Influence of zinc amino acid complex and ractopamine hydrochloride supplementation on the sarcoplasmic protein profile of finishing steers

Abstract Text: The objective of this study was to determine if Zn amino acid complex (ZnAA) and ractopamine hydrochloride (RH) supplementation affect the protein profile of the longissiumus dorsi muscle of finishing steers. Twenty-four steers (477 ± 5.3 kg; SD) were fed a corn-based finishing diet in pens equipped with GrowSafe bunks to measure individual intake, as a part of a 2×2 factorial of ZnAA and RAC supplementation. All steers were supplemented with 60 mg Zn/kg diet DM as ZnSO₄, and were assigned to receive either 0 (CON) or 60 mg supplemental Zn/kg DM from ZnAA (ZN; n = 12 steers per treatment) for 56 d. On d 56 steers were equally assigned within treatments to receive RH at 300 mg⋅steer^–1⋅d^–1 for 0 (NoRAC) or 28 d (RAC) prior to harvest (n = 6 steers per treatment). Muscle biopsies were collected from steers after 14 d of RAC supplementation. Four steers per treatment were selected to have sarcoplasmic extracts from muscle biopsy samples analyzed using 2D Difference in-Gel Electrophoresis (2D-DIGE). Separate 2D-DIGE experiments were carried out for the individual comparisons of CON+NoRAC vs. ZN+RAC (Exp 1; n = 4 per treatment) to evaluate the effect of both RAC and ZnAA supplementation and CON+RAC vs. ZN+RAC (Exp 2; n = 4 per treatment) to evaluate the effect of ZnAA supplementation within RH-fed steers. Proteins were selected based on relative abundance and were identified using mass spectrometry. In Exp 1, abundance of isoforms of pyruvate kinase was decreased 20-25% (P ≤ 0.04) in ZN+RAC, relative to CON+NoRAC steers. Phosphoglucomutase-1 abundance was decreased by 63% (P < 0.0001), phosphoglycerate mutase-2 was decreased by 21% (P = 0.02) and glyceraldehyde 3-phosphate dehydrogenase tended to be increased by 71% (P = 0.06) in ZN+RAC steers, relative to CON+NoRAC. In Exp 2, phosphoglucomutase-1 abundance tended to be decreased by 60% (P = 0.09) and phosphoglycerate mutase-2 tended to be decreased 21% (P= 0.06) in ZN+RAC steers relative to CON+RAC steers. Decreases in phosphoglucomutase-1 and phosphoglycerate mutase-2 abundance in both experiments suggest these may be effects elicited by ZnAA supplementation. Changes in abundance of pyruvate kinase and glyceraldehyde 3-phosphate dehydrogenase were found only in the CON+NoRAC vs ZN+RAC comparison, and might be elicited by RH supplementation. These differences indicate that ZnAA and RH supplementation alter the protein abundance of enzymes involved in carbohydrate metabolism in skeletal muscle.

Keywords: ractopamine hydrochloride, zinc, 2D-DIGE