Embryo Transfer in Anovulatory Recipient Mares Treated with Estradiol Benzoate and Long-Acting Progesterone

Relationships between antral follicle count and reproductive characteristics of embryo-recipient mares

Mares (n = 77) were evaluated by antral follicle count (AFC) and selected as embryo recipients. Cyclic recipients received embryos between days 4-6 after ovulation. The acyclic recipients received an intramuscular (i.m.) protocol with 5mg of estradiol benzoate (EB) on the day of donor ovulation (D0; D-4 recipient), 3mg of EB on the following day (D1; D-3 recipient), and 3mg of EB (D2; D-2 recipient). Furthermore, 1500mg of progesterone (P4) i.m. given on D0 of the recipient (D4 donor) followed by 1500mg of P4 on the day of ET (D4-6 recipient). On the ET day, the AFC and animals' weight, body condition score (BCS), corpus luteum diameter, age and degree of uterine edema (UE) were measured. Pregnancy was confirmed on days 12 and 30. Low AFC was defined as ≤11 follicles (n = 43 mares) and high AFC as >11 follicles (n = 34 mares). Data were analyzed by a mixed effect model, including AFC group, reproductive seasonality, and season (P ≤ 0.05). UE was influenced (P = 0.05) by reproductive seasonality. The conception rate was higher (P = 0.016) in recipients with low (79.07 %) than high AFC (61.76 %) and higher (P = 0.005) in cyclic (81.40 %) than anestrus (58.82 %) mares. In addition, we observed a tendency (P = 0.06) for the interaction of AFC*reproductive seasonality, showing that high*anoestrus recipients had the lowest conception rate (37.50 %b) compared to high*cyclic (83.33 %a), low*anoestrus (77.78 %a) and low*cyclic (80 %a). The conception rate was higher in cyclic recipients with low AFC. Furthermore, UE was influenced by reproductive seasonality and mares in anestrus showed a higher degree of UE than cyclic mares.

Embryo transfer into anestrous recipient mares prepared using clomiphene citrate and short-acting progesterone

Embryo transfer (ET) is an important technology for genetic improvement programs in the equine industry. Many protocols have been used for preparation of recipients. This study evaluates a new protocol for preparation of acyclic embryo recipient mares using clomiphene citrate (CC) and short-acting oral progesterone (Altrenogest). Seventy-two native breed recipient mares were divided into 2 groups. Group 1(G1) included 60 non-cyclic mares with follicular structures ≤ 15 mm in diameter that received CC and Altrenogest. Group 2 (G2) included 12 cyclic recipient mares that served as a control group. G1 mares were treated with oral CC at a dose of 250 mg for 4 days followed by oral administration of Altrenogest for 6 days. Ultrasonography was carried out for evaluation of uterine echotexture response to hormonal treatment, and pregnancy diagnosis post ET. Serum estradiol and progesterone concentrations were also assessed. All data were statistically analyzed. The results revealed that the serum progesterone concentrations in G1 were higher than G2 (P < 0.001). There was no difference in the estradiol concentrations between both groups during diestrus phase (P > 0.05). The pregnancy rate was higher in G1 (83.3 %) than G 2 (66.6 %). In conclusion, using oral CC and Altrenogest, as a new protocol, was effective for preparation of acyclic recipient mares in this study.

Progesterone Device Use Improves Ovum Pick-Up Efficiency in Acyclic Donors

The aim of this study was to evaluate follicular dynamics and ovum pick-up (OPU) efficacy in untreated mares or mares treated with an intravaginal progesterone (P4) device during seasonal anestrus (acyclic) and during the breeding season (cyclic). Six mares (mean age = 5 years), were recruited into an ovum pick-up scheme that was performed every 14 days with and without the P4 device, during the acyclic and cyclic phases. Aspirations amounted to seven procedures with or without the P4 device during each phase. Five ultrasound assessments were performed at each interval between the OPUs. Data on follicular number and diameter as well as the numbers of recovered and the percentage of recovered oocytes were also collected. The number of follicles from mares in the acyclic phase was higher (P < .005) regardless of the treatment. However, the follicular diameter was smaller for the P4 group (P < .005) from the 2nd to the 5th evaluation post-OPU procedure. The percentage of oocytes recovered during the acyclic phase was higher for mares treated with the P4 device (P < .005). The P4 device resulted in follicles with smaller diameters and facilitated OPU efficacy.

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

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.

Intravaginal progesterone device (1.9g) and estradiol benzoate for follicular control in the mare during spring and summer

ABSTRACT The objective of this study was to evaluate follicular growth and ovulatory rates in mares treated with an intravaginal progesterone device (P4) during the 10-day period, associated with the use of estradiol benzoate (EB). The results were compared during the transition period (ET) in the spring and the breeding season in the summer (ER). The variables were submitted to ANOVA (Tukey's test), considering P<0.05. No ovulation occurred during the permanence of the P4 implant in both experimental periods. The ovulatory rate in the ER was 100% (n = 8) and in the ET 62.5% (n = 5; P = 0.0547). Significant differences were observed (<0.001), in both periods, comparing follicular growth rates during the permanence of P4 device (ER: 1.33 ± 0.89mm/d; ET: 1.00 ± 0.81mm/d) to the period without P4 (ER: 3.63 ± 1.33 mm/d; ET: 3.31 ± 1.66 mm/d). The present study demonstrated applicability and efficiency of a hormonal protocol using P4 intravaginal device and EB for follicular control in mares, both during ET and ER.

Artificial Long Estrus Protocols Administered Prior to Progesterone Increase Endometrial Uterocalin Expression in Anestrous Mares

Uterocalin (P19) is a lipocalin protein that has binding activity for the provisioning of the embryo with lipids, including those essential for morphogenesis and pattern formation. Therefore, it is thought that P19 plays an important role in supporting the survival of the early embryo. Previous research has shown that the endometrium from acyclic mares expressed more P19 following a simulated long estrus: treatment of 8 mg of estradiol benzoate (EB) split over five consecutive days, followed by long-acting progesterone administration (LA-P4) 72 hours later, when compared to a single 2.5 mg EB treatment. The main objective of this study was to evaluate if a new long estrus protocol, with fewer EB administrations, also increases endometrial uterocalin expression. Fifteen mares were assigned to three groups: long estrus 5 administrations (LE5; a total of 8 mg of EB in increasing doses was given over five consecutive days, Day -7 to Day -3); long estrus 2 administrations (LE2; 3 and 5 mg EB were given on Day -7 and Day -4); and short estrus (SE; a single dose of 2.5 mg EB was administered on Day -2). All groups received LA P4 on day 0 (D0). Daily ultrasonography and blood collections were performed to assess uterine edema and estradiol and progesterone plasma concentrations, respectively. Endometrial biopsies were collected on Day 4 to evaluate P19 expression by RT-qPCR. There were no differences in P19 expression between groups LE2 and LE5. However, P19 expression was higher (P < .05) in the LE groups than in the SE group. Both LE protocols produced high uterine edema (score 2-3) for at least 6 days. There was no effect of group (LE2 or LE5) on overall estradiol and progesterone concentrations (P > .1). In conclusion, the two EB administrations protocol is more feasible for preparing acyclic recipient mares at field conditions. However, a positive effect of the LE protocols on embryo survival and viability in anestrous treated mares still needs to be confirmed.

Timed artificial insemination in crossbred mares: Reproductive efficiency and costs

Timed artificial insemination (TAI) has boosted the use of conventional artificial insemination (CAI) by employing hormonal protocols to synchronize oestrus and ovulation. This study aimed to evaluate the efficiency of a hormonal protocol for TAI in mares, based on a combination of progesterone releasing intravaginal device (PRID), prostaglandin (PGF_2α ) and human chorionic gonadotropin (hCG); and compare financial costs between CAI and TAI. Twenty-one mares were divided into two groups: CAI group (CAIG; n = 6 mares; 17 oestrous cycles) and TAI group (TAIG; n = 15 mares; 15 oestrous cycles). The CAIG was subjected to CAI, involving follicular dynamics and uterine oedema monitoring with ultrasound examinations (US), and administration of hCG (1,600 IU) when the dominant follicle (DF) diameter's ≥35 mm + uterine oedema + cervix opening. The AI was performed with fresh semen (500 × 10⁶ cells), and embryo was recovered on day 8 (D8) after ovulation. In TAI, mares received 1.9 g PRID on D0. On D10, PRID was removed and 6.71 mg dinoprost tromethamine was administered. Ovulation was induced on D14 (1,600 IU of hCG) regardless of the DF diameter's, and AI was performed with fresh semen (500 × 10⁶ cells). On D30 after AI, pregnancy was confirmed by US. The pregnancy rate was 80.0% in TAIG and 82.3% in CAIG (p > .05). The TAI protocol resulted in 65% reduction in professional transport costs, and 40% reduction in material costs. The TAI was as efficient as CAI, provided reduction in costs and handlings, and is recommended in mares.

Effects of Equine Chorionic Gonadotropin on Ovulatory and Luteal Characteristics of Mares Submitted to an P4-Based Protocol of Ovulation Induction With hCG

The aim of this study was to evaluate the effect of equine chorionic gonadotropin (eCG) at the end of progesterone (P4) treatment on follicular and luteal characteristics during transition period (TP) and reproductive breeding season (RP). A total of 13 crossbred mares were distributed in two experimental groups in the spring and summer (n = 26). The animals received intravaginal P4 (1.9 g) releasing device from D0 to D10. On removal of P4 device, the mares received 400 IU of eCG (eCG group) or saline solution (control group). Human chorionic gonadotropin (hCG; 1.750 IU) was administered (DhCG) as soon as ovulatory follicle (OF) ≥35 mm was detected. Ovarian ultrasonography was performed from D0 until 15 days after ovulation. Blood samples were collected on D0, D5, D10, DhCG, 9 days after ovulation (CL9D), and 13 days after ovulation (CL13D). P4 and estradiol concentrations were assessed by chemiluminescence. Data were compared by Tukey test at P < .05. Ovulation rate was similar (P = .096) between seasons (RP = 100%; TP = 70%) but occurred earlier (P = .015) in RP (34.8 ± 10.1 hours) compared with TP (42.0 ± 10.4 hours). Interactions between season and treatment were observed for OF diameter (mm) (RP/control = 36.2 ± 1.8ab; RP/eCG = 32.9 ± 2.8 b; TP/control = 32.2 ± 1.2 b; TP/eCG = 37.2 ± 1.9a; P = .004) and for corpus luteum (CL) diameter (mm) on CL13D (RP/control = 25.4 ± 3.5a; RP/eCG = 22.5 ± 1.8ab; TP/control = 21.6 ± 4.9 b; TP/eCG = 27.4 ± 4.3a; P = .023), although no differences were observed for serum P4 on CL13D (RP/control = 6.0 ± 3.1 ng/mL; RP/eCG = 5.8 ± 0.9 ng/mL; TP/control = 3.6 ± 2.7 ng/mL; TP/eCG = 5.1 ± 2.3 ng/mL; P = .429) or for day of structural CL regression (RP/control = 12.8 ± 1.9; RP/eCG = 12.1 ± 1.1; TP/control = 11.0 ± 1.7; TP/eCG = 13.2 ± 2.0; P = .102). The application of eCG at the moment of P4 implant removal seemed to increase the capacity of luteal maintenance during spring TP. However, eCG treatment was worthless during the breeding season.

The mule (Equus mulus) as a recipient of horse (Equus caballus) embryos: Comparative aspects of early pregnancy with mares

The aim of this study was to compare the embryonic and early fetal development of horse embryos between recipient mules and mares from day 10-60 of pregnancy, in addition to hormonal (eCG and progesterone), ovarian, and uterine characteristics for approximately 4 months. Embryo donor mares (n = 5) and two groups of recipients (acyclic mules, n = 7; cyclic mares, n = 7) were used. Donor mares were monitored daily by transrectal ultrasonography and inseminated using fresh semen. Cyclic recipient mares were synchronized with the donor's ovulation using PGF2α and deslorelin acetate. Mules were prepared for the embryo transfers with estrogen and progestagen. Embryo collection and transfer were performed 8 days after ovulation of the donor mares. Pregnancy diagnosis with ultrasonography began 1 day after embryo transfer. After pregnancy confirmation, the recipient mules received long-acting progesterone once weekly for at least 120 days. The first day of detection (day 10) of an embryonic vesicle (EV) was similar between mules and mares. A period of extensive intrauterine mobility of the embryonic vesicle was observed similarly in mules and mares from days 10-17. The day of fixation of the EV in mules tended to be 1-day earlier than in mares; however, the diameter and growth rate of the EV did not differ between the two species. The embryo proper was first detected at day 20, and the crown-rump, width, and diameter were similar between the two recipient types. The heartbeat and allantoic sac tended to be detected 1 day later in mules than in mares, while the umbilical cord was first observed around day 40 in both species. Besides the expected differences found in ovarian aspects and eCG production, similar endometrial diameter, uterine tone and echotexture, and progesterone levels were seen between the two types of recipients. In conclusion, striking ultrasound similarities in equine embryo and fetal development, and uterine characteristics were seen between mules and mares used as recipients of horse embryos.

Endometrial Histomorphometry of Anestrous Mares Under the Influence of Different Embryo Transfer Hormonal Protocols

Aiming to investigate the effects of different hormonal protocols on the endometrium morphometry of anestrous mares, 26 animals were assigned to four different treatment groups: (1) EB2.5LAP4: single dose of 2.5 mg of estradiol benzoate (EB); (2) EB5LAP4: 5 mg of EB in 2 consecutive days; (3) EB10LAP4: 10 mg of EB in three consecutive days, considering that all EB-treated groups received a single dose of 1,500 mg of long-acting progesterone (LA P4) after the single/last EB dose; and (4) LAP4: only 1,500 mg of LA P4. Results were also compared with those found in cyclic mares (control group). Endometrial biopsies were collected before and after the hormonal treatments in anestrous mares, and during estrus and at 5 days after ovulation in cyclic mares (D5). Samples were prepared for histological and histomorphometric analysis. Tissue sections were examined to determine luminal epithelium height (LEH), glandular epithelium height (GEH), endometrial thickness (ET), and glandular density (GD). Similar morphometric changes were observed after EB and P4 were administered to groups EB5LAP4 and EB10LAP4. Five days after LA P4 administration (D5), all the assessed variables were similar between all EB-treated groups. In addition, all variables of the EB-treated groups were similar to the control group on D5. Although most of the LAP4 group variables on D5 were similar to the EB-treated groups (except GD), reduced GD and GEH were found when compared with the control group, demonstrating the importance of estradiol priming before P4 on glandular activity and density.

Evaluation of environmental effects on reproductive characteristics of Mangalarga Marchador mares in a commercial embryo transfer program

The objective of this study was to evaluate the environmental effects on embryo recovery rate and pregnancy rate of Mangalarga Marchador mares. The reproductive characteristics of donor and recipient mares were evaluated during five years in Brazilian tropical environment. The mares were used throughout the year and seasons were classified as: October to April (breeding season - BS); May (autumn transition out of the breeding season - ATBS); June to August (non-breeding season - nBS); and September (vernal transition into the breeding season - VTBS). Daily temperature rainfall and hours of daylight (photoperiod) were measured during all months and years of evaluation. The embryo recovery rate (ERR) and the pregnancy rate (PR) were observed and frequencies were calculated. The effect of environmental variables, day of flushing, and hormonal treatments (estradiol benzoate and progesterone) were determined for the reproductive measures using the Chi-square and Kruskal-Wallis tests. Significant effects were noted of the year, season and temperature on ERR (P < 0.05), but no significant effects were observed of the environmental parameters (year, season, hormone treatment, rainfall and photoperiod) on PR (P > 0.05). The day of uterine flush affected ERR (P < 0.05) but did not affect PR (P > 0.05). In addition, hormone treatment also supported favorable results of PR in recipient mares during nBS. The conclusion is that mares of this breed can be used in reproduction all year long, with good pregnancy rates, in Brazil's tropical environment. The hormone treatment also supported favorable pregnancy rates in recipient mares during the non-breeding season. It seems that mares can have good pregnancy rates throughout the year in Brazil´s tropical environment.

Embryo transfer in competition horses: Managing mares and expectations

Embryo transfer (ET) is an accepted and successful technique for obtaining foals from mares without interrupting their competition careers. Recent research, however, suggests that the potential of factors including heat, exercise, repeated embryo flushing and repeated manipulation of the reproductive cycle using exogenous hormones to have a negative impact on fertility may have been underestimated. This paper reviews the evidence base for involvement of these factors in repeated failures to recover embryos from nongeriatric competition mares without obvious clinical or pathological indications of reproductive abnormalities. It concludes that, for some mares at least, a cessation of exercise for the periovulatory period and the period between ovulation and embryo flushing, combined with careful management of flushing-induced endometritis, and minimal hormonal manipulation of the reproductive cycle, may be necessary to optimise embryo recovery rates. Mare owners may have been encouraged to request ET for their mares following high-profile examples in the media of elite mares that have produced foals by ET whilst competing. The veterinarian should educate mare owners about the multiple factors that may affect the chances of recovering an embryo from their mares, and should manage the expectations of mare owners so that they do not approach ET programmes in the expectation that there will be no disruption to their training and competition plans.