Weight
Spaying and neutering have long been implicated in weight gain and the studies confirmed there is moderate increase in the risk of obesity for dogs who have been spayed and neutered. However, the studies did not show the age of spaying or neutering to change the risk of obesity. It is also important to note that while spaying and neutering decrease metabolic rate, environmental factors such as lack of exercise and excessive calorie intake play much bigger roles in the obesity epidemic and dogs who have been spayed or neutered will still maintain a healthy weight if fed and exercised appropriately.
Orthopedic Disease
This may be the area with the most clearly defined risks and benefits. It is well documented that spaying and neutering before skeletal maturity is reached (before the growth plates have closed) will delay closure of the growth plates which will result in disproportionately long limbs. This changes the stress and load on the joints which increases the risk of orthopedic diseases such as cranial cruciate rupture (analogous to an ACL tear) and hip dysplasia. This risk is most dramatic in large and giant breed dogs (adult weight over 50 pounds) considering they are already more at-risk for orthopedic disease and their growth plates close at a later age than smaller dogs. Because of this, at the Pet Hospitals we recommend large and giant breed dogs wait to be spayed or neutered until they reach skeletal maturity (generally between 12-15 months of age).
For each breed represented on a separate page in Appendix 1, the numbers of intact and neutered males and females are given. In the tables, the percentage of dogs with each of the diseases and the percentage having at least one of the joint disorders and at least one of the cancers (except MC) was calculated for intact males and intact females as well as those neutered at various age ranges. Statistical analyses compared the occurrences of joint disorders and cancers between each neuter period and intact dogs. If the comparison was significant at either the p <0.05 or p <0.01 level, the data were bolded and the p-value was given. The detailed datasets are available online (Figshare, doi: 10.6084/m9.figshare.7231010). Three breeds for which findings have been previously published (Golden Retriever, Labrador Retriever, German Shepherd Dog) are included to present an overall picture in the same Appendix 1. The data for these three breeds were expanded through 11 years of age, to provide continuity among breeds and diseases.
The study population was 318 intact males, 365 neutered males, 190 intact females, and 374 spayed females for a total of 1,247 cases. In intact males and females, the level of occurrence of one or more joint disorders was 5 percent and 4 percent, respectively. Neutering males at <6 mo. and at 6–11 mo. was associated with risks of 25 percent and 11 percent, respectively (p <0.01). In females, spaying at <6 mo. and at 6–11 mo. was associated with risks of 18 percent and 11 percent (p <0.01, when combined). The occurrence of one or more of the cancers followed in intact males was a high 15 percent and for intact females 5 percent. Neutering males at <6 mo. and at 6–11 mo. was associated with increased risks of cancers to 19 and 16 percent, respectively (p <0.01). Spaying females at <6 mo. and at 6–11 mo., was associated with increases in cancers to 11 and 17 percent, respectively (p <0.05, when combined) and spaying at 1 year and at 2–8 years was associated with increased risks of 14 percent (p <0.01, when combined). The occurrence of MC in intact females was 1 percent and for those spayed at 2–8 years, 4 percent. For females left intact, 4 percent were reported with PYO. No cases of UI were reported in females spayed at any age. The suggested guideline for males, based on the increased risks of joint disorders and cancers, is delaying neutering until beyond a year of age. The suggested guideline for females, based on the increased occurrence of cancers at all spaying ages, is leaving the female intact or spaying at one year and remaining vigilant for the cancers.
The study population was 315 intact males, 152 neutered males, 143 intact females, and 239 spayed females for a total sample of 854 cases. Joint disorders are a major concern in this breed with 8 percent of intact males and 16 percent of intact females having one or more joint disorders. In males, neutering at <6 mo. and at 6-11 mo. resulted in 10 percent and 22 percent occurrences (combined p <0.05). In females, spaying at <6 mo. resulted in a significant 43 percent occurrence (p <0.05), the main joint disorder being CCL. The cancers followed occurred in the intact males and females at 16 and 11 percent, respectively. These relatively high occurrences of cancers in intact males and females were not increased by neutering at any age. Of females left intact or spayed at 2–8 years, 8 and 5 percent were diagnosed with MC, respectively. In intact females, 12 percent were diagnosed with PYO. With regard to UI, 1 percent of intact females had UI, and in females spayed at <6 mo. and 6-11 mo., 4 and 6 percent, respectively had UI. The suggested guideline for males, given the risk of joint disorders for those neutered at 6-11 mo. or earlier, is neutering beyond a year of age. For females, given the increased risk of joint disorders with neutering at <6 mo., the suggested guideline is spaying beyond 6 months.
The study population was 96 intact males, 106 neutered males, 63 intact females, and 118 spayed females for a total sample of 383 cases. In intact males and females, the occurrences of joint disorders were zero and 2 percent, respectively. In neutered males and females, there was no evident increased occurrence of joint disorders. The level of occurrence of one or more cancers in intact males was 6 percent and in intact females, 8 percent. Neutering males and females did not lead to any evident increase in risk of a cancer. There were no cases of MC in females left intact or spayed at any time, and there was a 5 percent occurrence of PYO in the intact females. None of the females was diagnosed with UI. Lacking a noticeable occurrence of increased joint disorders or cancers in neutered males or females, those wishing to neuter should decide on the appropriate age.
19. Perry RJ, Farquharson C, Ahmed SF. The role of sex steroids in controlling pubertal growth. Clin Endocrinol. (2008) 68:4–15. doi: 10.1111/j.1365-2265.2007.02960.x
When Is It Too Late To Neuter A Dog?
In the United States, it is now common to have all dogs and cats not meant for breeding purposes spayed (ovariohysterectomy) or neutered (castration). In fact, 78% of dog-owning households have spayed or neutered their canine companions according to the American Pet Products Association’s 2019-2020 National Pet Owners survey.
This near-routine practice was a result of veterinarians and the animal shelter community working together to reduce the number of unwanted animals that would be euthanized. Currently, Statista estimates that 6.5 million animals enter U.S. animal shelters each year. Of that number, it’s estimated that 1.5 million are euthanized. Although euthanasia has decreased over the last decade or so, there remains a very strong case for routine spay/neuter of pet cats and dogs.
Often, the spay and neuter take place at a very young age for pets, at four to six months. However, studies have shown that this may not be the best age to spay or neuter your dog. The relationship between sex hormones and canine health was not well-considered and understood decades ago when the early spay/neuter campaigns were started. Today, we are discovering that possibly some of those decisions may have affected the health of some dogs.
Research conducted by the University of California – Davis reveals that for some dog breeds, neutering and spaying may be associated with the increased risks of certain health conditions such as joint disorders including hip or elbow dysplasia, cranial cruciate rupture or tear, and some cancers, such as lymphoma, mast cell tumor, hemangiosarcoma, and osteosarcoma. The research conclusions are not surprising. Sex hormones are important in the development of any animal. We know they affect psychological development as well as the musculoskeletal, cardiovascular, and the immune system.
Interestingly though, different breeds and different sized dogs mature at different ages, which means that early spay/neuter may not be bad for all dogs. The wide margin of maturation of dogs varies considerably, as toy breed dogs mature sexually as early as six to nine months of age whereas large and giant breeds may mature as late as 16-18 months of age. The end conclusion is that generally, the larger breeds had possibly more to risk in future health conditions in than small or toy breeds of dogs due to early spaying or neutering since they mature at a later age.
The American Veterinary Medical Association “promotes the professional judgment of the veterinarian in developing an informed, case by case assessment of each individual patient, taking into account all the potential risks and benefits of spay/neuter.”
My opinion on the topic is that the best age to spay or neuter should no longer be the standard “six months of age” response that many veterinarians have used as a guideline over the years, but rather tailored to each individual dog, especially if the dog is a large or giant breed. If you have a purebred dog, you should also speak with your breeder, who may be able to provide valuable insight. Then, a discussion with your veterinarian based on your dog’s breed or breed type, sex, and potential future medical concerns must be had.
An age of six to nine months of age may be appropriate for neutering or spaying a toy breed puppy or small breed puppy but a larger or giant breed may need to wait until they are near or over 12-18 months of age. It is also important to understand that often, the earlier these procedures are done, the easier the surgeries usually are for the veterinarian and recovery for the patient. The one rule I recommend is to not knowingly spay a female dog while they are going through their heat cycle as that may exacerbate excessive bleeding.
Spaying and neutering pets remains an important part of the effort to reduce the number of unwanted animals and unnecessary euthanasia in this country. When considering whether to spay or neuter your dog, with today’s information about the possible effects of age at the time of surgery on their future health, it is ideal to have a detailed discussion with your veterinarian to determine what is best for your dog.
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