Playing the name game can be confusing. Remember the pre-political correct days. In some ways they were much more simple. In fact, they are on the tail end of the movement. There was much more fanfare when the Lady Huskers became the Huskers.
Opinions vary on why things change.
There are options. Some schools have taken other approaches. While a mustang can be either male or female, the Sutton boys are the Mustangs, but the girls are the Fillies. But the Milligan Roosters and Crawford Rams have gender-sensitive mascots. I don't ever recall hearing of the Milligan Hens and the Crawford Ewes.