223 The effects of supplemental zinc and ractopamine hydrochloride on the Longissimus dorsi proteome of finishing beef steers

Abstract

Abstract The objective of this study was to determine how steer growth rate and Zn nutrition affects the muscle proteome. Forty-eight, high percentage Angus steers (494 ± 18.2 kg) were blocked by BW and GeneMax gain score (GeneMax Focus, Zoetis, Parsippany, NJ) to treatments arranged in a 2×2 factorial. On d 0, steers were assigned to control (CON; 36 mg Zn/kg dry matter [DM]) or supranutritional Zn (SUPZN; CON + 60 mg Zn/kg DM as ZnSO4+ 60 mg Zn/kg DM as Zn-amino acid complex) dietary treatment (ZNTRT), and housed in pens (n = 6 or 8 steers/pen) with Growsafe bunks. On d 62, within ZNTRT steers were assigned to ractopamine hydrochloride treatments (RACTRT) of 0 (NO) or 300 mg·steer-1·d-1(RAC) for 28 d. Longissimus dorsi biopsies (between 12thand 13thrib) were collected on d 77. Sarcoplasmic fractions were extracted and submitted for proteomics analysis using mass spectrometry (LC-MS/MS). Data were log transformed and comparisons made using t-tests with adjusted P-value cutoffs of 0.1. Differences were noted in abundance of proteins involved in glycolytic, retinol and fatty acid metabolism. A shift from slow to fast muscle fiber type was suggested by decreased abundance of myoglobin and slow skeletal troponin 1 in steers fed RAC compared to steers not fed RAC within CON (P ≤ 0.04), while these proteins also tended to be lesser due to SUPZN within steers not fed RAC (P ≤0.09). The intermediate filament associated protein, vimentin, tended to be less abundant in RAC steers (P ≤ 0.09), suggesting RAC affects cellular remodeling. Proteins involved in immune function were also affected; for instance, the acute phase protein alpha-1-acid glycoprotein was more abundant in CON-RAC compared to either SUPZN-RAC (P = 0.001) or CON-NO (P = 0.02). Ractopamine hydrochloride and supranutritional Zn, independently and collectively, affect proteins involved in muscle metabolism, cellular remodeling and immune function in beef steers.