PSXII-13 A proteomics characterization of the effects of growth-promoting technologies on muscle metabolism and carcass traits in Angus Steers.

Abstract The objective of this study was to investigate the skeletal muscle proteome of Angus (Bos taurus) steers managed with and without the use of growth-promoting technologies (GPT). Therefore, 10 Angus (n = 5/treatment) steers with a similar initial shrunk body weight of 338 kg were randomly assigned to: Treatment (TRT) cattle received a hormonal in-ear implant on d 0 (100 mg trenbolone acetate/14 mg estradiol benzoate) and on d 84 (200 mg trenbolone acetate/28 mg estradiol benzoate). The TRT group received however an in-feed ionophore (35 g/ton DM basis; Monensin), antibiotic (7 g/ton DM basis; Tylosin), and β-agonist during the last 42d of the feeding period (27 g/ton DM basis; Ractopamine hydrochloride), allowing for a 2d withdrawal period before harvest. And The Control (CON) cattle did not receive any of the above-listed GPTs. All cattle were fed a steam-corn finishing feedlot diet for 180 days on feed. Steers in the TRT group had greater final shrunk body weight (679 vs. 622 kg), hot carcass weight (416 vs. 393 kg), and Longissimus muscle area (90.7 vs. 87.1 cm²) compared to the CON animals. For the purpose of this study and at around 4 h post-slaughter, Longissimus thoracis (LT) were collected and stored in an ultrafreezer (-80 °C) for shotgun proteomics analysis using LC-MS/MS. The supernatants of the total protein extracts were washed with acetone and the resulting pellets were sonicated before protein quantification using the Pierce BCA Protein Assay Kit. After digestion of the proteins using the EasyPep Mini MS Sample Prep Kit, the peptides were subsequently analysed by LC-MS/MS to identify and quantify the proteins using the Bos taurus database. First, volcano plots (fold change of 1.5 and P-value < 0.05) allowed to identify the differentially abundant proteins (DAPs). 87 DAPs were more abundant in TRT and 27 were in the CON group. Steers submitted to TRT had a greater DAPs related to cellular energy metabolism (NDUFS, NDUFB, HSPB, HSPA9), while CON animals had a DAPs associated with catabolic processes (FKBP4, NPM1, GALM, USP15) and oxidative stress (MAPK1, NPM1, PEBP1, LMO7, MAP1LC3B). The DAPs in the TRT cattle compared to CON cattle are directly related to more efficient cellular metabolism, favoring muscle mass growth and deposition. The CON group presented greater DAPs associated with muscle degradation, autophagy and oxidative stress, which explains the poorer growth performance compared to TRT cattle. The in-depth analysis using Partial Least Square Discriminant analysis (PLS-DA) clearly separated the two cattle groups and allows proposing several biomarkers that mostly emanate from the cellular respiration. The study demonstrates that GPT enhance muscle metabolism by activating anabolic pathways. Therefore, changes in cellular respiration pathway leads to improved growth performance and carcass traits in Angus steers.