MAMMARY GLAND IMMUNITY
The secretions of the mammary gland create an environment that can support bacterial growth if bacteria manage to enter the gland. The immune function in the mammary gland differs from other parts of the body and may be compromised at various stages of lactation.
Most new infections in the mammary gland occur through the streak canal, so the primary defense of the immune system in the mammary gland relies on anatomical and physiological barriers. The smooth muscle of the teat sphincter closes the entrance to the streak canal, preventing bacterial entry. However, there are instances, such as immediately after machine milking or during decreased muscular activity due to periparturient paresis, when sphincter activity decreases, allowing easier access for microorganisms.Similar to other body parts, the skin lining the teats and udder, as well as the streak canal, act as physical and chemical barriers against bacterial invasion. These areas have a natural bacterial flora that inhibits the colonization of bacterial pathogens. Additionally, the surface of the streak canal is lined with keratin, which contains antibacterial lipid and protein compounds. Keratin binds bacteria to its surface and is shed during milk secretion, carrying away bacteria. Furthermore, keratin desiccation can lead to the formation of a plug in the streak canal during non-lactating periods, blocking bacterial entry. Many of these primary anatomical and physiological defense mechanisms are genetically determined, including udder and teat characteristics such as size, shape, length, end shape, placement, udder depth, teat sphincter function, and keratin production.
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