Uterine and ovarian responses to puberty induction and pregnancy in prepubertal gilts

We evaluated the effect of age on response to puberty induction in gilts. Sequential treatment with a commercial gonadotropin mixture (400 IU PMSG, 200 IU hCG) followed 96 h later with hCG (500 IU) was used to induce follicular growth and ovulation, respectively. In the first experiment, gilts (84, 104, 124, 144, and 164 d old) were used. Peripheral blood was collected on d 0 (before treatment) and on d 2, 3, 4, 8, and 16 after treatment. On d 16, all gilts were hysterectomized, uterine flushings were collected, and uterine weight (UTWT) and length (UTLG) were measured. For treated gilts, UTWT, UTLG, number of corpora lutea (CL), peripheral progesterone (P4) on d 16, and estradiol (E2) on d 4 increased (P < .05) linearly with age. Uterine luminal PGE (P < .05) and PGF (P = .07), expressed per UTWT, responded quadratically with age; gilts treated at 124 d of age or older showed decreased amounts. Overall, the number of CL correlated positively (P < .01) with UTWT and P4 on d 8 and 16. Peripheral P4 on d 4, 8, and 16 (P < .10) and E2 on d 0 and 4 (P < .01) were correlated positively with uterine weight on d 16. Gilts induced to ovulate at 104 and 144 d of age had heavier and longer uteri (P < .01), more P4 on d 8 and 16 (P < .05), and more E2 on d 2 (P < .1) and 4 (P < .05) than controls at the same age. The second experiment evaluated pregnancy success for gilts induced to ovulate at 116 vs 151 d of age. The effects of induction of two consecutive estrous cycles also were evaluated. Two of seven (28.6%) and four of nine (44.4%) gilts first treated when 116 and 151 d old but none of seven gilts treated at 96 and 116 d of age were pregnant 60 d after insemination. Results indicate that induction of a prior cycle did not improve pregnancy rates. However, some gilts in this population maintained pregnancies to 60 d when induced to ovulate and inseminated at 120 d of age.