I got the following sloka in Sri Sri Sitarama-Kathamrita, a collection of gospels of Sri Sitaramdas Omkarnath, by Kinkar Brahmanda (page 27):
kukkuta-swana-marjaran poshayanti dinatrayam/
iha janmani sudratwam mriah swaa chaavijaayate//
If a twice-born keeps cock, dog or cat as pet for three consecutive days, he becomes sudra in this birth and born as dog in the next birth.
Could someone provide the source of this sloka?