Hormone supplementation protocol using estradiol benzoate and long-acting progesterone is efficient in maintaining pregnancy of anovulatory recipient mares during autumn transitional phase

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.

Plasma estradiol profile after administration of different types of estradiol esters in acyclic mares

Although the use of different estradiol esters has been extensively studied in hormonal protocols in cows, such information is lacking in mares. The present study aimed to assess the effects of treatment with the same doses and administration frequency of estradiol cypionate, estradiol benzoate and 17β estradiol on plasma estradiol (E2) concentrations of acyclic mares and correlate the E2 profile to the endometrial edema score. Sixteen treatments were performed in 14 mares randomly divided into three groups: EB (n=5), EC (n=5) and 17β (n=6), receiving 10mg on day 0 (D0), 6mg on D1 and 4mg on D2 of estradiol benzoate, estradiol cypionate, and estradiol 17β, respectively. Blood samples, rectal palpations and ultrasound evaluations were performed once daily, starting before the first estradiol treatment (D0) until edema disappearance or D8. Moderate to high edema was observed in all groups 24h after the first estradiol administration. Edema persisted above score 2 until D7, D5 and D4 in groups EC, EB and 17β, respectively. Higher edema was found on D2 in EB group compared to 17β, on D6 and D7 in EC compared to 17β, and on D8 in EC compared to EB (p≤0.05). Maximum E2 concentrations were detected on D1 in groups: EB, showing a sharp decrease from D2 to D3 (p<0.0001); and 17β, where no differences were observed between treatment days (p≥0.05). In the EC group, maximum concentrations were observed on D2, which remained high from D2 to D4 compared to the other days (p<0.0001). Plasma concentration of E2 was higher in EB than the other groups on D0 and D1, and EB>EC>17β on D2. Plasma E2 concentrations and edema score were positively correlated, being moderate in groups EB and EC and weak in the 17β group. In conclusion, the most pronounced plasma E2 concentration was observed in EB group 24h after the administration of the first dose. Estradiol concentrations peaked 48h after EC administration, while a distinct peak was not observed in a 24h interval evaluation in the 17β group. Moreover, high edema does not necessarily reflect on high E2 concentrations in acyclic mares.

The Effect of Treatment with Oestradiol Benzoate on Oestrus Expression and Endometrial Oedema in Anovulatory and Cyclic Mares

Oestrogens treatment is often used to induce oestrus behaviour in anoestrous mares to aid in the collection of stallion semen and as recipient mares to receive embryos when combined with progesterone. However, there are no studies to describe the effect of dose and individual mare on the intensity and duration of the response, in both anoestrous and cyclic mares. In Experiment 1, 13 anoestrous mares were treated with one of five doses of oestradiol benzoate (OB) (1, 1.5, 2, 3 and 4 mg) per mare in five consecutive treatment periods (n = 65), to determine the response in terms of endometrial oedema and oestrous behaviour. Experiment 2 and 3 used 3 mg of OB in cyclic mares to confirm or deny the presence of an active corpus luteum (CL). There was a dose rate of OB and individual mare effect (p < 0.05) on the intensity and persistence of endometrial oedema and oestrous behaviour. A total of 2 mg OB was enough to induce endometrial oedema and oestrous behaviour within 48 h in most mares. Mares with an active CL did not show endometrial oedema following treatment of 3 mg OB.

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.

Serum Progesterone and Conception Rates in Acyclic Embryo Recipient Mares Using a Bovine Progesterone-Releasing Intravaginal Device

The objective of this study was to quantify serum progesterone levels, uterine features, and pregnancy rates in acyclic, embryo recipient mares using a bovine progesterone-releasing intravaginal device in a commercial embryo transfer (ET) program. The study included 73 recipient mares of unknown breed, aged 3-10 years, weighing 350-500 kg, and kept under an intensive management system on Tifton 85 (Cynodon spp.) pastures with water and mineral salt ad libitum. The horses were divided into two groups: a group with a progesterone-releasing intravaginal device (1 g progesterone, G-IVP4, n = 24) and a control group (G-iP4, n = 49) receiving an injection of 1,500 mg long-acting progesterone. Jugular blood was collected for the G-IVP4 group for subsequent progesterone measurement by radioimmunoassay on three occasions: Day 0 (D0), intravaginal device was placed; Day 5 (D5), day of the ET; and Day 9 (D9), day of pregnancy diagnosis. There was an increase (P < .0001) in serum progesterone levels on D5 and D9 compared with D0 (4.09 ± 0.81 and 6.45 ± 1.03 ng/mL vs. 0.71 ± 0.14 ng/mL). There were no differences among groups in the pregnancy rate (P > .05), with rates of 83.33% and 73.46% for G-IVP4 and G-iP4, respectively. In conclusion, the intravaginal route for absorption of 1 g of progesterone device increased the serum level of progesterone sufficiently to prepare the uterus of acyclic recipient mares for ET, and the conception rate was similar to the standard protocol using long-acting injectable progesterone.

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.

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.