Effects of growing programs and beta-adrenergic agonists on gene expression in adipose tissue depots in finishing beef steers

Abstract

Scope and Method of Study:

As adipose tissue accretion in the bovine is controlled by a balance of adipocyte proliferation and differentiation; it is essential to evaluate how diet or the administration of exogenous compounds, such as beta-agonists, affects and/or regulates adipocyte proliferation in order to improve the quality of the beef produced. Knowledge and understanding of the relationships between mechanisms regulating metabolic and signaling pathways and other contributing factors which orchestrate adipose tissue deposition within and between adipose tissue depots could possibly be integrated into management practices in a value-based marketing system to produce a consistent and desirable product that would ultimately enhance consumer beef consumption, increase efficiency of production, and increase profitability for the beef industry.

Findings and Conclusions:

Gene expression profiles of bovine intramuscular and subcutaneous adipose tissue depots at the end of the growing and finishing production phases of cattle managed under different growing diets and the gene expression profiles of bovine intramuscular, subcutaneous, and visceral adipose tissue depots and Longissimus muscle tissue in cattle fed Zilpaterol hydrochloride the last 20 days of the feeding phase plus a 3-day withdrawal period was evaluated using microarray and validated using RT-PCR analysis. Three hundred sixty-eight array elements were observed to be differentially expressed between s.c. and i.m. adipose tissue depots in the Initial and/or one of the diets of the Growing Phase. Two hundred forty-eight array elements were found to be differentially expressed between s.c. and i.m. adipose tissue depots in at least one of the four treatment diets during the Finishing Phase. The data indicates the metabolic machinery for adipose tissue accretion was down-regulated in the i.m. adipose tissue depot compared to s.c. adipose tissue depot and the main effect of previous diet could possibly influence adipose tissue deposition at the end of both the growing and finishing production phases in beef cattle. Microarray analysis showed no array elements to be differentially expressed in the i.m., s.c., or visceral adipose tissue depots or Longissimus muscle tissue between the control steers and steers supplemented with ZH for 20 d with a 3-d withdrawal. Of the genes selected for validation using RT-PCR in respective tissues, only cytochrome C-1 and beta-AR 2 in i.m. adipose tissue and beta-AR 1 in s.c. adipose tissue did not support the results of the microarray analysis. RT-PCR revealed cytochrome C-1, beta-AR 1 and beta-AR 2 mRNA expression to be up-regulated threefold, fourfold and fourfold in zilpaterol -supplemented steers vs. control steers, respectively.