Also if he and his lines are clear of the breeds health issues, some of which are listed here: Dealing with Your Chihuahua's Health Issues - For Dummies

Bitch owners often blame the stud if they produce defective puppies, but more often than not problems are likely to come from both sides.

You might like to read the article on this site http://www.petforums.co.uk/encyclope...ur_dog_at_stud