This briefly talks about effects on behavior:
http://docs.google.com/viewer?a=v&q=cacheiyOekL8AbwJ:www.andelrottweilers.com/prosandconsofNeutering.doc+pros+cons+spay+neuter&hl=en&gl=us&pid=bl&srcid=ADGEESisjicALzA_j73jhGhYWxBnxp8PNT8rnbxviysiuUcds71gzhnjgpmSHUBSp0UwKo4aiEiPQmZRVRSBUaZeBRSoe-hNIQYVaUObiMzaBET0UjcvnRbzmZTl2lXAa2FCnuI2A7Sv&sig=AHIEtbRxmEIu8Q-eAiD0H-pu4dPfiu-X_A
"Neutered male dogs and spayed female dogs are at increased risk of progressing from mild to severe
geriatric cognitive impairment compared to intact male dogs55. There weren’t enough intact geriatric
females available for the study to determine their risk.
Geriatric cognitive impairment includes disorientation in the house or outdoors, changes in social
interactions with human family members, loss of house training, and changes in the sleep-wake cycle55.
The investigators state “This finding is in line with current research on the neuro-protective roles of
testosterone and estrogen at the cellular level and the role of estrogen in preventing Alzheimer’s disease in
human females. One would predict that estrogens would have a similar protective role in the sexually intact
female dogs; unfortunately too few sexually intact female dogs were available for inclusion in the present
study to test the hypothesis”55"
http://www.naiaonline.org/pdfs/longtermhealtheffectsofspayneuterindogs.pdf
"Those behaviors that are not sexually dimorphic, including most forms of
aggression, are not decreased in incidence by gonadectomy. One behavioral
consequence of spaying that has been documented in several studies is an
increase in reactivity towards humans with unfamiliar dogs and increased
aggression toward family members. This may be hormonally related; there may
also be a breed predisposition."
http://www.akcchf.org/news-events/library/articles/issue25spring2008.pdf
"The study that identified a higher incidence of cranial cruciate ligament rupture in spayed or neutered dogs also identified an increased incidence of sexual behaviors in males and females that were neutered early.(5) Further, the study that identified a higher incidence of hip dysplasia in dogs neutered or spayed before 5 1/2 months also showed that early age gonadectomy was associated with an increased incidence of noise phobias and undesirable sexual behaviors.(6) A recent report of the American Kennel Club Canine Health Foundation reported significantly more behavioral problems in spayed and neutered bitches and dogs. The most commonly observed behavioral problem in spayed females was fearful behavior and the most common problem in males was aggression.(12) "
http://www.caninesports.com/SpayNeuter.html
This talks about aggression and effect of altering:
http://docs.google.com/viewer?a=v&q=cache:MIsMmQvf464J:eprints.lincoln.ac.uk/1880/4/1_3.pdf+increase+same+sex+aggression+spay&hl=en&gl=us&pid=bl&srcid=ADGEEShbmkW6bI5lTELpyYLhEHTB1Ip1M3qvE_Hzwc9w1RU-9RdlF-28WXRzrKWSOUSqAghEs7Wy7wGbChNVwBD2HGunHnnSbA91rd18OowAUGr-g20zXbeCPCi_xQE5DCHg96ONgW26&sig=AHIEtbTrw_TYnS37EgsoGg1nqFOTg-tARg
"The results of the study suggest that spayed female dogs tend to be more aggressive
toward their owners and to strangers than intact females, but that these effects of spaying
on behavior appear to be highly breed-specific. Contrary to popular belief, the study
found little evidence that castration was an effective treatment for aggressive behavior in
male dogs, and may exacerbate other behavioral problems. Further research will be
needed to clarify the relationship between age of spaying/neutering and these apparent
effects on behavior.
Reference
Hsu, Y., and Serpell, J.A. 2003. “Development and validation of a questionnaire for
measuring behavior and temperament traits in pet dogs.” J. Amer. Vet. Med. Assoc., 223:
1293-1300."
http://www.cdoca.org/downloads/files/Early%20SN%20and%20Behavior.pdf
Effects of spaying on reactivity in female GSDs:
http://www.scribd.com/doc/14286225/Effects-of-Ova-Rio-Hysterectomy-on-Re-Activity-in-German-Shepherd-Dogs
Evidence Based Vet Forum, lots of studies involving altering posted here:
http://www.ebvet.com/forum/viewtopic.php?t=15