There are two genders - male and female. Although certain genetic disorders and mutations can alter the characteristics of these genders, there are no genders other than male or female, which are opposites. "Colt" is neither "male" nor "female"; therefore, gender wise, "colt" has no opposite.
The complimentary sex to a colt is a filly. Horses do not understand the concept of gender though and therefore there is no "opposite gender" to a horse or any animal including humans. Gender is a part of a humans identity and there is no opposite to that. Sex on the other hand refers to chromosomal characteristics. While sex for many animals includes XX and XY but there is much more to that including XXX and XXY.
Doctor is a neuter gender
Opposite gender of Filipino: Filipina
Clot is not gender specific.
Opposite gender of a Filipino: FILIPINA
The opposite gender of farmer is farmeress or farmwife.
An emperor is the opposite in gender to an empress.
The opposite gender of fraternity is sorority.
The opposite gender of giantess is giant.
The opposite gender for Joseph is Josephine.
The opposite of dairymaid is dairyman.
A Printe is the opposite gender of Printecess
Cock's opposite gender is hen.