[Amazing Yorkies]

Even more important than personality change, you need to protect your Stud male from a Canine Venereal Disease, called Brucellosis. A blood test of the Female needs to be taken before any Studding takes place. A test takes about a week to come back, so plan ahead.
This only applies to Females that have been exposed to other males in the past, but I insist on a test even with New females, just in case. It's not worth it. Then the male spreads it to all females he comes in contact with. Puppies are either born dead, or die shortly after death, but a female with Brucellosis will never have babies live.
A-I is also a protection.
I have found that Stud males get more aggressive with other dogs, but just as loving to it's owners. They do get a little restless though, LOL