Use of Intravaginal Progesterone-Releasing Device Results in Similar Pregnancy Rates and Losses to Long-Acting Progesterone to Synchronize Acyclic Embryo Recipient Mares

Abstract

The objectives of this study were: (1) to assess uterine features and serum progesterone concentrations of acyclic mares synchronized and resynchronized with intravaginal progesterone release device (IPRD), and (2) to compare pregnancy rates and losses of cyclic and acyclic embryo recipient mares treated with different synchronization protocols. In Experiment 1, mares (n = 12) received estradiol for 3 days (E2-3d), and then 24 h after the last injection, an IPRD was inserted and kept in place for 9 days. Three days after IPRD removal, mares were treated with E2-3d, and then a new IPRD was inserted and maintained for three days. Serum progesterone concentrations were assessed 2, 6, and 12 h after insertion and removal of IPRD, and then daily from the insertion of the first IPRD to one day after removal of the second IPRD. Experiment 2 was conducted with embryo recipient mares randomly assigned to four groups: (1) Cyclic: mares (n = 75) had ovulation confirmed after receiving a single dose of histrelin when a periovulatory follicle was first detected, (2) LAP4: acyclic mares (n = 92) were treated with E2-3d and then administered a single dose of LAP4 24 h after the last estradiol injection, (3) IPRD: acyclic mares (n = 130) were treated with E2-3d and an IPRD for 4-8 days, and (4) RE-IPRD: acyclic mares (n = 32) were synchronized as in the IPRD group but not used for embryo transfer (ET), then 8 to 15 days later, the mares were resynchronized with E2-3d and an IPRD for 4-8 days. In vivo-produced Day-8 embryos were collected and transferred 4-8 days after ovulation or progesterone treatments. Mares in IPRD and RE-IPRD groups had the intravaginal device removed immediately before ET, and then a new IPRD was inserted right after ET. Pregnancy diagnosis was performed at 5, 30, and 60 days after ET. Once pregnancy was confirmed, mares in the three acyclic groups received weekly injections of LAP4 (1.5 g) until 120 days of pregnancy. Mares in IPRD and RE-IPRD groups had the device removed three days after the first pregnancy diagnosis. In Experiment 1, progesterone concentrations increased rapidly starting 2 h after insertion of IPRD (p < 0.05); then, concentrations plateaued well above pregnancy maintenance until removal on days 9 and 3, respectively. Progesterone concentrations were reduced to baseline 24 h after IPRD removal (p < 0.05). For experiment 2, there was no difference in pregnancy rates across groups (65-74%) or pregnancy losses by 60 days of gestation (7-12%) (p > 0.05). In conclusion, the IPRD used herein resulted in a rapid increase and a sharp decline in progesterone concentrations upon its insertion and removal, respectively. Finally, our results demonstrated that IPRD could be a compatible alternative to LAP4 to synchronize and resynchronize acyclic embryo recipient mares.

Keywords: embryo transfer; equine; fertility; hormonal therapy; recipient mare.

Figure 1

Placement of an intravaginal progesterone device (IPRD) (Sincrogest, Ourofino) in an acyclic mare. (A) The IPRD in the operator’s hand immediately after being sprayed with oxytetracycline and hydrocortisone. (B) IPRD while being inserted into the vagina of an embryo recipient mare.

Figure 2

Timeline for blood sampling and hormone treatments administered to mares synchronized (IPRD) and resynchronized (RE-IPRD) with an intravaginal progesterone-releasing device (IPRD). Estradiol-17β (E2) (17 βeta^®, 10 mg, IM); IPRD (1 g of natural progesterone). Day 0 is equivalent to the day of ovulation. Initially, acyclic mares were treated with estradiol-17β for 3 days and then given an IPRD (Day 0). The IPRD was kept for nine days and then removed (Day 9). Mares were resynchronized three days after removal of the IPRD (i.e., Day 12, after the first synchronization). Estradiol-17β was given for three days (Day 12–Day 14), and then had a new IPRD inserted (Day 15) and removed three days later (Day 18).

Figure 3

Timeline for hormone treatments administered to synchronize and resynchronize embryo recipient mares for embryo transfer. Cyclic: cyclic mares having ovulation confirmed after induction of ovulation (follicle ≥35 mm) with histrelin acetate (250 µg); LAP4: acyclic mares treated with estradiol-17β for 3 days (E2-3d) and then administered a single dose of long-action progesterone (LAP4, 1.5 g); IPRD: acyclic mares treated with E2-3d and then given an IPRD containing 1 g of natural progesterone; RE-IPRD: acyclic mares synchronized as in the IPRD group but not used for embryo transfer, then 8 to 15 days later (i.e., D12–D23 after the first synchronization), the mares were resynchronized with E2-3d and IPRD for 4–8 days. Embryo transfers (ET) were performed between 4 and 8 days after ovulation or progesterone treatment. Pregnancy diagnosis (PD) was performed five days after ET (Days 9–13). Pregnant embryo recipient mares from groups LAP4, IPRD, and RE-IPRD received weekly injections of LAP4 at PD. Pregnant mares in Groups IPRD and RE-IPRD had the device removed three days after the first PD.

Figure 4

Endometrial edema scores of acyclic mares (n = 12) synchronized with estradiol and intravaginal progesterone release device (IPRD). (A) Mares treated with estradiol-17β for 3 days (D–3 to D–1) and then given an IPRD (D0). The IPRD was kept in place for nine days and then removed (D9). Mares did not have endometrial edema after day 3 (D3). (B) Mares were resynchronized three days post-removal of IPRD after the first synchronization. Mares were again treated with estradiol-17β for three days (R–3 to R–1) and then had a new IPRD inserted (R0). The IPRD was removed three days later (R3). Score 0 represents no edema, and score 4 represents exacerbated endometrial edema. D, day after treatment with IPRD; R, day after resynchronization with IPRD. Different super-scripts (^a,b) denote effect of days (p < 0.05).

Figure 5

Serum progesterone concentration at 2, 6, and 12 h after insertion (A), and removal (B) of intravaginal progesterone-releasing device (IPRD) in acyclic mares (n = 12). Acyclic mares were treated with estradiol-17β for 3 days and then given an IPRD (A, 0 h). The IPRD was kept for nine days and was then removed (B, 0 h). Different superscripts (^a,b,c) denote effect of time (p < 0.05).

Figure 6

Serum progesterone concentrations in acyclic mares (n = 12) treated with intravaginal progesterone-releasing device (IPRD). (A) Mares were treated with estradiol-17β for 3 days and then given an IPRD (D0). The IPRD was removed nine days later (D9). (B) Mares were resynchronized three days after removal of IPRD after the first synchronization. Mares were again treated with estradiol-17β for 3 days and then had a new IPRD inserted (R0). The IPRD was kept for three days (R3). D, day after treatment with IPRD; R, day after resynchronization with IPRD. Different superscripts (^a,b) denote effect of days (p < 0.05).

Figure 7

Pregnancy rates (A) and pregnancy losses (B) up to 60 days of cyclic and acyclic mares synchronized with long-acting progesterone (LAP4) or intravaginal progesterone-releasing device for the first time (IPRD, n = 130) or resynchronized with IPRD (n = 32) between 8 and 15 days after the first synchronization (RE-IPRD). Cyclic (n = 75): mares having ovulation confirmed after induction of ovulation (follicle ≥ 35 mm) with histrelin acetate (250 µg); LAP4 (n = 92): acyclic mares treated with estradiol-17β for 3 days and then administered a single dose of long-action progesterone (LAP4, 1.5 g); IPRD (n = 130): acyclic mares treated with estradiol-17β for 3 days and then given an IPRD containing 1 g of natural progesterone; RE-IPRD: mares not used after 8 days after insertion of an IPRD in the first synchronization were treated 8–15 days later with estradiol-17β for 3 days and then given a new IPRD. Embryo transfer was performed 4–8 days after ovulation or progesterone treatment and pregnancy diagnosis was performed 5 days later. Once pregnancy was confirmed, mares in the 3 acyclic groups received weekly injections of LAP4 (1.5 g) until 120 days of pregnancy. Mares in IPRD and RE-IPRD groups had the device removed three days after the first PD.