Thanks for that.
Really interesting and I will talk to some vet friends about their views.
The problem with a lot of the studies -- and articles assessing them! -- is exactly this risk of bias or sample size.
That alone would make me want to know more about the people who wrote this assessment. Makes the issue even more complicated than it already is, on health perspectives.
To my mind the one major review of test results that I see posted widely, looking at a huge range of diseases, comes across as highly biased as it does not list the likelihood of dogs ever getting some of the 'increased risk' diseases', set against some of the more common risk diseases. A lot of the 'increased risk' factors they site just are miniscule risks or very small sample studies.
And important to note that none of these 'health' arguments consider what I still strongly assert is the biggest issue around neutering -- the risk of unwanted pregnancies and therefore, deaths of unwanted puppies; the risk of death and complications -- significant in itself -- to a pregnant bitch simply in being pregnant; the risk of behavioural issues stemming directly from not neutering a younger dog resulting in that dog 1) getting out and either being killed, or lost; 2) being attacked/attacking other dogs and seriously harmed; 3) being dumped or sent to the pound by people who cannot manage or don't know how to manage normal but unwanted intact-dog behaviours. The latter is a significant reason for dogs ending up in the pounds/ending up spending its life outside in a garden.
The article I linked to at the top is interesting to me as it was done at UC Davis, which is very reputable
; the sample size is fairly large; the results look at some gender indications.
The results do suggest a greater risk of cancer in late-spay (after a year old) females which may be an mportant factor for some people regardless of whether mammary tumour risk are slightly decreased or not decreased. Interestingly the study also suggests slightly higher risks for neutered dogs compared to unneutered dogs overall, but again -- so many of the serious death risks to dogs -- led by either escaping, or ending up in the pound for behaviour issues -- are directly connected to the dogs being intact.I would say the risk of the average dog dying or being lost forever for these reasons is significantly higher than it ever getting a disease that it may be at slightly elevated risk for due to neutering. I think it would be hard to find anyone in rescue or a professional trainer who would not agree with that.
Personally I do not know of any cases of mammary tumours in spayed females, amongst all my rescue contacts or god owning friends. But in rescue we typically see them -- often a LOT of them in a single dog
-- in unspayed older females. Often there's little that can be done in these cases.
My own preference is to neuter around age one these days but I would never rehome an unneutered rescue dog, regardless of age (well not entirely true -- very old intact dogs stay that way!)