Concept:A mature female pig that has given birth or is used for breeding is called a sow.Solution:A gilt is a young female pig that has not yet produced piglets.A sow is an adult female pig that has bred or farrowed.Therefore, a breeding female pig is correctly called a sow.Key point: Doe is a female rabbit or goat, and heifer is a young female cow that has not calved.Answer:Option D (sow)