Gene expression in liver and adipose tissue is altered during and after temporary changes to postpartum milking frequency

摘要

Short-term changes to milking frequency can alter the metabolic status of dairy cows depending on the duration, magnitude, and stage of lactation at which the milking frequency changes occur. Additionally, effects of altered milking frequency that are subsequent to cows returning to a normal twice-daily (2 ×) milking regimen are not well established. This study tested the hypothesis that plasma concentrations of key hormones and metabolites and transcription of genes involved in the somatotropic axis and lipid metabolism would be altered in liver and subcutaneous adipose tissue from cows milked with different frequencies. Multiparous Holstein-Friesian dairy cows were allocated to 2× milking for the whole lactation, or once-(1×) or 3 times-(3×) daily milking for 3 or 6 wk, immediately postpartum, and then 2 × milking for the remainder of the lactation. Liver and subcutaneous fat were biopsied at wk 1 (liver only), 3, 6, and 9 postpartum, and transcription of genes involved in the somatotropic axis and lipid metabolism were measured. At wk 3, cows milked 3× had lower hepatic expression of growth hormone receptor (GHR1A) compared with cows milked 2 × or 1 ×, and lower IGF1 expression compared with cows milked 1×, indicating greater uncoupling of the somatotropic axis. At wk 6, reduced transcription of total GHR and GHR1B occurred in the adipose tissue of cows milked 3 ×. Cows milked 1 × had greater transcription in adipose tissue of lipogenesis genes at wk 3 and 6, and lipolysis genes at wk 6, compared with cows milked 2x, indicating a period of increased fatty acid storage, followed by increased fatty acid reesterification. At wk 9, cows previously milked 3 × for 6 wk maintained lower transcription of genes involved in lipogenesis, lipolysis, and ketolysis in adipose tissue compared with cows milked 2 ×, indicat- ing that the effects of 3 × milking persist for at least 3 wk after switching to 2 × milking. Results indicate that alterations to milking frequency affect the transcription of genes involved in lipid mobilization and storage, enabling the animal to manage the energy demands associated with the change in milk production. Some of these gene transcription changes were maintained in cows previously milked 3×, indicating that the adipose tissue gene expression changes were still required even after 3 wk of the less-demanding 2× milking regimen.