Effect of breed type and residual feed intake on meat and collagen quality and expression of genes involved in collagen synthesis and degradation in bovine m. gluteus medius

Abstract

Residual feed intake (RFI) is an index of feed efficiency that has been demonstrated to be moderately heritable, with cattle having low RFI values being efficient as they consume less feed for the same weight gain. This may be of financial benefit to producers, but to be fully beneficial to producers selection for low RFI should not compromise meat quality. One of the most important characteristics of meat quality is tenderness, for which the consumer is willing to pay a premium. The m. gluteus medius (top sirloin) is known to be moderate tough, but with post mortem ageing this muscle may have reduced toughness and may then be marketed as a tender muscle which will add value to the beef carcass. Collagen is known to be involved in determining the ultimate or background toughness of meat and this may be affected by cattle breed, feed efficiency (selection for RFI), and post-mortem ageing. Seventy-one (71) steers from three different breeds (Angus n=23, Charolais n=24, and Kinsella Composite n=24) were used to investigate the interaction between RFI and cattle breed type on meat quality and intramuscular collagen characteristics of the m. gluteus medius after 3 and 13 days of post mortem ageing. The results indicated that RFI did not affect meat pH, drip loss, sarcomere length and Warner-Bratzler shear force, but intramuscular collagen heat solubility was highest in efficient steers (low RFI), indicating that background toughness was reduced in low RFI steers. Intramuscular collagen heat solubility also increased with post mortem ageing, while cooked beef toughness as measured by Warner-Bratzler shear force decreased. From the 71 steers in this study, 12 steers from each breed type (total n=36) were selected for high (n=6) and low (n=6) collagen solubility. Intramuscular RNA was isolated from the m. gluteus medius and the relative level of expression of 38 genes reported to be involved in collagen synthesis and degradation were determined and related to meat quality and collagen characteristics. Gene expression analysis indicated that genes involved in collagen biosynthesis and degradation were unrelated to heat collagen solubility. The relative expressions of LOX, FGFR1, FGF2, and SMAD6 were lower for muscles of Angus than of Charolais or Kinsella crossbred steers, while expressions of TIMP3 and ITGA1 were highest in Angus and Kinsella crossbred steers, and AKT1 was highest in Angus steers. These results indicated that beef producers can use this feed efficiency index to select for low RFI cattle without compromising meat quality and that the toughness of the gluteus medius and the contribution of collagen to it can be decreased with 13 days post mortem ageing. Gene expression levels may reflect differences in intramuscular adipose and collagen development between the breed types but further investigation is warranted to test this hypothesis.