Originally Posted by jaycee
it affects the way their bones grow, they grow faster and wind up growing longer than they would have so your cat would be slightly bigger than it would have been. no, its not a gross deformity but since it does affect them i would rather wait if possible, until they are between 5-6 months which is right BEFORE they mature sexually.
Actually this isn't true. Early spay/neuter has been around for over 20 years now and they have done a lot of research about the differences between early speuters, later speuters and unfixed cats. It's a common enough practice for the medical community to study it now.
The only difference in size that has been noticed is the fullness of their heads, and that is primarily in males. A never fixed male will have that full tom-cat head. A later neutered male's head will be much smaller, and in some cases (not all cases) an early neutered male's head will be slightly smaller than a later neutered male's head. It's not really the size of the bone structure, but the fullness in the cheeks.
Some of the largest cats in my house were neutered at 8 weeks old and haven't even noticed the head size difference. Some of my later neutered males are quite smaller.