The Influence of Supplemental Zinc and Ractopamine Hydrochloride on the Performance and Longissimus Thoracis Proteome of Finishing Beef Steers

Abstract

To determine how Zn and ractopamine hydrochloride (RAC) supplementation affect the longissimus thoracis muscle proteome in beef cattle, 48 high percentage Angus steers (494±18.2 kg) were utilized in a 2×2 factorial study design. Steers were blocked by body weight (BW) and genetic gain potential (GeneMax; Zoetis, Parsippany, NJ) into control (CON; analyzed 36 mg Zn/kg dry matter [DM]) or supranutritional Zn (SUPZN; CON+60 mg Zn/kg DM from ZnSO4+60 mg Zn/kg DM from Zn-amino acid complex; Availa Zn, Zinpro, Eden Prairie, MN) dietary treatments (ZNTRT). Starting 28 d prior to harvest, steers were blocked by BW within ZNTRT to RAC treatments (RACTRT) of 0 (NO) or 300 mg·steer−1·d−1 (RAC; Actogain 45, Zoetis). After 15 d on RACTRT, longissimus thoracis biopsies were collected from all steers for proteomic analysis. Twenty-eight steers (n=7 per treatment) were harvested at a commercial abattoir on Day 90. A ZNTRT×RACTRT effect showed SUPZN-RAC steers had a greater dressing percentage than other treatments (P≤0.02). Steers fed SUPZN had a greater hot carcass weight, carcass-adjusted final BW, overall average daily gain, and overall gain to feed (P≤0.05). Differentially abundant proteins involved in energy metabolism, muscle structure, and protein synthesis potentially indicate muscle fiber characteristic differences because of Zn and RAC supplementation.Both myosin light chain kinase 2 and eukaryotic translation initiation factor 5A-1 were more abundant in SUPZN-RAC steers than SUPZN-NO (P≤0.05) or CON-NO (P≤0.04) steers when analyzed for phosphorylation modifications. L-lactate dehydrogenase B was more abundant in SUPZN-NO steers than CON-NO (P=0.03) or CON-RAC (P=0.01) steers. In conclusion, increased Zn supplementation may be needed to optimize the hypertrophic effects of RAC through its effects on the longissimus thoracis proteome.