Spell 1: Impregnate
Do it however you want, but it needs to be a single target spell.
Spell 2: Pregnancy
Modified Brilliance Aura that affects only the unit that has the ability
Female sheep: No mana regen, no abilities
Male sheep: has Impregnate ability
Baby sheep: whatever
Don't have WE in front of me, but here's the basics:
Trigger 1
Events
A unit starts the effect of an ability
Conditions
Ability being cast is equal to Impregnate
Actions
IF
target unit of ability being cast is of unit type (Female Sheep)
THEN
Set target unit of ability being cast mana to 0
Give target unit of ability being cast Pregnancy //the spell described earlier
ELSE
Display to Owner of Casting Unit "I don't think it works that way..." // just in case someone decided to target a male sheep or a person,, etc.
Trigger 2
Events
Every 1 second of game time
Conditions
Actions
Pick every unit in playable map area matching (unit type of matching unit is equal to female sheep) and (matching unit mana is equal to 100% of max mana).
-Loop
Set mana of picked unit to 0
Create baby sheep at location of picked unit
Remove Pregnancy from picked unit
Anyway, something like that should do it. Make sure to fix leaks and all that, and good luck...