http://naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf[/color]
On balance, it appears that no compelling case can be made for neutering most male dogs, especially immature male dogs, in order to prevent future health problems. The number of health problems associated with neutering may exceed the associated health benefits in most cases.
On the positive side, neutering male dogs
eliminates the small risk (probably <1%) of dying from testicular cancer
reduces the risk of non-cancerous prostate disorders
reduces the risk of perianal fistulas
may possibly reduce the risk of diabetes (data inconclusive)
On the negative side, neutering male dogs
if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common cancer in medium/large and larger breeds with a poor prognosis.
increases the risk of cardiac hemangiosarcoma by a factor of 1.6
triples the risk of hypothyroidism
increases the risk of progressive geriatric cognitive impairment
triples the risk of obesity, a common health problem in dogs with many associated health problems
quadruples the small risk (<0.6%) of prostate cancer
doubles the small risk (<1%) of urinary tract cancers
increases the risk of orthopedic disorders
increases the risk of adverse reactions to vaccinations
For female dogs, the situation is more complex. The number of health benefits associated with spaying may exceed the associated health problems in some (not all) cases. On balance, whether spaying improves the odds of overall good health or degrades them probably depends on the age of the female dog and the
relative risk of various diseases in the different breeds.
On the positive side, spaying female dogs
if done before 2.5 years of age, greatly reduces the risk of mammary tumors, the most common malignant tumors in female dogs
nearly eliminates the risk of pyometra, which otherwise would affect about 23% of intact female dogs; pyometra kills about 1% of intact female dogs
reduces the risk of perianal fistulas
removes the very small risk (0.5%) from uterine, cervical, and ovarian tumors
On the negative side, spaying female dogs
if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common cancer in larger breeds with a poor prognosis
increases the risk of splenic hemangiosarcoma by a factor of 2.2 and cardiac hemangiosarcoma by a factor of >5; this is a common cancer and major cause of death in some breeds
triples the risk of hypothyroidism
increases the risk of obesity by a factor of 1.6-2, a common health problem in dogs with many associated health problems
causes urinary spay incontinence in 4-20% of female dogs
increases the risk of persistent or recurring urinary tract infections by a factor of 3-4
increases the risk of recessed vulva, vaginal dermatitis, and vaginitis, especially for female dogs spayed before puberty
doubles the small risk (<1%) of urinary tract tumors
increases the risk of orthopedic disorders
increases the risk of adverse reactions to vaccinations
One thing is clear much of the spay/neuter information that is available to the public is unbalanced and contains claims that are exaggerated or unsupported by evidence. Rather than helping to educate petowners, much of it has contributed to common misunderstandings about the health risks and benefits
associated of spay/neuter in dogs.
The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically mature, or perhaps in the case of many male dogs, foregoing it altogether unless medically necessary.The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Breed, age, and gender are variables that must be taken into consideration in conjunction with non-medical factors for each individual dog. Across-the-board recommendations for all pet dogs do not appear to be
supportable from findings in the veterinary medical literature.
I think these last paragraphs are very important, the information given to the public is typically skewed and one sided, especially on the recommended age to alter. Which is why mandatory spay and neutering sucks!!! People don't realize that their pets health are being put at risks and they may end up dumping a pet because of health problems that could of been avoided if the dog was allowed to mature more before being altered. How many female dogs may be dumped or euthanized because they are leaking all over the house? Or a dog gets cancer or some other health problem and the owner doesn't want to deal with or spend the money.
You can read the 12 pages and sources and decide for yourself whether you think they are valid and legitimate.