Here's some info I found . It's from a breeder's website but isn't the breeder's words. The work is referenced so I would suppose it could be verified. Anyway, here it is....(written by Pam Davol, a noted research scientist and a genetic expert)
"Owners who are considering neutering need to take all factors into consideration, not simply the benefits of neutering when making a decision as to when to neuter.
If one looks close enough, one will find that neutering is one of those topics in veterinary medicine that is extremely biased: that is, most often one will find more emphasis placed on the pros of neutering with more often than not, very little or no discussion of the cons. Veterinarians, and responsible breeders as well, face a true dilemma when discussing neutering. The overpopulation crisis presents a very real concern with regard to the necessity of ownership responsibility. Prepubertal/early neutering or required neutering provides a means for vets/breeders to enforce owner responsibility by ensuring surgical sterilization of dogs not destined to be used in breeding programs. Again, this enforced neutering is typically presented along with a preamble of all the benefits that go along with neutering. However, I believe that breeders, if not veterinarians, need to begin questioning the ethics of this approach to prompt or require owners to neuter; especially in light of the facts that early neutering may not be as benign a process to the health of a dog as one would believe.
Yes, neutering prior to the beginning of estrus does reduce risk for mammary cancer in females, but it also significantly increases risk for urinary incontinence in bitches which predisposes these bitches to diethylstilbestrol (DES) dependency (Stocklin-Gautschi et al., J. Reprod. Fertile. Suppl. 57:233-6, 2001 and many other references)--in some instances, DES is not effective at controlling incontinence and will force some owners to elect euthanasia. Though with lesser risk compared to females, early neutering also increases risk of urethral sphincter incontinence in males (A. Aaron et al., Vet Rec. 139:542-6, 1996.)
With regard to cancer, spayed females have a 4 times greater risk for developing cardiac hemangiosarcomas (vascular tumors) compared to intact females (neutered males also show a significant increase in risk for these tumors compared to intact males) (Ware and Hysper, J. Vet. Intern. Med. 13:95-103, 1999.). Additionally, both neutered males and females have a 2-fold greater risk for developing bone tumors (osteosarcoma) compared to intact males and females (Ru et al., Vet J. 156:31-9, 1998.).
Some evidence suggests that early neutering may also predispose to endocrine disorders later in life (Panciera DL. J. Am. Vet. Med. Assoc., 204:761-7 1994.). Furthermore, there is also an indication that early neutering (because absence of sex hormones delays maturation of osteoclasts and thus results in delayed closing of the growth plates in the long-bones) may predispose to increased risk for various orthopedic disorders (such as cruciate ligament disease as I had mentioned in a previous post). Also, some evidence suggests that there is a correlation between increased time for growth plate closure and incidence of HD in Labs (Todhunter et al. J. Am. Vet Assoc., 1997).
If one conducted a research of the literature on the detrimental effects on physiological development associated with sex hormone deficiencies during adolescent development in any other species other than the dog and cat, one will find a wealth of literature stressing the importance of sex hormones for sound physiological, endocrine and metabolic development. Additionally, if one examines the scientific research that reports the benefits of early neutering in absence of any side-effects in dogs, one will discover that the methodology of these studies are designed in very specific ways to assure that outcome in neutering is presented in a favorable light (this does not mean that the data is biased, this simply means that the comparisons made do not provide for adequate interpretation of long-term effects of neutering).
In light of this, though it is understandable for vets/breeders to urge dog owners to neuter their pets early with regard to the greater good (i.e. reducing risk of accidental breeding), the physiological soundness of the individual dog should take precedence over any other issues. As such, it is my opinion, based upon the literature that I have reviewed that to reduce risks to physiological soundness, etc, that I am of the personal opinion that dogs should be a minimum of 1 year of age before neutering" ....Here's the link the info's from..
ABOUT EARLY SPAY AND NEUTER