Abstract.It has been shown in various species that the onset of puberty is closely associated with body growth and nutritional state rather than age. The present study was conducted to determine the timing of puberty and to clarify body growth and metabolic changes around the pubertal period in female Shiba goats. Blood samples were collected between 10 to 38 weeks of age from 12 female goats, and plasma concentrations of progesterone, metabolites (glucose, nonesterified fatty acid, ketone body and acetic acid) and metabolic hormones (insulin and insulin-like growth factor-I (IGF-I)) were analyzed. Physical parameters (body weight, withers height and body length) were also measured at the blood sampling. The week when plasma progesterone concentrations first exceeded 1.0 ng/ml was designated as the onset of puberty. The results showed that the average age of the onset of puberty was 27.0 ± 0.9 (mean ± SEM) weeks in female Shiba goats. When the goats reached puberty, the average values of body weight and goat body mass index ((body weight (kg)/withers height (cm)/body length (cm)) × 10 3 ) were 12.2 ± 0.5 kg and 5.7 ± 0.2, respectively. No particular change associated with puberty was apparent for plasma concentrations of the metabolites examined. Plasma insulin concentrations were maintained at lower levels until the onset of puberty, and then they began to gradually increase. Plasma IGF-I concentrations began to gradually increase 1 to 4 weeks before the onset of puberty and this increase continued throughout the peripubertal period. These results imply that IGF-I acts as a peripheral nutritional signal to trigger the onset of puberty in Shiba goats. Key words: Puberty, Body growth, Metabolites, IGF-I, Shiba goat (J. Reprod. Dev. 50: [197][198][199][200][201][202][203][204][205] 2004) he onset of puberty is the result of a series of complex developmental events that occur within the reproductive endocrine axis. Just before the onset, there is a high frequency rhythm of gonadotropin-releasing hormone (GnRH) secretion and a sustained rise in basal luteinizing hormone (LH) secretion as the frequency of LH pulses increases, and the follicular phase begins, leading to the first LH surge and ovulation [1]. It has also been shown in heifers that the responsiveness of the pituitary gland to GnRH [2] and the action of estrogen on LH secretion [3] also change just before puberty. Numerous studies have demonstrated a close association between body growth, nutritional status and the timing of puberty onset. In cattle [4,5], sheep [6,7] and rodents [8,9], energy deficiency retards growth and delays the onset of puberty. Several lines of evidence from earlier investigations