A righteous man regards the life of his animal, but the tender mercies of the wicked are cruel.
King Solomon recognized that a righteous person will not only treat his fellow man kindly, but will also care for his animals. It seems the implication is that the godly person shows more kindness to animals than a wicked person shows to other people—even on a good day. We should treat animals—and people, especially—with compassion, not cruelty.
For more about practicing kindness, see “Fruit of the Spirit: Kindness.”