Regulation of bovine adipose tissue metabolism during lactation. 7. Metabolism and gene expression as a function of genetic merit and dietary energy intake

The regulation of adipose tissue metabolism is critical to the efficient establishment and support of lactation, through both energy supply and several endocrine and cytokine factors. We still lack detailed knowledge of the role of transcription and posttranslational regulation of metabolic flux. We need to quantitatively understand the genetic and environmental (primarily dietary) regulation of adipose tissue to help improve productive efficiency. Therefore, objectives of this project were to help define mechanisms of adipose tissue responses to lactation and energy deficit, including changes in gene expression and their relation to changes in metabolic flux and production. A total of 48 cows were selected for genetic merit based on sire predicted transmitting ability of milk. From 21 d prepartum to 60 d in milk (DIM), cows were fed to energy requirements or to 90% of energy requirements, with content of protein, vitamins, and minerals balanced to be the same for both treatments. Adipose tissue biopsies were taken at 21 and 7 d prepartum and 7, 28, and 56 DIM to determine rates of lipogenesis and lipolysis, and to measure gene expression of proteins controlling lipolysis. The cows on the restricted diet consumed 12% less feed prepartum and 16% less feed postpartum and dietary energy restriction decreased milk production. The slowest rates of lipogenesis occurred at 7 and 28 DIM; higher-merit cows had faster rates of lipogenesis at 7 DIM but slower rates than lower-merit cows at 28 DIM. Energy restriction decreased lipogenesis. Basal and isoproterenol lipolysis increased with higher milk production and was relatively unaffected by dietary energy intake. The expression of genes controlling lipolysis were not affected by lactation and were slightly increased by dietary restriction, but were not well related to rates of lipolysis. These data confirm and extend previous work that regulation of adipose tissue metabolism in lactation is a function of both diet and genetic merit and is controlled by multiple mechanisms including gene transcription and posttranslational protein modifications.