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Conventional wisdom says that altered pets are less likely to soil in the house, to roam and to fight. They won't get testicular, uterine or ovarian cancer or infections, and they'll have a greatly reduced chance of getting mammary cancer. It sounds so great it almost makes you want to rush right out and get spayed or neutered yourself.
Some of those things are true. You can't get cancer or an infection in an organ that you no longer possess, so it's accurate to say that your dog or cat won't get ovarian, uterine or testicular cancer or infections. And there is an increased incidence of mammary cancer in unspayed female dogs and a pretty high rate of uterine infection as well.
But there are also notable health risks associated with having your dogs and cats spayed or neutered.
These include an increased incidence of some cancers, including osteosarcoma, a painful and usually fatal bone cancer, in neutered male dogs.
Neutered males also have a greater chance of getting prostate cancer and transitional cell carcinoma of the bladder.
Spayed females have a greater incidence of urinary incontinence. They may also have a higher risk of bladder infections.
Meanwhile, spayed female and neutered male dogs have a significantly greater incidence of anterior cruciate ligament injuries than intact dogs.
Recent research by Purdue University suggests that female dogs (and, interestingly, female humans) live longer if they keep their ovaries.
And yes, no matter what you've been told, study after study has shown that spayed and neutered dogs and cats weigh more when fed the same amount of calories as intact animals. The surgery won't "make" them fat, but by changing how their metabolism functions, the amount of food they can eat without gaining weight is reduced.
For most dogs and cats that's actually no big deal -- just feed them a little less, exercise them a little more, and they'll be fine. But how do you do that when you're having it beaten into your brain that spaying and neutering does not, cannot, will not make your dog or cat fat or have any other adverse effects?