UTERINE AND OVARIAN RESPONSES TO PUBERTY INDUCTION AND PREGNANCY IN PREPUBERTAL GILTS

We evaluated the effect of age on response to puberty induction in gil ts. Sequential treatment with a commercial gonadotropin mixture (400 I U PMSG, 200 IU hCG) followed 96 h later with hCG (500 IU) was used to induce follicular growth and ovulation, respectively. In the first exp eriment, gilts (84, 104, 124, 144, and 164 d old) were used. Periphera l blood was collected on d 0 (before treatment) and on d 2, 3, 4, 8, a nd 16 after treatment. On d 16, all gilts were hysterectomized, uterin e flushings were collected, and uterine weight (UTWT) and length (UTLG ) were measured. For treated gilts, UTWT, UTLG, number of corpora lute a (CL), peripheral progesterone (P-4) on d 16, and estradiol (E-2) on d 4 increased (P < .05) linearly with age. Uterine luminal PGE (P < .0 5) 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 P-4 on d 8 and 16. Peripheral P-4 on d 4, 8, and 16 (P < .10) and E-2 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 P-4 on d 8 and 16 (P < .05), and mor e E-2 and 2 (P < .1) and 4 (P < .05) than controls at the same age. Th e second experiment evaluated pregnancy success for gilts induced to o vulate at 116 vs 151 d of age. The effects of induction of two consecu tive 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 i nsemination. Results indicate that induction of a prior cycle did not improve pregnancy rates. However, some gilts in this population mainta ined pregnancies to 60 d when induced to ovulate and inseminated at 12 0 d of age.