Effect of growth-promoting technologies on the proteome of bovine Longissimus lumborum

Abstract Text: The objective of this study was to identify the extent to which the protein profile of bovine Longissimus lumborum (LL) muscle in beef cattle is influenced by growth promoting technologies (GP) during the finishing period. Crossbred heifers (n = 66) from two harvest groups were fed a conventional feedlot diet, blocked by BW, and randomly assigned to 1 of 3 treatments: no GP (CON, n = 22); implant, no ractopamine hydrochloride (IMP, n = 22); and implant and ractopamine hydrochloride (COMBO, n = 22). Heifers assigned to the IMP treatment were administered an implant containing 200 mg trenbolone acetate and 20 mg estradiol on d 0 of the study, and the COMBO group received the same implant protocol as the IMP group, in addition to being fed 400 mg·d^-1·heifer ^-1 of ractopamine hydrochloride for the final 28 d before harvest. Heifers were harvested on d 90 of feeding, and a section of the LL was removed (n = 66) 1 h post mortem, placed on dry ice, and stored at -80°C. A subset (n = 6) from each treatment from the first harvest group was randomly selected for proteome analysis by two-dimensional difference in-gel electrophoresis (2D DIGE) coupled with mass spectrometry (MS) to identify proteins of interest. Peptide identifications with > 95% probability with at least 2 identified unique peptides were accepted. Twenty-five spots selected in the sarcoplasmic fraction corresponding to 21 proteins differed in relative abundance among growth promoting programs. Nine spots from the myofibrillar fraction corresponding to 6 proteins were also identified to be different among treatment groups. Increased abundance (P < 0.05) of identified proteins in sarcoplasmic and myofibrillar fractions of the LL muscle from heifers subjected to the COMBO treatment when compared with the LL from CON included metabolic enzymes (creatine kinase M-type, triosephosphate isomerase, beta-enolase), oxidative resistant proteins (peroxiredoxin-6, peroxiredoxin-2, protein deglycase DJ-1), muscle recovery proteins (myosin binding protein H, eukaryotic translation initiation factor 5A-1), and chaperone proteins (heat shock 70 kDa protein 1A). The results demonstrate that growth promoting technologies alter the protein profile of bovine muscle and suggest several metabolic pathways that are influenced by management practices that use these technologies. These pathways include metabolic processes, oxidative stress, and apoptosis cascades that can have an impact on growth efficiencies and meat quality in beef cattle.

Keywords: Bovine, Muscle, Proteome