In English language the words do not have genders as in other Indo-European languages. Despite this, some pronouns bear masculine, feminine and neutral properties as well. Among these pronouns "he" and "she" are used to refer to the humans whereas "it" is used for inanimate things as well as animals. Hereby, you are expected to call "dog" with "it". However, in vulgar language it is ok to call them with "he" or "she" in accordance with its gender. Besides, things like ships and airplanes can also be called as "she" in causal speech.