A total of 144 pigs were used to study the effects of sex (barrows or gilts) and terminal sire line (Iberian or three genetic lines of Duroc: Duroc 1, Duroc 2 and Duroc 3) on performance and carcass and meat quality traits. Gilts showed slightly lower average daily gain, shoulder weight and trimming losses, but slightly better primal cuts yields and higher loin weight, while there was no significant effect of sex on meat quality traits or on the fatty acid composition of lard and muscle. There were important differences in performance and in carcass and primal cuts quality traits between pure Iberian pigs and all Iberian × Duroc crossbreeds evaluated, partly due to the lower slaughter weights reached by the formers. The different sire lines showed differences in several traits; Duroc 1 group showed lower backfat thickness and ham and shoulder trimming losses, and higher primal cut yields than Duroc 2 and Duroc 3 groups. Intramuscular fat (IMF) content remained unaffected by crossbreeding, but meat color resulted more intense and redder in crosses from the Duroc 1 sire line. The accumulation of fatty acids in lard was not affected by Duroc sire line, while animals of the group Duroc 2 showed higher levels of monounsaturated fatty acid and lower of polyunsaturated ones in IMF. These results highlight the importance of considering not only performance, but also carcass and meat quality traits when deciding the Duroc sire line for crossbreeding in Iberian pig production.

The effects of pig crossbreeding (Iberian versus Iberian x Duroc 50%) and rearing conditions (out doors versus indoors) on muscle fiber composition, myoglobin content and objective muscle color in biceps femoris and tibialis crancalis muscles have been studied. Muscle fibers were identified as types I, IIA, IIB, oxidative IIB and IIC and the proportion of each fiber type was determined by a computer ized image analysis. Color co-ordinates L*, a*, and b* were measured and both chroma (C*) and hue angle (h°) were calculated. Myoglobin content and chroma value were significantly higher in tibialis cranealis muscle than in biceps femoris muscle (p ≤ 0.001), whereas the former muscle showed the lowest lightness and hue angle values (p ≤ 0.001). Moreover,tibialis cranealis muscle exhibited a higher total proportion of oxidative fibers, types I, IIA and IIBx (p ≤ 0.05), and a lower fat content than did biceps femoris muscle (p ≤ 0.001). The muscles of pigs reared outdoors tended to show a higher per centage of oxidative fibers (type I) than did muscles from indoor reared pigs, although not to a sig nificant extent. Rearing conditions significantly affected color, muscles from outdoor reared pigs ex hibiting higher lightness (L*), chroma (C*) and hue angle (h°) than muscles from indoor reared pigs. However, neither the crossbreeding nor the rearing conditions showed a significant influence on myoglobin concentration of muscles.

Two production systems and several ages at slaughter were used: 12, 14 and 16 months for outdoor rearing (with the final finishing phase in the Montanera system, in which fed was based on natural resources, mainly acorns and grass) and 8, 10 and 12 months for animals reared indoors (intensive system: with feed based on commercial fodder) to evaluate their effect on the muscle fibre population and size of the Longissimus thoracis, (LT) muscle, as well as fresh loin quality traits. Animals that were older at slaughter revealed increased fibre sizes of the LT muscles in the pigs reared in the Montanera system. The LT muscles of the animals reared in intensive systems had a lower percentage of type I fibres and higher size of type IIB than those reared in the Montanera system. The approximate composition and instrumental colour of Montanera fresh loins were affected by the animal slaughter age. In the case of the intensive system, the effect of animal slaughter age had an impact on the approximate composition, instrumental colour, water loss and textural properties. Therefore, different ages at slaughter of Iberian pigs showed variations in some quality parameters in the fresh loins in both the Montanera and Intensive systems, thus proving to be a factor of variability and homogeneity of the Iberian products. The meat from Iberian pigs reared in an intensive system and slaughtered at a younger age proved to be more tender. The production system affected all the above quality traits, with the exception of water loss.