Is it permissible to be mechalel Shabbos to save the life of an animal, such as a family pet? Could minchag, chumras, and/or purely Rabbinical prohibitions be relaxed in such a situation, and to what extent?
Please assume no Gentile is available to save the animal's life. However, if it would be permissible to relax certain rules in order to summon a Gentile for this purpose, please discuss.