I have a boy and a girl, different litters and breeders. Both have been neutered. There is always someone at home, so they're never alone for more than a few hours, but they are great companions for each other. Besides, they tussle and tumble all over the place, which means *I* don't have to exercise them as much
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Having a pup of each sex allows you to see the differences in personality. Besides, little girls dress up SO nicely
Yorkies are like potato chips: Betcha can't have just ONE