The influence of grazing prior to finishing on a high concentrate ration, on the colour and sensory characteristics of muscle from early or late maturing bulls slaughtered at the same carcass weight

Objectives: Traditionally in Ireland, suckler bull production systems were based on late-maturing (LM) genotypes offered high concentrate rations post-weaning. Inclusion of a grazing period prior to a high concentrate ration would decrease the cost of production. A challenge in this system is to achieve the required carcass fat cover at a market-specific weight. Early-maturing (EM) genotypes may be more suited to this grass-based production system. The objective was to determine the impacts of variations in the traditional sucker bull production system on aspects of carcass and meat quality. Materials and Methods: Twenty eight Spring-born LM (mean birth weight March 8) and 28 Spring-born EM (mean birth date March 30) weaned bulls were assigned (December 1) to a 2 (breed type) x 2 (production system (PS)) factorial arrangement of treatments. The PS were: concentrates ad libitum together with grass silage until slaughter (HC) or grass silage ad libitum and 2 kg concentrate for 123 days, followed by pasture for 99 days and then concentrates ad libitum together with grass silage (GHC). Bulls were slaughtered in a commercial abattoir when the estimated carcass weight of the individual treatment groups was 380 kg. Post slaughter (48 hours), carcasses were cut at the 5/6 rib inter face and the pH of the longissimus muscle and the lightness (L), redness (a) and yellowness (b) of subcutaneous fat and muscle (after 1hour bloom) were recorded. A sample of cube roll (6/10 rib) was vacuum packaged and frozen for subsequent chemical analysis and the remainder was aged for 14 days (20 C) prior to analysis by a trained sensory panel. Data were subjected to analysis of variance using a model that had maturity and PS as main effects together with their interaction. Initial age was used as a covariate where appropriate. Results: Mean carcass weight (381 kg) was close to target and did not differ significantly between treatments. Mean age at slaughter was 15.0 and 18.3 months for LM bulls and 16.7 and 18.6 months for EM bulls in the HC and GHC system, respectively, resulting in a significant interaction (SED 0.35). Both maturity types had similar fat cover in the HC system but LM had less (P < 0.05) than EM in the GHC system. Carcass fat was more yellow (P < 0.05) for EM than LM. There was little difference between treatments in muscle pH but muscle from HC bulls had higher (P < 0.05) “L” and lower “a” values than muscle from GHC bulls. Intra-muscular lipid concentration was higher (P < 0.05) for EM compared to LM and for HC compared to GHC. There was no difference (P < 0.05) in scores for tenderness, juiciness, beef flavour, abnormal flavour or overall liking between muscle from LM and EM. Muscle from HC bulls had higher (P < 0.05) scores for tenderness, flavour liking and overall acceptability and lower (P < 0.05) scores for abnormal flavour compared to muscle from GHC bulls. Conclusion: Choosing EM rather than LM genotypes would increase the likelihood of achieving a fat cover specification at the carcass weight examined, but would have little impact on the meat quality attributes examined. The lower cost production system examined resulted in an alteration in muscle colour and sensory characteristics. It is unlikely however that the scale of the alterations observed is of relevance to the consumer. Keywords: Bulls, Maturity, Colour, Sensory characteristics