PATTERNS OF PLASMA-LH, FSH, ESTRADIOL AND CORTICOSTEROIDS FROM BIRTH TO THE 1ST ESTROUS-CYCLE IN MEISHAN GILTS

Hormonal changes associated with pubertal development in a breed of pi g exhibiting early puberty were determined. In Expt 1, blood from prep ubertal 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 da ys of age before (n = 16) or during (n = 9) the first oestrous cycle. Serial blood samples were collected through a jugular catheter at 20 m in intervals. In Expt 2, age at puberty was determined by daily examin ation for oestrus and weekly evaluation of plasma progesterone and fou nd to occur at 111 days of age. Hormone profiles determined at least 1 9 days before the first oestrus were grouped to constitute a prepubert al 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 50 days (0.42 versus 0.85 pulse h-1, P < 0.05), decreased between 50 and 70 d ays (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 da ys and decreased progressively until 80 days (7.2 and 2.3 ng ml-1, res pectively, at 20 and 80 days, P < 0.05). Concentrations of oestradiol and corticosteroids were highest at day 1 and showed nonsignificant fl uctuations between 10 and 90 days. The concentration of corticosteroid s 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 mi ld increase in number of LH pulses (P = 0.07) 11-13 days before pubert y, 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 morn ing concentration of cortisol (P = 0.06) 4-6 days before puberty. Afte r puberty, concentrations of LH (mean), FSH and progesterone were high er, 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 hig her progesterone concentration and amplitude of LH pulses. Hormonal ch anges in Meishan gilts therefore show a similar pattern to that observ ed 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 s timulation of follicular growth which leads to the first ovulation.