2 according to the oxford english dictionary, cattle is the plural of cow in us english and cow refers to 'the female of any bovine animal'. However, it also mentions that cow can also refer to 'a domestic. The letter alpha originally represented a cow head.
Some words (ox/oxen, louse/lice) have kept their old plurals, and others have 'normalised' due to pressure on the language to be regular (cow/kine).