The role of heat stress in goat mammary gland development and milk production.

Global warming has increased the frequency, intensity, and duration of extreme climatic events and has thus increased the exposure of dairy animals to heat stress. As a result, heat stress has become a major challenge for dairy production because it negatively affects animal health, welfare, and productivity. In addition, it can impair mammary gland development and compromise both milk yield and milk quality. In dairy ruminants, heat stress impairs mammary function by altering the proliferation and apoptosis of cells in mammary tissue, particularly during dry periods and early lactation. Considerable progress has been made in understanding the physiological effects of heat stress, but there is insufficient information about the complex interactions between heat stress, cell apoptosis, and milk synthesis in dairy goats. In particular, there is limited information about the effects of heat stress on the turnover of mammary epithelial cells (MECs) during lactation. This knowledge gap is especially evident for dairy goats as relatively few studies have investigated the effects of heat stress on their MEC proliferation, differentiation, and survival. These cellular processes are essential for mammary development and function, and their disruption may impair cellular metabolism and ultimately reduce milk synthesis. Therefore, this review summarizes current knowledge about the effects of heat stress on physiological responses, mammary gland development, milk quality, and milk yield in dairy goats. In addition, the cellular mechanisms that regulate milk synthesis by MECs are discussed, and potential pathways through which heat stress may impair mammary function are highlighted.