Lactation Physiology
The process by which mammary glands produce and secrete milk is referred to as lactation. Lactation requires synchronous physiological processes to maintain the homeorhesis of the dam and nutrient acquisition essential for milk formation.
It is the most important and expensive phase in dairy animals. The lactation length is about 305 days in cattle, and it varies in different species. Mammary glands are the organs in mammals that produce milk for the sustenance of the young. Mammary glands are among the few structures in mammals that may undergo recurrent growth cycles, functional differentiation, and regression. The mammary gland is derived from the ectoderm during the embryonic stage. Mammary glands include teats, duct systems, lobes, lobules, and secretory tissue. Between puberty and parturition, the formation of ducts and milk-secreting tissue occurs. Mammary gland is modified sweat and exocrine glands, located in the inguinal region in sheep, cattle, goats, horses, and whales; thoracic region in primates and elephants; ventral surface of both thorax and abdomen in pigs, rodents, and carnivores. Delicate membranes separate the front and rear quarters. In cattle, rear quarters produce almost 60% of the milk, while the forequarters produce the remaining 40% and a lactating udder weighs around 15-32 kg. Many factors regulate milk production like age, breed, environment, hormones, and many more.The process of synthesis and secretion of milk from the mammary alveoli is called lactogenesis. Alveoli are the grape-like clusters containing epithelial cells that absorb nutrients from the blood, transform them into milk, and discharge the milk into the alveolar cavity. Blood supply to the mammary gland is extremely important for its function. Did you know, for every litre of milk produced by a dairy cow, almost 670 L of blood flow through the udder? Further, several hormones play a major role in development of mammary gland and maintenance of milk secretion throughout lactation period. The physiological mechanisms that regulate milk production in cows are multifaceted and extensive.
Several cascades and hormonal cycles in the cow’s body favour the beginning and termination of milk production. Hence, the lactation stage in the life cycle of a dairy cow is extremely vital considering the production and economic conditions.Recently, the mammary gland has been considered a bioreactor in a crude way. The mammary gland is like a factory that produces remarkable proteins. So how about genetically engineering the mammary gland after understanding the basic physiology to produce the proteins that are not produced in the mammary gland necessary for consumption. The result of this challenge is transgenesis. Using this technique, we can make the genetically engineered calf harvested for nutraceuticals or bioactive components. This concept is still under research, but the technique offers opportunities to produce milk ideally suited for a particular product, for example, milk specifically produced for cheese. This technique is challenging to harvest from human blood because of its lower concentration. Those proteins can be produced through the mammary gland of animals ranging from rabbits to cows. Anticlotting agents and drugs used to treat angioedema, emphysema, wound healing, and haemophilia have been successfully harvested. Coming to small ruminants, it is now easy to produce monoclonal and polyclonal antibodies that can be used in diagnostic products through genetically modified goats. Most people are lactose intolerant, but no worries; it can be countered by knocking out the α-lactalbumin gene, which drastically reduces the lactose concentration in the milk. Mastitis is the most significant setback in the dairy industry; a study conducted in cows found that a gene encodes lysostaphin in cow’s milk to protect against Staphylococcus aureus mastitis.
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