Effect of Zinc Amino Acid Complex and Ractopamine on Skeletal Muscle Gene and Protein Expression
A study was conducted to evaluate the effect of 50 ppm supplemental Zn amino acid complex (Availa Zinc®, AZ) and ractopamine (RAC) on the growth performance, carcass composition, blood metabolites, and muscle gene and protein expression in finishing gilts. Twenty-four crossbred gilts were individually housed, blocked by ancestry and BW (108.5 ± 1.7 kg) into 6 blocks and assigned to 1 of 4 dietary treatments: A) Control (50 ppm Zn from ZnO), B) A + RAC, C) A + 50 ppm AZ, and D) B + 50 ppm AZ. The Control diet was formulated to 1.10% TID Lys. RAC was fed at 5 ppm from d 0 to 7 and 10 ppm from d 7 to 14. Individual BW and feed disappearance were evaluated on d 0, 7 and 14. Longissimus dorsi (LD) and semimembranosis (SMB) muscle samples were collected immediately after exsanguination for analysis of myosin heavy chain (MyHC) gene expression and phosphorylation (p-) state of AKT, S-6, and 4E-BP1 proteins. Expression of MyHC I, IIa, IIx and IIb were quantified using real time PCR; p-AKT, p-S6 and p-4E-BP1 were determined using western blot technique. Growth and carcass data were analyzed using the GLM procedure of SAS and data for protein and gene expression were analyzed using the mixed procedure. RAC increased (P < 0.01) d 0 -14 ADG (25.7%), G:F (20.5%), LEA (10%) and tended (P < 0.08) to increase primal ham weight. RAC decreased expression of MyHC IIa in the LD (P < 0.01) and SMB (P < 0.03) and increased (P < 0.05) expression of MyHC IIb in the LD. Feeding AZ alone tended to decrease expression of IIx in the LD, however IIx expression tended to increase (P < 0.07) when AZ was fed with RAC. Both RAC and AZ increased (P < 0.05) p-AKT in the LD. Feeding RAC or AZ, but not RAC + AZ, tended to increase p-4E-BP1 (P < 0.07) in the LD. Feeding RAC + AZ tended (P<0.06) to increase p-4E-BP1 in the SMB. These data indicate that RAC induced hypertrophy may be regulated partially by AKT in swine. Feeding AZ appears to have influenced the phosphorylation state of proteins regulated by mTOR, though this did not result in a biologically measurable growth effect in this short-term study.
zinc, ractopamine, protein synthesis