What are female longhorn cattle called?

Of course!! Longhorns (Texas Longhorns, English Longhorns, etc.) are not a specific gender or sex of cattle, it is a BREED, just like Angus and Holstein and Simmental and Jerseys are. As with ALL breeds of cattle, there are both males AND females in that particular breed. If that breed only has one gender or sex, that breed wouldn't even be considered a breed, and if it was it certainly wouldn't last very long!