In seasonal animals, the process of triggering and maintaining lactation requires numerous hormones. The interaction of growth factors and other hormones is necessary in processes such as mammogenesis, lactogenesis and galactopoesis. Due to the proper synchronization of pregnancy and changes in the area of the mammary gland, the gland is ready for the production of milk at the moment the offspring is born. Mammogenesis is a phenomenon that requires the participation of a number of hormones, including prolactin (PRL), growth hormone (GH), estrogens, progesterone, oxytocin, placental lactogen (PL) and insulin-like growth factor (somatomedine, e.g., IGF1). The co-participation of IGF and GH is necessary in coordinating the differentiation and proliferation of epithelial cells. The manner in which the growth factors stimulate or inhibit the growth of cells or their influence on the cell cycle is not fully understood. The role of IGF in particular stages of functioning of the mammary gland (mammogenesis, lactogenesis, galactopoesis, desiccation), particularly in the case of ruminants, is highly complicated. Recently, attention has been given to the metabolic hormones, particularly the role of leptin in mammogenesis, lactogenesis and galactopoesis. The discovery of the leptin mRNA in mammary gland cells of many species, including humans, suggests that the mammary gland in itself may be the structure producing leptin. Leptin is the paracrine factor that influences the growth, development and functioning of the mammary gland by interacting with leptin receptors in areas of epithelial tissue. Due to the recently increased interest in sheep’s milk products, an understanding of the endocrine mechanisms facilitating the maintenance of lactation during autumn and winter may contribute to the improved profitability and usefulness of sheep’s milk.
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