Here is some more info:http://www.winnfelinehealth.org/repo...ly-neuter.html
"Critics have claimed several possible detrimental side effects from early neutering. It is commonly believed that neutered animals are less active and more prone to obesity than unaltered animals. It was also suggested that neutering at an early age would stunt normal growth. In male cats in particular, it was feared that early castration would affect the development of the urinary tract and lead to an increased incidence of cystitis or urinary obstruction.
Observations of urinary tract development showed no differences between the three groups other than the differences related to sex and these were consistent across all groups. The investigators measured the diameter of the urethra in the male kittens only and found no differences between the groups.Concerns have been raised that early neutering would result in smaller diameters in the urinary tract, resulting in an increased incidence of cystitis and related problems. This does not appear to be the case.
The main differences observed between the groups occurred in the comparison of secondary sex characteristics. Males were examined for differences in the development of the penis and prepuce (skin covering the penis), as well as for the development of penile spines. The penile spines were absent in Group 1, smaller than normal in Group 2, and normally developed in Group 3. In the examination of the female kittens, investigators found that the vulvas were more infantile in Groups 1 and 2 and normal in Group 3. None of these differences had any impact on the ability to catheterize the kittens. Concerns that development of the urinary tract might be arrested or impaired by early spaying and neutering proved unsupported.