Regulation of XXXX adipose tissue metabolism during lactation. 2. Lipolysis response to milk production and energy intake.

@entity1425 @entity1063 @entity291 @entity653
Lipolytic adaptations of @entity291 adipose tissue during late pregnancy, lactation, and dry period were studied in Holsteins. Treatment groups consisted of first lactation daughters of high or low bulls based on Predicted Difference for milk. Heifers were fed either a 60% concentrate, 40% hay diet or a 40% concentrate, 60% hay diet from 0 to 140 d lactation. Feeding a low energy diet for the first 140 d of lactation did not affect adipose tissue lipolytic rates measured in vitro. @entity1425 and @entity1063 responsiveness of @entity291 adipose tissue increased prior to parturition, increased further in early lactation, then remained elevated during lactation and into the dry period. This responsiveness was unaffected by feeding low energy diets. Basal @entity653 release in high genetic merit heifers was 64, 17, 40, 23, 20, and 42% greater than in low genetic merit heifers at -30, -15, 30, 60, 180, and 349 d about parturition. Response to @entity1063 was 15, 20, 18, and 15% greater in high genetic than low genetic merit heifers and response to @entity1425 was 12, 20, 14, and 50% greater in high genetic than low genetic merit heifers at 30, 60, 180, and 349 d postpartum. The lack of a dietary energy restriction effect on lipolysis in early lactation suggested that these rates were near the physiological maximum for those animals. Rates of lipolysis were positively related with milk fat production. This study indicates a genetic component in adrenergic regulation of lipolysis in adipose tissue, independent of energy balance, in supporting lactation.
