CompFixedGender makes an animal always spawn with a given gender, either Male or Female

    //This comp class makes an animal always spawn with a given gender

    public Gender gender = Gender.Female;

It is a comp class, so you just add it in XML in the <comps> tag. For example, this allows Insectoid Queens in Vanilla Factions Expanded - Insectoids to always spawn as Female

<comps>		
	<li Class="AnimalBehaviours.CompProperties_FixedGender">
		<gender>Female</gender>
	</li>
</comps>