Cellular changes in lipid metabolism in response to altered energy balance and heat stress in lactating dairy cows
The dairy industry has evolved through the years. There is a need to continuously improve on selective breeding programs and management strategies in order to produce superior animals that could meet the increasing demands for food as well as adapt to the changing environment. Currently, a substantial amount of research has focused on the metabolic and physiological adaptations observed in dairy cows, particularly involving changes in energy balance during lactation. Studies described herein are designed to elucidate metabolic changes in the lactating cow, with particular regard to adipose tissue metabolism, and determine how these changes observed at the cellular level could potentially contribute to the animal's adaptive process. Study 1 focused on the regulation of lipolytic proteins in 2 different models of altered energy balance achieved via feed restriction and growth hormone administration. Data show that multiple mechanisms regulate lipolysis, resulting in changes in abundance and phosphorylation of various lipolytic proteins. Study 2 evaluated the direct impacts of heat stress on lipid metabolism in vitro, relative to the presence of a beta-agonist and insulin. Results suggest that acute heat stress directly increases the response of primary bovine adipocytes to lipolytic but not lipogenic stimuli, and that increased insulin sensitivity observed in heat-stressed cells may potentially contribute to the diminished lipolytic response observed in vivo.