Apologies in advance to those offended by the slightly off-topic,
non-human, yet paleo post.
Be warned there are references to doggie doo-doo ahead...

Hi Dori!

Yes, I have noticed this as well. My dogs have had the same experience when
switching  to their natural food. Prepared dog food -kibble- is designed to
form stools that are dry and "well-formed" (read -constipation) This is not
natural. Most of that "dog food" you put into your dog comes right back out
again. They use fillers such as corn and wheat which is indigestible. Stool
should be loose. However, since your killer chihuahua 's digestive tract is
used to processing the other stuff (grains mostly), it will take a period
of adjustment, as it does for all of us.
Bart is *not* used to *not* being constipated and it may take him some time
to gauge accurately when he needs to go. Reassure him, but don't make him
think it is OK to poop in the house. He is not breaking training,  just a
little perplexed. Give him extra potty breaks. And extra water. Bones (raw,
of course) will compensate for the runny stool by making it chalkier and
drier, and may give him more control. I would stop the canned food
altogether and let him make the full adjustment. Both of you will be much
happier once the transition is complete.
Email me if you want more detail...

Louise