Intersections of animal production practices on meat quality, intramuscular collagen and expression of genes related to collagen and myofibrillar synthesis and degradation

Abstract: Beef quality, particularly tenderness, continues to be a major challenge in the beef industry resulting in significant economic losses. Beef tenderness is influenced by genetic factors, especially the expression of genes associated with collagen and collagen crosslink synthesis, live production factors such as management, including growth promotant (GP) utilization, and post-mortem factors such as ageing, processing and packaging. Residual feed intake (RFI) is a measure of feed efficiency and has the potential to increase profitability in the beef industry and reduce green house gas emissions. In this thesis research, our overall aim was to elucidate the effects of RFI and GPs, and their interactions, on growth performance and meat quality of crossbred Angus steers, and the expression of genes associated with collagen and collagen crosslink synthesis. This was achieved by testing different hypotheses in three experimental studies. A total of 48 crossbred Angus steers classified as low (n = 27) and high (n = 21) RFI status were randomly allocated into steroid (n = 12), beta-agonist (n = 12), combined steroid implant and beta-agonist (n = 12), and control treatments (n = 12). The first study showed an important interaction between RFI and steroid implant to enhance feed conversion efficiency and average daily gain (ADG). The use of steroid implants increased body weight at the end of the treatment phase, although it did not influence the concentration of circulating insulin-like growth factor 1 (IGF-1). Cooked steaks of the semimembranosus (SM) muscle from low RFI steers were tougher than those from high RFI steers, as were steaks from both gluteus medius (GM) and SM muscles obtained from implanted steers compared to those from non-implanted steers. Post-mortem ageing was found to have the most significant effect on meat quality characteristics, particularly on tenderness as steaks from both muscles aged for 12 days were more tender compared to steaks aged for 3 days. In the second study, we explored the effect of RFI and GPs on the total collagen content of both SM and GM muscles, and the density of two trivalent crosslinks, Ehrlich’s chromogen (EC) and pyridinoline (PYR), of the SM muscle. In the SM muscle, insoluble collagen content was influenced by an interaction between RFI, steroid implant and ageing period where it was higher in muscles from steers of low RFI status that were implanted and aged for 3 days than in muscles aged for 12 days. Insoluble collagen content in the GM muscle was lower in muscles from implanted steers than in non-implanted steers. Percentage solubility in the SM muscle increased in muscles from low RFI steers non-supplemented with beta-agonist and aged for 12 days rather than 3 days, while percentage solubility in the GM muscle was higher in muscles aged for 12 days than for 3 days. The intramuscular connective tissue (IMCT) structure was found to be weakened with post-mortem ageing as soluble collagen concentration increased by day 12 in both muscles. While beta-agonist increased the density of both mature crosslinks in the SM muscle, steroid implants decreased EC density but increased PYR density. The expression of 31 genes associated with collagen and collagen crosslink synthesis, and myofibril degradation were profiled in the third study using quantitative real time polymerase chain reaction. Results showed a lower expression level of CAPNI in muscles from low RFI steers treated with steroid implants and ractopamine hydrochloride (RH), than high RFI steers treated with both GPs. The expression of the CAST gene was tentatively higher in muscles from low RFI steers, hence the toughness of steaks of SM muscles from low RFI steers, supported by the tendency for MMP13 to have low expression in SM muscles from low RFI steers. Steroid implant did not increase the expression levels of collagen synthesising genes COL1A1, COL3A1, ITGA11, ITGB1, TIMP1, TIMP2, and FN1. Results from this PhD research thesis contribute to knowledge on selection for improved RFI and its effect on live production and meat quality characteristics, and the advantages and disadvantages of the use of GPs individually and in combination on live production and meat quality characteristics, and on the expression of target genes.