Patterns of plasma LH, FSH, oestradiol and corticosteroids from birth to the first oestrous cycle in Meishan gilts

Abstract

Hormonal changes associated with pubertal development in a breed of pig exhibiting early puberty were determined. In Expt 1, blood from prepubertal Meishan gilts was collected at about 1 (n = 5), 10 (n = 5), 20 (n = 4), 30 (n = 5), 50 (n = 5), 70 (n = 10), 80 (n = 10) and 90 (n = 7) days of age. In Expt 2, females were sampled between 99 and 116 days of age before (n = 16) or during (n = 9) the first oestrous cycle. Serial blood samples were collected through a jugular catheter at 20 min intervals. In Expt 2, age at puberty was determined by daily examination for oestrus and weekly evaluation of plasma progesterone and found to occur at 111 days of age. Hormone profiles determined at least 19 days before the first oestrus were grouped to constitute a prepubertal stage. In Expt 1, mean concentration of LH was high at 1 day of age, significantly lower at 10 days and showed nonsignificant variations until 90 days. Frequency of LH pulses increased between 10 and so days (0.42 versus 0.85 pulse h-1, P < 0.05), decreased between 50 and 70 days (0.49 pulse h-1, P < 0.05) and remained low thereafter. Amplitude of LH pulses was high between 1 and 30 days and declined progressively until 80 days. Mean concentration of FSH was high between 1 and 20 days and decreased progressively until 80 days (7.2 and 2.3 ng ml-1, respectively, at 20 and 80 days, P < 0.05). Concentrations of oestradiol and corticosteroids were highest at day 1 and showed nonsignificant fluctuations between 10 and 90 days. The concentration of corticosteroids was higher in the morning than in the afternoon (P < 0.05) whatever the age. In Expt 2, comparisons with the prepubertal stage showed a mild increase in number of LH pulses (P = 0.07) 11-13 days before puberty, an increase in mean (P = 0.07) and baseline concentration (P < 0.05) of LH, in oestradiol concentration (P < 0.05) and a decrease in morning concentration of cortisol (P = 0.06) 4-6 days before puberty. After puberty, concentrations of LH (mean), FSH and progesterone were higher, whereas morning cortisol was lower at the beginning of the luteal phase than during the prepubertal stage (P < 0.05). At the end of the luteal phase, the only differences with the prepubertal stage were higher progesterone concentration and amplitude of LH pulses. Hormonal changes in Meishan gilts therefore show a similar pattern to that observed in European breeds of pig with a perinatal, an infancy, a juvenile and a waiting phase. Four to 13 days before puberty an increase in LH and a decrease in corticosteroid secretions are probably involved in stimulation of follicular growth which leads to the first ovulation.