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Title: Influence of energy supply on expression of genes encoding for lipogenic enzymes and regulatory proteins in growing beef steers

Author
item MCLEOD, K - University Of Kentucky
item Baldwin, Ransom - Randy
item Connor, Erin

Submitted to: Beef Research Report
Publication Type: Other
Publication Acceptance Date: 7/18/2010
Publication Date: 9/20/2010
Citation: Mcleod, K.R., Baldwin, R.L., Connor, E.E. 2010. Influence of energy supply on expression of genes encoding for lipogenic enzymes and regulatory proteins in growing beef steers. Beef Research and Extension Report. Agr. Report SR-2010. pp. 161-167.

Interpretive Summary: We showed changes in expression of genes that control fat deposition in cattle are responsive to energy intake. Specifically, genes expressed in the fat present in the abdominal cavity are changed with alterations in the amount of energy consumed as well as the form of the energy (glucose or as starch and site of digestion (in the rumen or duodenum)) of the energy substrate presented. However, also in the abdominal fat depots, a clear relationship between genes which regulate fat synthesis and the genes which encode for known regulatory enzymes of the fat making process was not established. In contrast, changes in gene expression in the adipose tissue found under the skin were not affected by the dietary treatments. Finally, the relationship between the changes in gene expression we observed did not directly relate to observed changes in the animal's carcass. It appears that gene expression alone does not explain the observed increases in fat when these treatments were applied, thus other levels of regulation, such as substrate level interactions with proteins, are likely involved in controlling the synthesis of fat when carbohydrate intake is elevated.

Technical Abstract: Forty crossbred beef steers were used to determine the effects metabolizable energy (ME) intake and of site and complexity of carbohydrate (CHO) infusion on expression of genes encoding lipogenic enzymes and regulatory proteins in subcutaneous (SC), mesenteric (MES) and omental (OM) adipose. Treatments were a forage-based diet fed at 161 (LI) or 214 Kcal ME.(kg BW.75)-1.d-1, LI plus ruminal or abomasal infusion of starch hydrolysate (SH), and LI plus abomasal infusion of glucose. After 35 d, steers were slaughtered and tissue RNA was isolated from harvested adipose and used for quantitative realtime RT-PCR of selected genes. Although gene expression in SC was largely unaffected by treatment, expression in visceral adipose was highly responsive to dietary ME intake and CHO. Greater dietary ME intake increased expression of rate-limiting lipogenic enzymes and regulatory proteins in MES, but not OM adipose. Starch infusion did not alter gene expression in MES, however expression of lipogenic and regulatory proteins in OM adipose was greater when SH was supplied abomasally compared with ruminally. In both, the MES and OM adipose, abomasal glucose supply increased expression of lipogenic and regulatory proteins compared with abomasal SH supply. This study shows that dietary ME intake and site of digestion and complexity of CHO affect expression of lipogenic enzyme and regulatory genes of visceral adipose depots while SC adipose appears to be more resilient to dietary manipulations.