During pubertal maturation, the increase in blood concentrations of sexual steroids is associated with a spurt in plasma IGF-I in primates, rats and cattle. However, data on the influence of sex steroids on plasma IGF-I during this physiological period are contradictory. Therefore, the present experiment was undertaken to understand better the relationships between pubertal development, energy metabolic regulation and the IGF-I/IGFBP system in crossbred gilts (Large White x Landrace). Circulating concentrations of hormones and metabolites were examined in ovariectomized (n = 6) and sham-operated females (n = 9) during sexual development. Surgery and first blood samplings were performed at 70 days of age. Growth curves were similar in ovariectomized and entire females. First oestrus and ovulation occurred between 178 and 209 days in entire gilts. From 84 days of age, plasma FSH concentration was lower in sham-operated than in ovariectomized gilts (P < 0.01) showing the negative feedback exerted by ovarian secretions on the gonadotrophin axis in entire gilts. Preprandial concentration of plasma glucose was not influenced by age whereas plasma free fatty acids decreased with age (P < 0.01). Concentrations of both metabolites were similar in ovariectomized and entire gilts. Plasma IGF-I and 43-39 kDa IGFBP levels increased whereas plasma 34 kDa IGFBP decreased with age (P < 0.01) and none of the levels differed between ovariectomized and entire gilts (P > 0.1). This experiment shows that gonadal steroids are not involved or play only a minor role in the control of IGF-I and IGFBP plasma levels during pubertal development in the female pig.
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