When my Mom was a kid, she had a Chihuahua named Lilly... my Grandfather left her in the backyard to go potty, and the nieghbors Yellow Lab jumped the fence and bred with her - he found them, er, tied. They brought her to the vet, but she delivered 4 puppies naturally without complications. The pups looked basically like 20-lb labs, except they were spotted because Lilly was spotted