Meat quality and fatty acid profile of M. longissimus dorsi of growing bulls under insulated, uninsulated and outdoor housing conditions

The objective of the present study was to compare the colour, chemical composition, meat quality and fatty acid profile of the longissimus dorsi (LD) muscle of growing bulls housed in an insulated tie-stall, an uninsulated barn or a forest paddock. Two housing experiments were conducted at the North Ostrobothnia Research Station of MTT Agrifood Research Finland in Ruukki (64 degrees 44'N, 25 degrees 15'E). The first experiment was conducted from November 1999 to October 2000 and comprised 30 Hereford bulls, the second from November 2000 to December 2001 with 30 Ayrshire bulls. In both experiments the bulls were divided into six groups of five animals according to live weight and the groups were randomly allotted to one of three treatments: tie-stall in an insulated barn (IB bulls, ten animals/individual stall), uninsulated barn (UB bulls, five animals/pen, two pens) and forest paddock (PAD bulls, five animals/paddock, two paddocks). Nine carcasses from experiment 1 (three/treatment) and twelve from experiment 2 (four/treatment) were randomly selected for meat quality analyses. After slaughter, the carcasses were cooled for 24h at 2 degrees C and LD samples were taken by complete cross-section between the 12th and 13th ribs. The results were calculated across the two experiments and analysed as one data. There were no differences between housing environments in temperature or pH of the LD or meat moisture, fat or protein composition of the LD. Instead, the myoglobin content of the LD was 21% higher in PAD bulls than in IB bulls (p < 0.05). Between IB and UB bulls there was no difference in meat myoglobin content and there were no significant (p < 0.05) differences between housing environments in the colour of the LD. However, the muscle tended to be 6% lighter (L-value) in IB bulls than in PAD bulls (p = 0.09). There were no significant differences in shear force or sensory analysis (tenderness, juiciness, overall flavour) between treatments. The LD of the PAD bulls contained a higher proportion of 18: 2 and 18: 3 fatty acids compared to that of IB bulls (p < 0.05). There were no significant differences in the saturated fatty acid (SFA) or monounsaturated fatty acid proportions of the LD between treatments. Instead, the polyunsaturated fatty acid (PUFA) proportion of the LD was 34% higher in PAD bulls than in IB bulls (p < 0.05). The PUFA: SFA ratio was higher in PAD bulls than in IB bulls (p < 0.05) but there was no difference in the PUFA: SFA ratio between UB and IB bulls. In conclusion, there were no important effects of housing system on the meat quality characteristics of the LD, although according to meat fatty acid profiles, outdoor housed bulls produced meat with a higher PUFA: SFA ratio than tethered bulls in an insulated barn.