Interactive effects of zilpaterol hydrochloride and gender on carcass characteristics, post-mortem tenderness, and immunohistochemical analysis of longissimus muscle

Date

2015-12

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Abstract

The objectives of the current study were to evaluate the interactive effects of zilpaterol hydrochloride (ZH) and gender on carcass characteristics, post-mortem tenderness, and immunohistochemical analysis of the longissimus muscle (LM) in beef cattle. Steers and heifers (n=96) were sourced from a commercial feedlot and transported to the Texas Tech University Beef Center. Cattle were weighed and scanned using real-time ultrasound. Resulting data were used to predict empty body fat percentage. Steers (n=48; BW = 520 ± 30.4 kg; pEBF % = 26.2 ± 1.9) and heifers (n=48; BW = 466 ± 29.5 kg; pEBF % = 26.7 ± 1.7) were blocked within gender by pEBF % in a complete randomized block design and randomly assigned to pen (2 pens/block; 4 hd/pen) and treatment (6 pens/treatment): 1) control heifers (HC), 2) ZH heifers (HZ), 3) control steers (SC), and 4) ZH steers (SZ). A subset of cattle (n=45) were selected for selection of full strip loins and assigned an aging period (7, 14, 21, and 28 d postmortem). Steaks were cooked and analyzed for sliced shear force (SSF) and Warner-Bratzler shear force (WBSF) analysis. LM samples were subjected to RNA isolation, real-time quantitative PCR, and immunohistochemical analysis. No treatment x gender interactions were detected for any carcass variable measured (P ≥ 0.39). Dressing percentage was increased by 1.32 percentage units in ZH treated cattle relative to control (P = 0.01). ZH feeding increased the percentage of protein detected in the LM (P = 0.04). No significant treatment X gender interaction was detected for any shear force variable (P ≤ 0.07). ZH significantly increased the WBSF of steaks on d 7 (P ≤ 0.01), d 14 (P ≤ 0.01), d 21 (P = 0.01), but no difference in WBSF and control treatments were detected by d 28 (P = 0.17). A treatment x gender interaction (P = 0.02) was detected for the density of 2AR, so that ZH reduced the density of the receptor to a greater degree in heifers as opposed to steers. Feeding ZH affected all of the AR receptor subtypes evaluated. No differences in satellite cell distribution or nuclei density were detected. Treatment x gender interactions (P ≤ 0.01) were detected for fiber type % of MHC-IIX and fiber cross-sectional area of all 3 myosin isoform subtypes. No differences in gene expression of myosin isoform subtypes were presented. Our results indicate few interactive effects can be attributed to sex when evaluating ZH responses.

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Keywords

Cattle, Zipaterol hydrochloride, Beta-adrenergic receptor agonist

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