There are scads of slang, sometimes demeaning, terms used to refer to women. It is usually easy to figure out where most of these metaphorical connotations originate . . . chick, fox, bird, kitten, and yes, even, bitch. Note the references to animals.
There are others with non-animal metaphorical connotations of course . . . dame, darling, babe, baby-doll, sugar, honey, and broad.
Most of those have easily recognizable origins . . . all except ‘broad’. It’s not particularly self-evident . . . most women aren't particularly broad. I thought it might have something to do with that women are broader in the hips than their male counterparts. But in that sense it wouldn’t necessarily be a derogatory reference. Many men are attracted to hippier women . . . evolutionarily speaking, hip width has very high correlation to female fertility, thereby unknowingly guiding men's evolutionary choices.
But the term generally is not used as a complimentary term. In fact, the word ‘broad’ usually refers to a large, loud, crude woman.
So where in the heck does the word come from? You may be surprised to learn that ‘broad’, as it refers to women, is indeed an allusion to an animal. A ‘broad’ is what a pregnant cow is called.