Abstract
Milk somatic cells (SCs) are a mixture of milk-producing cells and immune cells. These cells are secreted in milk during the normal course of milking and are used as an index for estimating mammary health and milk quality of dairy animals worldwide. Milk SC is influenced by cow productivity, health, parity, lactation stage, and breed of an animal. Any change in environmental conditions, poor management practices, and also stressful conditions significantly increases the amount of SC coming in milk. Better hygiene and proper nutrition help in reducing milk SC. Milk with low SC means better milk products with a longer shelf life. The present review describes the role of SCs (both secretory and immune) in milk, their role in maintaining the integrity of the mammary gland, and factors affecting their release in milk. This information may help to reduce milk somatic cell counts (SCCs) and to establish differential SCC standards.
Highlights
The udder or mammary gland has evolved in all the mammalian species to nourish their young one
The present review describes the role of somatic cells (SCs) in milk, their role in maintaining the integrity of the mammary gland, and factors affecting their release in milk
It was seen that there are significantly higher levels of bulk milk SCC (BMSCC) during the 12-month post-installation. These decreased over time and even showed a significant lower BMSCC after 36 months post-installation. These findings indicate that automatic milking had a negative impact on milk quality during the early stage
Summary
The udder or mammary gland has evolved in all the mammalian species to nourish their young one. The term SCs mean body-derived cells that are normally present at low levels in milk The majority of these cells in normal milk are cells from the udder secretory tissue (epithelial cells), and some are leukocytes (white blood cells). The cellular component includes the white blood cells (neutrophils, lymphocytes, and macrophages) normally present in a healthy udder and others that are activated by the immune system of the mammary gland [7]. To analyze the heritability of a trait and its correlation with udder health, group of workers examined the leukocyte populations of uninfected mammary glands and found that the effect of the cow trait is significant for neutrophil, macrophage, and T-lymphocyte-bearing CD4+ [11]. The invasion of pathogens to the internal tissues of mammary gland stimulates the trafficking of various immune cells to the site of inflammation which results in elevation of somatic cell counts in the secreted milk. Table-1: Morphological characteristics and percentage of different leukocytes in healthy and mastitis milk of different species
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