Information on clone offspring F1 is limited, especially in species with a long inter-generation interval such as cattle. As cloned cattle exhibit a slight delay in muscle maturation until puberty (Jurie et al. 2009 Animal 3, 244-250), the present study aimed to investigate the contractile and metabolic muscle characteristics of F1 at 8, 12, and 18 months of age. Repeated biopsies of the semitendinosus muscle were collected on 10 F1 heifers born after AI of cloned cows at the experimental farm of INRA. Muscle characteristics of these offspring were compared with those of 9 female clones and 8 AI control heifers previously biopsied at the same ages. All animals (clones, F1, and controls) were female Holstein, born and raised under the same conditions in the same farm. Biopsy samples were stored frozen at -80°C until analysis for contractile and metabolic characteristics. The type of contractile fibers was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH) and cytochrome-c oxidase (COX) activities (μmol min-1 per gram of muscle). Data were analyzed separately for each time of biopsy using the GLM procedure of SAS (SAS Institute, Cary, NC, USA). The statistical model contained the group as fixed effect. When a significant effect was detected, differences between least squares means were further separated by the PDIFF option of SAS. Comparison of contractile characteristics from the 3 groups of animals is presented in Table 1. The proportion of MyHC I (slow oxidative isoform) and MyHC IIx (fast glycolytic isoform) in the muscles of F1 was not significantly different from those of controls at 8 and 12 months of age. F1 had different muscle contractile properties compared with clones at 12 months of age. At 8 months of age, F1 had greater ICDH activity than controls (1.39 ± 0.22 v. 0.54 ± 0.007; P ≤ 0.002) and greater COX activities (11.4 ± 1.6 v. 4.2 ± 0.9; P ≤ 0.003), but this was not observed later on. Altogether, these data indicate that the muscles of F1 were more oxidative than those of controls. This was not related to a higher percentage of type I fibers but rather to a higher percentage of type IIA fibers. A delay in muscle maturation was only partially found in F1. Table 1.Contractile characteristics (mean ± SE) of the semitendinosus muscle from controls (n = 8), clones (n = 9) and clone offspring (F1, n = 10) heifers