Occurrence of giant myofibres according to muscle type, pre- or post-rigor state and genetic background in turkeys

Forty-five male turkeys were bred to 15 weeks of age. At this age, the birds weighed 4, 6 and 8 kg depending on their genetic origin. At 3 min and 24 h post mortem samples from the pectoralis major (PM) and iliotibialis lateralis (ITL) muscles were excised for biochemical and histochemical measurements. At 3 min post mortem, except in the size of the myofibres, no differences in types, shapes or luminance due to glycogen was seen between the three lines in the respective muscles. Birds from the fast growing line had bigger muscle fibres than the two other lines, but the muscles did not present more glycolytic or oxidative enzyme activities. No muscle abnormalities were noticed at this stage. At 24 h post mortem, the presence of giant fibres (GF) was seen which differed proportions according to muscle and in genetic background. The GF were found both in the fast (PM) or mixed type (ITL) muscles. In this latter muscle they were more prevalent in the slow contracting muscle fibres than the other fiber types. It was concluded that the occurrence of the GF is independent of the genetic background of the birds or the type of muscle, but is dependent on the biochemical events occurring during rigor mortis.