Muscle fibre types in Iberian pigs:: influence of crossbreeding with Duroc breed and rearing conditions

The effect of rearing conditions (outdoors on pasture vs indoors on concentrated feed) and crossbreeding (pure Iberian vs 50 % Iberian x Duroc-Jersey) on fibre type proportions and diameters of muscles Biceps femoris (BF), Semimembranosus (SM) and Tibialis cranealis (TC) was studied. The major fibre types identified were type I, IIA, and IIB. The proportion of oxidative fibres (type I and IIA) found was higher than the one described in the literature for selected pig breeds. Type IIB fibres showed the greatest diameters (P < 0.05). The muscle was the factor with a higher influence on fibre proportions, the TC showing the higher proportion of type I and IIA fibres (P < 0.001). This was most likely due to the anatomical location and physical function of the studied muscles in the live animal. Rearing the animals outdoors produced a slight increase in the percentage of type I fibres, although it was not significant in any of the studied muscles (P > 0.05). The crossbreed only influenced type IIA and IIB fibres diameter in the SIM. ((C) Elsevier / Inra).