8:00 am - 9:00 am
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Patience Coleman. This seminar is open to the general public to attend.
Meeting ID: 943 5495 8561
Thesis Topic: Intersections of animal production practices on meat quality, intramuscular collagen and expression of genes related to collagen and myofibrillar synthesis and degradation
PhD with Dr. Heather Bruce.
Beef quality, particularly tenderness, continues to be a major challenge in the beef industry resulting in significant economic losses. It is influenced by genetic factors, especially the expression of genes associated with collagen and collagen crosslink synthesis, production factors such growth promotant (GP) utilization, and post-mortem factors such as ageing. Residual feed intake (RFI) is a measure of feed efficiency and has the potential to increase profitability in the beef industry. The overall aim of this thesis was to elucidate the effects RFI and GPs, and their interactions, on live performance and meat quality of crossbred Angus steers, and the expression of genes associated with collagen and collagen crosslink synthesis.
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 that the use of steroid implants enhanced feed efficiency, which was reflected in the higher average daily gain (ADG) of implanted steers compared to non-implanted steers. 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). Most importantly, RFI interacted with steroid implant to enhance feed efficiency and ADG. 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 for 12 days increased beef tenderness of steaks from both muscles.
The second study explored the effect of RFI and GPs on the total collagen content of both SM and GM muscles, and the density of Ehrlich’s chromogen (EC) and pyridinoline (PYR) crosslinks 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 low RFI steers 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 solubilty in the SM muscle increased in muscles from low RFI steers unsupplemented 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. 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 beta-agonist, than high RFI steers treated with both GPs. The CAST gene was revealed to have the potential to be highly expressed 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. This thesis contributes to knowledge on selection for improved RFI, the advantages and disadvantages of the use of GPs individually and in combination, and their effect on live production and meat quality characteristics, and also through the expression of target genes.