Most of you who are interested enough to read this are familiar with a few studies done at UC Davis about disease incidence and spay/neuter status. These were retrospective studies which are basically the lowest kind of scientific evidence. There are several additional flaws or factors in these studies we need to point out before we take the potential findings into consideration.
1. The studies were done on breeds that are predisposed to the diseases in question. If all breeds were included the results would be different. If only chihuahuas were studied the results would be vastly different. Because breed and genetic predispositions are so different we can't necessarily extrapolate this info to all dogs.
2. Dogs over 8 years old were excluded. Dogs that got cancer or orthopedic disease beyond age 8 were considered to have gotten it because those are diseases of older dogs. I don't know why this decision was made.
3. All the dogs in the study were seen at a specialty referral hospital. This is a pretty limited population, which does not include all the types of dogs in general practice who have the same diseases but were not included in the study.
4. Statistics are tricky. While a result may indicate the incidence of a disease doubles, if it's an uncommon disease to begin with you may be talking about 2 in 10,000 dogs instead of 1. While this is very important if it's your dog, it's not necessarily statistically relevant.
5. There is no way to account for variables such as weight, lifestyle, diet, and so on and so forth forever. This is also the problem with any future studies being done. There is no practical way to have any wide scale study that controls all these variables.
6. Correlation does not equal causation. Take the grain free food and heart disease issue for example. We don't think it's actually the lack of grains that are the issue but it's still associated with the cardiomyopathy.
7. Results did not universally recommend one thing or the other. Individual disease incidence varied depending on the age of neuter and sex of the dog. Essentially the same dog could be more predisposed to one thing and less to another so generalizations can be hard.
So, what did we learn form this study? Basically that more research is needed, particularly in some breeds of dogs.
Now, to keep things relatively simple we are doing to discuss the pros and cons of "traditional" spay/neuter age considered to be about 6 months vs "delayed" spay/neuter which we will call after skeletal maturity. I'm not including any info on osteosarcoma, hemangiosarcoma, lymphoma, mast cell tumors or immune mediated diseases as I don't think there is near enough research and these diseases all have too many of their own genetic variables.
Benefits specific to early spay:
- Convenience/no heat cycles
- Population control
- Virtually no chance of mammary cancer
- Ease of surgery/recovery time
Benefits of spay at maturity:
- Significantly deceased incidence of mammary cancer (based on only having one heat cycle, protective benefits of spay decrease with each cycle and a certain point spay no longer has a protective effect)
- Eliminates risk of pyometra
- Eliminates risk of ovarian and uterine cancer or disease
- Potentially reduced risk of orthopedic disease (compared to earlier spay), mainly in larger breed dogs
A word about urinary incontinence. Spayed females are more likely to have incontinence than intact, however age at spay does not consistently seem to matter as much as the adult weight of the dog. Larger breed dogs tend to have a bigger issue. Actual incidence of incontinence overall seem unknown as studies show widely variable results. Personally, I don't diagnose true incontinence very often, but that's not scientific!
Benefits specific to early neuter:
- Convenience/less marking/male dog behavior
- Population control
- Ease of surgery/recovery time
Benefits of neuter at maturity:
- Reduced or eliminated risk of prostatic hypertrophy, prostatic infections and abscesses (interestingly, prostate cancer is actually more common in neutered dogs-but is rare)
- Eliminates risk of testicular cancer or other rare diseases such as torsion
- Reduced risk of perineal hernia and perianal gland tumors
- Potentially reduced risk of orthopedic diseases (compared to earlier neuter), mainly in larger breed dogs
This is certainly not an all inclusive report of all diseases and risks but I think it covers the basics. There is also a lot of variability in any of these topics such as-how often are mammary cancers malignant, or is the dog even clinical for the hip dysplasia, and on and on in a never ending cycle of pros and cons. The important thing is to prioritize what is important to you as the pet owner and be comfortable with that decision. Remember, there is no "control" for your dog. This means you can't know that something would or wouldn't have happened if you had made a different decisions. Would your dog have still ruptured his cruciate if you waited until 18 months to neuter him instead of 6? Maybe yes. Maybe no. Would you have spared your dog of mammary cancer if you spayed her a little sooner? Maybe, maybe not. There is a lot of this that just isn't black and white.
However, generally speaking dogs are living longer, healthier lives than ever before thanks to advances in veterinary medicine, good preventative care and maintaining healthy weights. So don't overthink it too much! And if you don't like my summary, you can find the answers you prefer elsewhere on the internet.
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