The role of endoplasmic reticulum stress in metabolic diseases and mammary epithelial cell homeostasis in dairy cows

High-yielding dairy cows undergo various physiological stresses during the transitional phase of the calving cycle. In this period, they experience negative energy balance, subjecting the liver to significant metabolic stress from an influx of nonesterified fatty acids. This metabolic stress not only impairs liver function but also diminishes milk production. Early lactation dairy cows may develop endoplasmic reticulum (ER) stress in the liver, potentially leading to liver-related diseases and contributing to ER stress in mammary epithelial cells, resulting in decreased milk production. Natural products that alleviate ER stress have been identified, and if further in vivo studies confirm their efficacy, they have potential as feed additives to prevent disease and reduce milk yield. Conversely, physiological levels of ER stress play a role in mammary gland development and positively influence protein synthesis in milk. Understanding the threshold level of ER stress in mammary tissue and its detailed mechanisms will be crucial in dairy farming.