A ewe’s udder has two mammary glands or udder halves, each gland is lined with cells that produce milk. Milk collects in a reservoir above the base of the teat (the teat cistern), and as the lamb sucks the milk moves from the reservoir through the teat. The action of the lamb feeding stimulates the release of more milk that is sucked out immediately. During milking the teat end (sphincter) is open and can stay dilated for up to two hours, though the exact time can vary depending on muscle integrity. Ultimately this can provide an entry point for bacteria.
An optimum udder drops about halfway between the thigh and hock, with teats placed at approximately 4 and 8 o’clock (when viewed from behind). Ideally teats should not be too thick or long so that lambs are able to suckle easily. This conformation enables lambs to feed efficiently and avoid damaging the teats, and is associated with low levels of mastitis.