Effect of some biological and zootechnical factors on appearance of giant fibres in the rabbit. Consequences on muscle fibre type, morphology and meat quality

Three experiments were carried out to investigate the contribution of some factors on the frequency of appearance and on histochemical and morphological traits of giant fibres (GF), and the effect of the GF presence on muscle fibre type and morphology and on meat quality. Experiment 1 tested the effect of the type of muscle (Biceps femoris - BF, Gastrocnemius medialis - GM, Soleus - SOL, Semimembranosus proprius - SMP, Longissimus lumborum - LL, Psoas major - PM). Experiment 2 considered the age at slaughter (5, 8 and 11 weeks) and feeding restriction (ad libitum: until 5 weeks of age, followed by slaughter; L-H: 70% ad libitum from 5 to 8 weeks of age, then 90% from 8 to 11 weeks; H-L: the opposite). Experiment 3 took into account the sire genetic origin (INRA9077, INRA3889, Hy+), the dietary energy concentration (H diet: 11.99 MJ DE/kg DM; L diet: 9.67 MJ DE/kg DM) and the age at slaughter (69, 74 or 84 days) at equal body weight (2.5 kg). On all muscles considered, GF were always classified into the 3 fibre types (W, R and R) even though one or more fibre types were not present into the normal fibres of a given muscle. The type of muscle influenced (P<0.001) the appearance of GF (BF>GM=SOL=SMP>LL>PM). The frequency of appearance of GF was reduced as age increased (P<0.05). Animals with GF exhibited the highest pHu ( BF: 5.83 vs 5.76, P<0.05), percentages (BF: 5.3 vs 3.6%, P<0.10) and cross-sectional area (LL: 1643 vs 1243m2, P<0.01) of R fibres. Increasing numbers of GF in BF muscle also led to an increase in percentage of R fibres (P<0.05), aldolase activity (P<0.01), and pHu (P<0.05).