Fibre types in Longissimus dorsi from wild and highly selected pig breeds.

Longissimus dorsi muscles from six pig breeds were examined histologically. It was found that mean fibre diameter increased with degree of selection in domestic pigs and that the percentage of red fibres decreased-i.e. from Mangulica and Black Slavonian to Large White and Swedish Landrace. The percentage of white fibres showed the reverse tendency whilst that of the intermediate type was not markedly changed. In semi-wild pigs, the percentage of red fibres was still higher and in forest pigs there were neither white nor intermediate fibres in longissimus dorsi. Beneath the sarcolemna of red fibres there was a significantly higher number of mitochondria than in the central parts of the fibre. The distribution of the 'giant fibres' indicated that this formation may be found in the muscles of both stress-susceptible and stress-insusceptible pigs.