That is definitely not normal -- I have never heard of a cavalier that small at adult size that didn't have some underlying health cause for that size. But. on the other hand, perhaps she is just surprisingly small, or there's actually some smaller-breed genes in her, for example? To be honest, though, I think you do need to at least be prepared to potentially have some health issue emerge at some point as the cause of this very small size -- a good breeder would generally have gone through potential issues with taking on such a very small dog, not told you (as you have said) that this was normal for the litter
. I wouldn't allow it to dominate your enjoyment at all, and she may live a perfectly happy, normal, healthy life, but I'd always be watching such a very small dog very carefully for any signs of any problems, and given her size, a really good vet or specialist might wish to do some basic tests to make sure there isn't some existing issue that could be addressed from the start. Vets can miss underlying issues and also may not be aware of how extremely small she is compared to breed standard.
Often, abnormally tiny size like this is caused by something like a liver shunt, or hydrocephalus, or open fontanels (the skull failing to close completely). As Nicki says, just as a general warning to anyone looking for a cavalier puppy, breeders who are deliberately aiming for very small cavaliers are to be avoided. Sadly, breeders who deliberately breed for extra small/'teacup' cavaliers do this by breeding extra small dogs -- meaning health-compromised runts, or dogs that are extra small because they have some underlying health issue.
The other possibility, depending on where the pup came from, is that this is actually a cross -- to a chihuahua, chin, papillon or other smaller breed. Some breeders are actually breeding many breeds of dogs and are not particularly careful of how they mix. A cross can come out looking exactly like a larger or smaller version of one of the breeds, with the second breed not apparent at all. So that is one possibility. If the breeder is a reputable, health -focused show breeder, then I'd certainly go back to discuss this puppy and her size with the breeder, as tiny size would be a major concern for a good breeder, who also would be there to offer excellent advice and support (that's the benefit of working with good show breeders
).
In short: if this were my dog, I'd go to the vet and explain the dog is less than half the size of the very bottom end of the breed standard (13-18lbs in the US) -- which is quite alarmingly small for the breed, even allowing for the norm for some dogs to be slightly under or over breed standard. I'd ask for a full health assessment and ask what can be tested if there is any obvious underlying, potentially treatable issue like liver shunt. I'd be moving proactively now. With something like liver shunt, this is very important -- she would benefit from monitoring tests (like a bile acid test) and a special low protein diet, for a start:
http://www.petplace.com/dogs/portosystemic-shunt-hepatic-shunt-in-dogs/page1.aspx
http://www.peteducation.com/article.cfm?c=2+2103&aid=882
I'd definitely have such a dog spayed too if she is not yet -- you would never want to risk putting her through an accidental pregnancy or risk carrying forward any of the potential health issues that could underly or be connected to severely small size.
PS I note from previous posts that your breeder sounds a bit worrying, as Lexy had many problems when you got her which the breeder said were not caused by her though obviously the pup could not have gotten any of those things 'after' as she claimed -- and also claimed such tiny size was 'normal' :yikes -- and she was diagnosed as a very young pup with hip dysplasia as well (if she has HD, this won't have gone away -- it will be a permanent condition for her -- thus would be surprised the vet would be saying she is 'perfectly healthy'
). If the vet is actually saying this about a young dog with HD and hasn't yet tested for any possible underlying issues, I'd change vets for a second opinion. And I'd never go near that breeder again.
I'd say given the sounds of the breeder that you may need to be on the lookout permanently for future possible issues, which is frustrating for an owner, but try to have that in the background, not foreground, and just focus on loving and caring for Lexy.
