The growth and development of the mammary gland starts before the animal is born. The development is especially fast during puberty and gestation. The endocrine system coordinates the development of the mammary gland with the reproductive system and the metabolic needs of their offspring. The development of the mammary gland before it starts producing milk is called mammogenesis. Crucial hormones for mammogenesis are: growth hormone, IGF-1, glucocorticoids, thyroid gland hormones and sex hormones. For its development during pregnancy progesterone, estrogen, prolactin growth hormone, placental lactogen, insulin and corticosteroids are of great importance. Lactogenesis is the beginning of milk production. The first milk that the mammary gland produces is called colostrum. The process of maintaining milk production is called galactopoiesis and during that process the number of epithelial cells and milk production are correlated. Lactogenesis is primarily controlled by prolactin, and milk ejection is dependent on oxytocin. Prolactin has many biological functions inside the organism and it is released by the anterior lobe of the pituitary gland. Its main function is expression of genes necessary for milk protein synthesis. Oxytocin is most important for the contraction of myoepithelial cells that are found on the surface of alveoli and milk ducts. Oxytocin is secreted in a pulsating pattern. Other hormones that are important for lactogenesis are: cortisol, which has a general effect on the animal’s metabolism, progesterone whose function is stimulating the development of the mammary gland prepartum, growth hormone, estrogens which are important for the production of prolactin receptors and they increase the secretion of prolactin. Most of the organic milk compounds are synthetized only in epithelial cells of the mammary gland. The four main constituents of milk are proteins, fats, lactose and minerals. We can also find vitamins and other molecules which are taken from blood by the mammary gland. Epithelial cells have a very fast metabolism. Main proteins found in milk are caseins, whey proteins, immunoglobulins and enzymes. Standard cattle lactation lasts 305 days. Peak of the lactation curve is observed 4-6 weeks after giving birth. If the udder is not emptied properly, milk production will drop because alveoli and secretory tissue of the udder will undergo the process of involution. After weening off their young the mammary gland goes through the process of involution. It is also controlled by hormones.