Originally Posted by
welsh
The cost of spaying after the first heat is higher because the blood vessels are more developed. Early spay reduces the risk of mammary cancer, which is relatively high.
Spaying before the first heat is associated with elevated risks of hip dysplasia and CCL injuries, and of certain cancers. In some breeds that are particularly prone to these cancers (Viszlas, Goldens), early spay is probably a bad idea for cancer risk alone.
Spay/neuter is also associated with several behavioral problems.
The last time I posted the UC Davis research on this, I got shouted down. I guess it depends who posts it.