The Crossroads between Zinc and Steroidal Implant-Induced Growth of Beef Cattle

Abstract

Growth-promoting technologies such as steroidal implants have been utilized in the beef industry for over 60 years and remain an indispensable tool for improving economic returns through consistently improved average daily gain via increased skeletal muscle hypertrophy. Zinc has been implicated in skeletal muscle growth through protein synthesis, satellite cell function, and many other growth processes. Therefore, the objective of this review was to present the available literature linking Zn to steroidal implant-induced protein synthesis and other metabolic processes. Herein, steroidal implants and their mode of action, the biological importance of Zn, and several connections between steroidal implants and Zn related to growth processes are discussed. These include the influence of Zn on hormone receptor signaling, circulating insulin-like growth factor-1 concentrations, glucose metabolism, protein synthesis via mTOR, and satellite cell proliferation and differentiation. Supplemental Zn has also been implicated in improved growth rates of cattle utilizing growth-promoting technologies, and steroidal implants appear to alter liver and circulating Zn concentrations. Therefore, this review provides evidence of the role of Zn in steroidal implant-induced growth yet reveals gaps in the current knowledge base related to optimizing Zn supplementation strategies to best capture growth performance improvements offered through steroidal implants.

Keywords: cattle; estradiol; growth; hormones; trace minerals; trenbolone acetate; zinc.

Figure 1

Proposed physiological pathway interactions of combination E₂ + TBA steroidal implants and Zn in skeletal muscle cells as discussed in this review. Specific focus is placed on the genomic and non-genomic steroid hormone pathways, protein and DNA synthesis pathway, and the corresponding points at which evidence suggests Zn interacts with these pathways. Definitions: AKT (Protein kinase B), Androgen GPR (Androgen specific G protein-coupled receptor), E₂ (Estradiol), EGFR (Epidermal growth factor receptor), ERK (Extracellular signal-regulated kinase), GPER-1 (G protein-coupled estrogen receptor 1), hbEGF (Heparin binding epidermal growth factor-like growth factor), IGF-1 (Insulin-like growth factor 1), IGF1R (Insulin-like growth factor 1 receptor), IRS (Insulin receptor substrate), MMP2/9 (Matrix metalloproteinase 2/9), mTOR (Mammalian target of rapamycin), mTORC1 (Mammalian target of rapamycin 1), mTORC2 (Mammalian target of rapamycin 2), PDK1 (Phosphoinositide-dependent kinase-1), PI3K (Phosphoinositide 3-kinases), RAS (Ras family of related GTPase proteins), SR (Sarcoplasmic reticulum), TBA (Trenbolone acetate), ZIP7 (Zinc transporter SLC39a7), ZIP8 (Zinc transporter SLC39a8), ZIP14 (Zinc transport SLC39a14).