initiation (Barb et al., 1997).It was apparentlyfound that some metabolic hormones were closelyrelated to backfat and puberty attainment (Booth et al.,1994; Rozeboom et al., 1995). In numerousdomesticated species, leptin and insulin-like growthfactor-I (IGF-I) have been recognized as the regulatorsof cellular growth and differentiation, onset of puberty,and body composition (Bidanel et al., 1996)