Effects of recombinant bovine somatotropin on performance and biological activity of skeletal muscle over the finishing phase of feedlot heifers

Abstract Text: Our objective was to determine if recombinant bovine somatotropin (rBST) enhanced performance and biological activity in skeletal muscle over the finishing phase of feedlot heifers.  Heifers (n = 16; initial BW = 457 ± 3 kg) were randomly assigned to pens (4 pens/treatment; 2 head/pen) and treatment: 1) no rBST (control); 2) 500 mg/hd of sometribove zinc at d 0 and 14 (rBST; Posilac^®; Elanco Animal Health).  Upon arrival, heifers were acclimated for 14 d.  Longissimus muscle biopsies for gene expression and protein abundance were performed on d 0, 14, 28, 42 and 56.  On d 88 (102 DOF) heifers were harvested and carcass data were collected.  Average daily gain, DMI and G:F were not affected by treatment (P > 0.05).  There was no change in final BW, HCW or DP (P > 0.05); however, there was a tendency for control cattle to have greater marbling and decreased KPH (P ≤ 0.08).  Loin muscle area, fat thickness, and yield grade did not differ (P > 0.05).   Using RT-QPCR, genes of interest: AMPKα, β₁AR, β₂AR, β₃AR, MHC-I, MHC-IIA, MHC-IIX, IGF-I, GPR43, GPR41, Glut4, SCD, CEBPβ, and PPARγ were quantified.  The rBST cattle had the greatest quantity of AMPKα mRNA (P < 0.05) on d 0.  There was a day effect on MHC-IIA, MHC-IIX, β₂AR, PPARγ and SCD (P < 0.05).  All cattle had the greatest concentration of MHC-IIA mRNA on d 56 and the greatest concentration of MHC-IIX mRNA on d 14, 28, and 42 (P < 0.05).  Concentration of β₂AR mRNA were the greatest on d 56 (P < 0.05), while the greatest concentration of PPARγ and SCD mRNA were on d 0 and 56 (P < 0.05).  No differences (P > 0.05) were observed in mRNA between treatments for MHC-I, β₃AR, GPR41 or Glut4.  Protein quantification was performed utilizing western blotting procedures to assess the abundance of β₁AR, β₂AR and β₃AR.  There was a day effect on protein abundance (P < 0.05).  The βAR were quantified at their greatest abundance on d0 for β₁AR, d 0 and 42 for β₂AR, and d 0 and 28 for β₃AR (P < 0.05).  These data indicate that as DOF increase, the effects of skeletal muscle biological activity may not be solely dependent on rBST administration.  However, further investigation is needed to elucidate interactions that effect muscle metabolism during the finishing period.

Keywords: β-adrenergic receptor, myosin heavy chain, recombinant bovine somatotropin