From the Super Mario Wiki
Chows are dog-like enemies that appear in Super Mario RPG: Legend of the Seven Stars in the region of Land's End. They have no weaknesses, but their stats are relatively low compared to the enemies present in the area and therefore, they do not pose much of a threat to Mario and company. A Chow also appears as a non-playable character in Monstro Town where he will give Mario a prize based on how many consecutive Super Jumps he can do, the prizes being Attack Scarf for thirty and the Super Suit for one-hundred. A weaker related species called K-9s appear earlier in the game. For some reason, they claim to have already fought Mario, as shown by their Psychopath thought. This may indicate that these are upgraded versions of the same K-9s Mario fought previously.