Have ewe got cleavage! Tips on sheep udders and teats.

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The Ovine mammary gland is an intricate structure composed of secretory tissue (Parenchyma) and supporting ligaments, venous, lymphatic, adipose and nervous tissue (Stroma). There are two mammary glands divided by a suspensory ligament contained within the udder as shown in the Ovine udder anatomy diagram.

Mammary Gland Development

The development of the mammary gland (mamogenesis) commences in the embryo and continues through to lactation. Ewe lambs are born with cistern, teats and some large ducts. Alveoli and interlobular ducts develop several months after birth along with fat and connective tissue. During pregnancy and in response to estrogen and progesterone, the concentration of blood vessels and secretory cells increases, with new alveoli and duct formation continuing for several weeks post lambing.

Lactation

In the last trimester of pregnancy, changes in the concentration of circulating hormones and growth factors induces lactogenesis, enabling milk production. Nutrients, white blood cells and antibodies are transported to the secretory alveoli by surrounding blood vessels and lymphatic tissue. The secretory epithelial cells produce milk particles from the nutrients absorbed from stromal tissue. Milk globules, composed of milk particles and cytoplasmic fluid, are moved to the inner lumen by pinch off part of the cell wall in a process known as apocrine secretion. In response to external stimuli, nerves innervating the udder signal the release of oxytocin from the brain, which acts on the myoepithelial layer causing the alveolus to contract and forcibly expel milk from the lumen into the network of ducts and down to the gland cistern. Suckling or manual milking causes milk to pass through the annular ring into the teat cistern where it is ejected from the teat through the streak canal. Shortly after milking, the teat sphincter closes preventing milk leakage and infection.

In sheep and goats approximately 50-70% of the milk is stored in the glands cistern unlike 20% in cattle. Sheep with larger gland cistern can store more milk and cope with less frequent milking, which is beneficial for dairy sheep.

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