[TxVicki]

Originally Posted by pstinard

The best time for spaying is after the growth plates close in the legs, but before the first heat if possible. The growth plates are the part of the leg that continues elongating, and if spaying is done before the growth plates close, the hormones are thrown out of whack and the legs grow longer than they should, leading to potential leg and joint issues. Typically, the growth plates are closed by 8 months of age. The smaller the Yorkie, the later the date of first heat cycle, so if your female is on the small side, I'd have the spay done at 8 months and hope she doesn't go into heat before then. If she does, you'll have to keep them physically separated until the heat cycle is over (typically 3 weeks). You can wait a little longer on the male if you want, but I'd have him neutered by 9 months to 1 year of age. Be sure to have retained baby teeth removed at the same time as the spay and neuter so they only have to be put under anesthesia once.

This is not always true. I know first hand.