When right clicking and holding when spawning any breed-able Mob it makes multiple babies.This works with but not limited to Pigs, Sheep, Cows, Chickens, Wolves, Mooshroom, Ocelots and Villagers. I have been using this "method" to spawn many Villagers for miscellaneous reasons and it works with all breeding mobs.
1. Get out any Spawn Egg of the mobs above.
2. Right click to spawn the animal.
3. Hold it and many baby mobs of that mob will spawn only using one Spawn Egg.