Growth, Development and Involution

Mammary gland development and lactation occur in cycles during a cow's life. The presence of a mammary fat pad and other stromal components of the mammary tissue is important for the development of the epithelial structures in the gland. Some mammogenic hormones act through their effects on stromal tissue, leading to secretion of growth factors, which in turn control epithelial development. High blood concentrations of estrogen and progesterone, synergizing with other mammogenic hormones, stimulate the exponential growth of lobular structures and development of alveoli within the lobules that occur during pregnancy. When milk removal is stopped at the end of lactation, the gland undergoes a process of involution, which returns the tissue to a nonlactating state that is prepared for the next cycle of mammary growth, lactation, and regression. Current studies using genome-enabled (transcriptomics, proteomics, gene silencing) technologies will contribute to a greater understanding of the regulation of growth at each phase of mammary development, as well as to our understanding of the relationship among the developmental phases.