Swine Prolactin (PRL) is a peptide hormone belonging to the prolactin/growth hormone family, which also includes growth hormone (GH) and placental lactogen–related hormones that regulate growth, metabolism, and reproductive physiology. In pigs (Sus scrofa domesticus), prolactin is produced primarily by lactotroph cells in the anterior pituitary gland and signals through the prolactin receptor (PRLR), activating intracellular pathways such as JAK2/STAT5, MAPK, and PI3K, which regulate gene expression and physiological responses. Swine prolactin plays a critical role in mammary gland development and lactation, supporting milk production necessary for neonatal piglet growth and survival. It also contributes to reproductive function, maternal behavior, and metabolic regulation, influencing processes such as corpus luteum maintenance and seasonal or endocrine regulation of reproduction. In pigs, prolactin can also affect immune responses and mammary gland physiology during the peripartum period. Because pigs are widely used as large-animal models for human physiology, endocrinology, and lactation biology, swine prolactin is studied in research on reproductive endocrinology, mammary gland development, and metabolic regulation, providing insights relevant to both livestock productivity and comparative biomedical research.