Effects of simultaneous gestation and lactation in rabbit does on muscular characteristics of the youngs.

The aim of the experiment was to determine the influence of concurrent gestation and lactation in rabbit does on the post-natal growth and muscular characteristics of the progeny. Myosin heavy chain (MHC) isoform proportion, myofibrillar protein content and size of the myofibres were determined on day 29 or day 70 in the semitendinosus muscle of young rabbits born from either simultaneously pregnant and lactating does (PL group) or from only pregnant does (P group). There were no significant differences in the weight of the young rabbits of the two groups throughout the post-natal period, despite a non-significant reduction of birth weight by 9% in the PL group. On day 29, the proportion of perinatal MHC was higher (5.8% vs 2.3%) and that of the type-II isoforms was lower (91.5% vs 95.0%) in the PL group than in the P group (P < 0.01). The simultaneous gestation and lactation affected the maturation of secondary fibres. On day 70, the proportion of the MHC isoforms was similar in the two groups. These results suggest that concurrent gestation and lactation delayed the myofibrillar maturation rate.