I have a Pedigree Minature Yorkshire Terrier, she is only 13wks. I'm not sure if I will breed her in the future but I am gathering info to determine this? I have had a fair bit of info on the ideal weight to breed a Yorkshire, some of the feedback is that if she weighs less than 5lb when adult she is not able to be bred, is this true? I work in a Veterinary Surgery and each Vet has different opinion, I have experienced many C sections in Chihuahuas as to save all the pups and they have weighed less than 5lb. Even dams that have given birth naturally with no problems have weighed less than 5lb, why so different for Mini Yorkshires? Also, Japanese Chins can weigh less but are still bred? I would appreciate some more feedback as I said she is very young but if I don't breed than she will be neutered at 6mths, I have to see what her temp and comfirmation is like when she is adult if I will breed or not. So am very early in asking this...
Thanks very much for taking time to read this :.)

Actually, there's no such breed as a 'Miniature' Yorkshire Terrier. ;) There's only one Breed Standard which has the weight is up to 7lb. However, reputable Yorkie breeders will breed smaller dogs to larger bitches, for the health not only of the bitch and pups, but also for the good of the breed. The very tiny ones generally have many more health problems and aren't nearly as robust as the somewhat larger ones.

You may find this site helpful - I haven't read it all, and it's American, but the many of the same principles apply to the UK ...

As your experience shows, the very small bitches tend to need c-sections, and that's never to be taken lightly. Chihuahuas of up to the standard weight (6lb) usually whelp naturally.