Most breed associations require 12 functional teats for pure bred registry. Sows do have supernumerary teats. This condition can be on one or any number of nipples. Blood is supplied to the glands by two major arterial supplies. Venous drainage is parallel to the arteries.
Piglets suckle about every hour.
The anterior glands produce the most milk. The secretory apparatus of the breast consists of approximately 10 to 15 ducts extending from the nipple, and coursing through the mammary fat pad to terminate in clusters of alveoli. Each duct serves a specific lobule. Blood vessels, nerves and lymphatics run in the septae which merge imperceptibly with the fascia at the anterior thoracic wall. The areola serves as the termination point for the fourth intercostal nerve which carries the sensory information about suckling to the spinal cord and brain.