I agree with Christy's post - sounds more dominance related to me too.

FWIW we have two neutered females a border collie and a red heeler. BC is much taller and gentler but is also more jealous and still very puppy. RH is short and a bit more instinctive with things (like rounding up etc) and a few years older she came second as a rescue.

BC and RH often have fights that seem very agressive to me over nothing but noone is never seriously injured so to me seems more ego orientated. RH has pinned BC to the ground and had her by the throat to make her submit.

Other dogs on the farm (12 in total including our 2) often blue and sometimes there are small injuries and one in particular seems to bear the brunt all the time. They sort themselves out eventually though. Also season seems to play a part in their bickering even with the neuted ones.