age continues to grow, then an abnormal angle may develop at the stifle. In addition, with the extra growth, the lower leg below the stifle likely becomes heavier (because it is longer), and may cause increased stresses on the cranial cruciate ligament.”


2) Proper hormone function, which is drastically disrupted by the removal of sex organs, also plays a key role in the overall immune system. Hormones even affect organ function, and essentially every aspect of your dog’s organism. Testosterone for example affects the building of muscle, the rebuilding of tissue post injury, the control of temperature and regulatory processes, and modulates rate of growth.


Please note that below is an incomplete list of all the conclusive research that has been done on the effects of sterilization.


SUMMARY: “Spaying and neutering is associated with an increased risk of several long-term health problems including obesity, urinary incontinence, bladder stones, hypothyroidism, diabetes mellitus, hip dysplasia, cruciate ligament rupture, behavioral changes (including owner-directed aggression and fear), cognition problems, as well as several forms of cancer (including leukemia, prostate cancer, bone cancer, skin cancer, splenic cancer, and bladder cancer).” (Kutzler, Michelle A. 2020)


Prevalence of ACL (knee ligament) rupture in spayed females and neutered males was 2.1-fold higher than in sexually intact animals. (Slauterbeck, JR et al.)


A study in the Journal of Veterinary Internal Medicine, compiled over 13 years found that “… neutering dogs appeared to increase the risk of cardiac tumour in both sexes”. The results showed that spayed females were five times more likely to suffer tumors of the heart than intact females (Ware and Hopper 1999), one of the three most common cancers in dogs today.


In another study spanning 14 years of research and involving 3062 purebred dogs with osteosarcoma compared to 3959 purebred dogs without osteosarcoma, it was concluded that sterilisation increased the risk for bone cancer in large breed purebreds twofold (Ru et al. 1998).


A study of 759 golden retrievers found that there were no cases of cranial cruciate ligament tear diagnosed in intact males or females, but in neutered males and females the occurrences were 5 percent and 8 percent. (Torres de la Riva et al. 2013). In this study, 10 percent of neutered males were diagnosed with hip dysplasia, exactly double the occurrence in intact males. Further, almost 10 percent of neutered males were diagnosed with lymphosarcoma, a potentially deadly cancer, 3 times more than intact males.


Neutering Golden Retriever females at any time through 8 years of age increased the rate of at least one of the cancers by 3–4 times. List of cancers that were tracked in the study: lymphosarcoma, hemangiosarcoma, mast cell tumor, and mammary cancer. (Hart BL, et al. 2014)


A study of nearly 500 Rottweiler females found that neutering before four years of age reduces life expectancy by 30%. Females that kept their ovaries the longest were nine times more likely to achieve exceptional longevity (13+ years).” (Waters, David J et al. 2009)


Urinary incontinence after spaying prior to their first heat occurred in 12.5% of bitches over 44 lbs, and roughly 20% for females spayed after their first heat suffered from this permanent side effect of the surgery. (Stöcklin-Gautschi NM et al. 2001) (Note: Please understand that urinary incontinece incidence is essentially zero in unaltered dogs. Urinary incontinence is when the dog is unable to control her bladder – so the dog constantly urinates anywhere and everywhere. Really think about what that means to the dog’s and your life.)


Sterilized dogs had a significantly higher risk of atopic dermatitis, autoimmune hemolytic anemia, hypoadrenocorticism, hypothyroidism, immune-related thrombocytopenia, and inflammatory bowel disease than intact dogs. (Sundburg, C.R. et al. 2014)