It can be done at 4 months, but I wouldn't recommend that. Several reasons...most important being the weight. A 4 month old Yorkie usually is less than 5 lbs and the more you let them grow and gain weight, the better it is on their little bodies to go under the anesthesia.
Some people do it at 6 months...this is standard in almost all breeds. I think spaying females before their first spay is the reason for this timeline. Not sure it really matters with a male's neuter (except to stop any marking he is doing).
However, with Yorkies, I suggest waiting until 8 months because Yorkies retain baby teeth often. By 8 months, you'll know if they have been all lost or some still remain. If some still remain, they can be pulled while under the same anesthesia as for the neuter/spay. The less often you have to put a little under anesthesia, the better.
__________________ Terri, proud mom to Mandie  & Shelby-Dale  |