Changes in luteinizing hormone concentrations after abortion, parturition, and weaning in primiparous sows

Abstract

This study compared the endocrine changes associated with the capacity of gilts to return to estrus following mid-gestation abortion, removal of piglets at birth (zero weaned), during lactation, and following the removal of piglets after lactation (weaned). Serum concentrations of luteinizing hormone (LH), estradiol-17β (E 2), and progesterone (P 4) were determined in aborted gilts (Group 1; n = 5), zero-weaned gilts (Group 2; n = 6), and gilts (Group 3; n = 6) weaned after a 3 week lactation. In addition, postpartum endocrine changes were compared between Group 2 and Group 3 gilts during lactation. The day of abortion, parturition and weaning was considered Day 0. Blood samples were collected at 6 h intervals from Day —2 to Day 21 and at 15-min intervals for 8 h on Days —2, 1, 4, 7, 10 and 14. Following each 8 h sampling period, gilts were treated i.v. with gonadotropin releasing hormone (GnRH) at 0.5 μg kg −1 body weight (BW) and blood samples collected at 10-min intervals for 3 h. Estrus was detected using twice daily boar exposure. The number of gilts exhibiting estrus were four, four and one at 4.5 ± 0.3 days, 14.8 ± 0.5 days and 9 days for aborted, zero-weaned, and weaned groups, respectively. Gilts exhibited increasing LH concentrations with time following abortion, while GnRH-induced LH release was not affected by group or time. Changes in E 2 and P 4 concentrations reflected the endocrine changes associated with gestation or the return to estrus for each group. In addition, LH, E 2 and P 4 concentrations were similar in lactating and zero-weaned gilts for 7 days following parturition. It was evident that gilts aborted during mid-gestation have an increased ability to return to estrus than zero-weaned gilts, and that pituitary responsiveness to exogenous GnRH did not differ between groups nor was affected by the termination of pregnancy or lactation.