Effect of hCG in the Presence of hCG Antibodies on the Follicle, Hormone Concentrations, and Oocyte in Mares

Relationship Between Ovulation and Body Temperature in the Mare: A Preliminary Study

In the equine industry, monitoring of the reproduction cycle is key to be able to produce one foal per mare and per year. Ovulation detection is difficult partly due to the variability of the estrus length. Currently, the most reliable method for ovulation detection is transrectal ultrasonography. This technique, however, implies handling of the mare as well as veterinary costs. The aim of this experimentation is to study body temperature variations around ovulation. Nine reproduction cycles were monitored around ovulation. Transrectal ultrasonographies were performed each day as well as blood sampling to dose estradiol-17β and progesterone to confirm ultrasonographic results. Body temperature was automatically recorded every 10 minutes using an identification chip equipped with a temperature sensor implanted in the mares' neckline. Data were analyzed using linear mixed models. Daily body temperature pattern did not vary between the phases of the reproductive cycle (follicular, ovulatory and luteal). Temperature differences between phases, however, were identified and appeared hourly-specific. There was an increase of temperature at ovulation compared to the end of the follicular phase ranging from 0.51°C ± 0.21°C to 0.92°C ± 0.26°C and occurring between 04:30 and 08:00. Moreover, a significant increase of body temperature was measured during the first days of luteal phase, ranging from 0.29°C ± 0.17°C to 0.60°C ± 0.16°C, between 10:30 and 16:00. Body temperature varied around ovulation and it might be a promising tool for mare reproduction monitoring. A more complete study, however, focusing on the whole cycle is required.

Graduate Student Literature Review: Effects of human chorionic gonadotropin on follicular and luteal dynamics and fertility in cattle

Circulating progesterone concentrations during the growth of the ovulatory follicle and early embryo development have been positively associated with embryo quality and survival and pregnancy success. As a potent luteotropic agent with LH-like activity, human chorionic gonadotropin (hCG) has been tested in different studies to improve pregnancy outcomes by increasing circulating progesterone concentrations during the growth of the ovulatory follicle or early embryonic development. Nevertheless, hCG has produced inconsistent, contradictory, and intriguing results. Furthermore, recent research indicates that hCG, when used before artificial insemination, may affect physiological events necessary for the ovulation of a viable oocyte. In addition, the use of hCG-inducing accessory corpus luteum during the estrous cycle seems to disturb luteolysis and follicle and luteal dynamics during the estrous cycle. This literature review discusses past and current research exploring the effects of hCG on the estrous cycle characteristics and pregnancy per artificial insemination and embryo transfer.

Hormonal Management for the Induction of Luteolysis and Ovulation in Andalusian Jennies: Effect on Reproductive Performance, Embryo Quality and Recovery Rate

Two prostanglandins (luprostiol, LUP, and dinoprost, DIN) and two ovulation-inducing agents (human Chorionic Gonadotropin, hCG, and deslorelin, DES) were evaluated for luteolysis and estrus induction, and for ovulation induction, respectively, in embryo donor jennies. Twenty-six fertile Andalusian jennies were used. In Experiment 1, jennies (n = 112 cycles) were randomly treated with either LUP or DIN after embryo flushing. In Experiment 2, donors (n = 84 cycles) were randomly treated with either hCG or DES to induce ovulation. No differences were found between prostaglandins for all variables studied (prostaglandin–ovulation interval (POI), interovulatory interval (IOI), embryo recovery rate (ERR), positive flushing rate (PFR) and embryo grade (EG)). The ovulation rate was similar for hCG and DES (60.9% vs. 78.7%). However, the interval to ovulation (ITO) was affected (62.61 ± 7.20 vs. 48.79 ± 2.69 h). None of the other variables studied (ERR, PFR and EG) were affected (p > 0.05), except for embryo quality (p = 0.009). In short, both prostaglandins evaluated are adequate to induce luteolysis and estrus. Both ovulation-inducing agents hastened ovulation, but DES seems to be more effective than hCG. Follicular diameter affected the interval from treatment to ovulation, and high uterine edema was related to low embryo quality.

Hemodynamic, endocrine, and gene expression mechanisms regulating equine ovarian follicular and cellular development

Ovulatory follicle development and associated oocyte maturation involve complex coordinated molecular and cellular mechanisms not yet fully understood. This study addresses the relationships among follicle diameter, follicle wall blood flow, follicular-fluid factors, and gene expression for follicle growth, steroidogenesis, angiogenesis, and apoptosis in granulosa/cumulus cells and oocytes during different stages from the beginning of largest/ovulatory follicle to impending ovulation in mares. The most remarkable findings were (i) a positive association between follicle development, follicle blood flow, intrafollicular follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, progesterone, and messenger RNA (mRNA) expression for FSHR and LHCGR in granulosa cells of the largest/ovulatory follicle; (ii) a plateau or decrease in follicle diameter and blood flow and granulosa cell mRNA for FSHR, LHCGR, IGF1R, VEGFR2, CYP19A1, and CASP3 at the preovulatory stage; (iii) higher StAR and BCL2 and lower CASP3 mRNA in granulosa cells at the time of impending ovulation; (iv) greater IGF1R mRNA for granulosa cells at the predeviation stage; and (v) lower FSHR, LHCGR, IGF1R, and VEGFR2 mRNA in cumulus cells and greater LHCGR and IGF1R mRNA in oocytes at the ovulatory stage. This study is a critical advance in the understanding of molecular mechanisms of follicle development and oocyte maturation and is expected to be vital for future studies targeting potential markers.

Comparative Efficacy of Histrelin Acetate and hCG for Inducing Ovulation in Brazilian Northeastern Jennies (Equus africanus asinus)

The goal of this study was to compare the efficiency of histrelin acetate (GnRH analog) and human chorionic gonadotropin (hCG) to hasten ovulation in Brazilian Northeastern jennies (Equus africanus asinus). Thirty cycles of ten jennies were randomly assigned in one of the three groups: G0 (control group), saline; G1, 250 μg of histrelin acetate; G2, 2500 IU of hCG. Jennies were evaluated by transrectal palpation and ultrasonography, and had the administration of an ovulation-inducing agent when a follicle measuring between 29 and 32 mm of diameter was diagnosed. Jennies were monitored every 6 hours by transrectal ultrasonography until ovulation. The interval between prostaglandin administration and ovulation was lower (P < .05) in jennies from the G1 (145.2 ± 34.6 hours) and G2 (147.4 ± 27.3 hours) groups compared with the control cycle (220.0 ± 41.8 hours). Both treatments (G1, 41.15 ± 3.5 hours; G2, 37.8 ± 2.5 hours) also reduced (P < .05) the interval that jennies took to ovulate after the administration of the ovulation-inducing agent compared with the control (81.8 ± 28.8 hours). All jennies from G1 and G2 ovulated up to 48 hours after ovulation induction, whereas 100% of jennies in the control cycle ovulated later (>48 hours from the administration of saline). In conclusion, both histrelin acetate and hCG at the used dose are efficient ovulation-inducing agents in jennies promoting ovulation up to 48 hours after administration.

Single injection of triptorelin or buserelin acetate in saline solution induces ovulation in mares the same as a single injection of hCG

The aim of this study was to assess the efficacy of different doses of buserelin acetate and another GnRH agonist, triptorelin acetate, in saline solution in a single subcutaneous injection, to induce ovulation of growing pre-ovulatory follicle in mare and compare it with the classical treatment of a single injection of hCG. The study is split into 3 experiments over different breeding seasons in the same stud with a random distribution of treatment. The first one was to compare the injection of 6 mg of buserelin with 1,500 IU of hCG; the second one consisted of comparing different doses of buserelin (6 mg and 3 mg); and the third one compared three different doses of buserelin (3, 2 and 1 mg), 0.1 mg of triptorelin with 1,500 IU of hCG as a control group. The results of all experiments showed the same efficacy between all treatments with mares ovulating between 24 and 48 hr after injection: experiment 1: hCG (78% n = 41) and buserelin 6 mg (90% n = 50); experiment 2: buserelin 6 mg (78,1% n = 192) and buserelin 3 mg (78% n = 341); and experiment 3: hCG (87% n = 106), buserelin 3 mg (84,7% n = 137), buserelin 2 mg (82,7% n = 104), buserelin 1 mg (87% n = 54) and triptorelin 0.1 mg (84,7% n = 72). In conclusion, this study contributes to erasing the dogma that has been established since 1975 that a single injection in solution without any long-acting excipient of a GnRH agonist cannot induce ovulation in the mare. This study also shows that a injection of 0.1 mg of triptorelin in solution is a good alternative for ovulation induction and is comparable to small doses of buserelin acetate in solution (1 mg) and 1,500 IU of the gold standard trigger hCG, mainly in countries where human formulation of buserelin is not available.

Effect of Timing of Postovulatory Insemination Relative to Human Chorionic Gonadotropin/Buserelin Treatment With 1 Straw of Frozen-Thawed Semen on Mare Fertility

The reproductive management of mares for frozen semen artificial insemination (AI) can be costly and labor intensive. Predicting the exact time of ovulation can be challenging even when ovulation-inducing drugs are used. The main objective of this retrospective study was to determine whether there was an effect of interval between examinations to detect ovulation on likelihood of pregnancy and early embryonic loss in mares after postovulatory breeding with a single straw of frozen/thawed semen. The second objective was to determine the efficacy of two different drugs (human chorionic gonadotropin vs. buserelin) for timely induction of ovulation. The length of the interval from penultimate check to ovulation had no significant effect on pregnancy or embryo loss rates (4 hours: 34.1% and 13.3% vs. 8 hours: 26.1% and 0% and 16 hours: 34.5% and 10%, respectively) nor did the ovulation-inducing drug used, number of the cycle, or the stallion. In conclusion, there appears to be no advantage of checking mares for ovulation during the late evening and night hours when using a postovulatory AI protocol and ovulation-inducing drugs.

Follicle vascularity coordinates corpus luteum blood flow and progesterone production

Colour Doppler ultrasonography was used to compare the ability of preovulatory follicle (POF) blood flow and its dimensions to predict the size, blood flow and progesterone production capability of the subsequent corpus luteum (CL). Cows (n=30) were submitted to a synchronisation protocol. Follicles ≥7mm were measured and follicular wall blood flow evaluated every 12h for approximately 3.5 days until ovulation. After ovulation, cows were scanned daily for 8 days and similar parameters were evaluated for the CL. Blood samples were collected and plasma progesterone concentrations quantified. All parameters were positively correlated. Correlation values ranged from 0.26 to 0.74 on data normalised to ovulation and from 0.31 to 0.74 on data normalised to maximum values. Correlations between calculated ratios of both POF and CL in data normalised to ovulation and to maximum values ranged from moderate (0.57) to strong (0.87). Significant (P<0.0001) linear regression analyses were seen in all comparisons. In conclusion, higher correlations were observed between the dimensions of POF and/or CL and blood flow of both structures, as well as POF and/or CL blood flow with plasma progesterone concentrations of the resultant CL. These findings indicate that follicle vascularity coordinates CL blood flow and progesterone production in synchronised beef cows.

Influence of two ovulation-inducing agents on the pituitary response and follicle blood flow in mares

The objective of the current study was to evaluate the effects of deslorelin and hCG, two ovulation-inducing therapies, on LH surge and follicle vascularity in mares. Thirty mares were either treated with 1.5 mg IM of deslorelin, 2,500 IU IV of hCG or 2 mL IM of NaCl 0.9% (GnRH, hCG and Saline groups, respectively). Power-flow Doppler examination and blood collection were performed every hour during the first 12 hours after treatment (H0) and every six hours between hours 12 (H12) and 30 (H30) after treatment. Moreover, endpoints were evaluated every hour through the last six hours before ovulation (OV-6 to OV-1). In GnRH group, plasma LH concentration progressively increased (P < 0.001) during the first 6 hours after treatment and remained high (P > 0.1) until OV-1. A significant increase in LH concentrations was first detected (P < 0.05) at 24 hours after treatment in hCG group, while no changes (P > 0.1) on LH levels were found during H0-H30 and between OV-6 and OV-1 in the Saline group. Independent of the treatment, significant variations on the percentage of the follicle wall with Doppler signals were not observed (P > 0.1) throughout the entire experiment. A weak correlation between the preovulatory follicle vascularity and the plasma LH concentration was found in GnRH, hCG and Saline groups (r = +0.29, +0.29 and -0.23, respectively; P ˂ 0.0001). These results described for the first time the immediate and continuous pituitary response to ovulation-inducing therapy with injectable deslorelin. Moreover, spontaneous and induced ovulations were not preceded by an increased follicle vascularity, which differs from previous reports in large animals.

Changes in intrafollicular concentrations of free IGF-1, activin A, inhibin A, VEGF, estradiol, and prolactin before ovulation in mares

Changes in intrafollicular growth factors and hormones were evaluated in vivo in postdeviation and impending ovulation follicles. Mares (n = 30) were randomly assigned to five experimental groups based on target diameters of 25, 30, 35, 40 mm, and impending signs of ovulation. Furthermore, data belonging to two or more proximal diameter groups that were not different were combined and regrouped for each factor separately. Follicular fluid-free insulin-like growth factor 1 was highest (P < 0.003) in 35-mm follicles, followed by the 40-mm and impending ovulation follicle group, and the 25- to 30-mm follicle group. However, concentrations of insulin-like growth factor binding protein 2 in follicular fluid did not differ (P > 0.05) among groups. Additionally, follicular fluid activin A tended (P < 0.06) to be higher in impending ovulation follicles when compared with the 25- to 40-mm follicle group. Concentrations of intrafollicular estradiol were higher (P < 0.0001) in 40-mm and impending ovulation follicles than in the other follicle groups. Follicular fluid concentrations of inhibin A and vascular endothelial growth factor were lower (P < 0.05) in the 40-mm and the impending ovulation follicle group when compared with the 25- to 35-mm follicle group. Systemic and intrafollicular prolactin levels were lower (P < 0.05) in the impending ovulation group when compared with the 25- to 40-mm follicle group. Prolactin concentrations were higher (P < 0.05) in the follicular fluid than in the plasma. The novel findings of this study, a decrease in intrafollicular-free insulin-like growth factor 1, inhibin A, vascular endothelial growth factor, and prolactin during the final stages of follicular growth, document for the first time the occurrence of dynamic changes among intrafollicular factors and hormones during the stages of follicle dominance and as ovulation approaches.

Ultrasound characteristics of experimentally induced luteinized unruptured follicles (LUF) and naturally occurring hemorrhagic anovulatory follicles (HAF) in the mare

The development of hemorrhagic anovulatory follicles (HAF) involves luteinization and hemorrhage of the follicle. This is observed on ultrasound as an increase in the echogenicity of the granulosa layer and formation of echoic particles in the antrum. The inhibition of prostaglandin synthesis with flunixin meglumine (FM) during the periovulatory period induces ovulatory failure with development of luteinized unruptured follicles (LUF). These two types of anovulatory follicles appear to share similar ultrasound features but they have not been compared critically. The following endpoints: follicle diameter, follicular contents score, interval from hCG administration to beginning of follicular hemorrhage, interval from hemorrhage to organization of follicular contents, and cycle length were studied and compared in mares with HAF (n = 11) and LUF (n = 13). The objective of this study was to elucidate whether these two unruptured follicles have a consistent clinical pattern of development and therefore can be considered as part of the same anovulatory syndrome. None of the endpoints analyzed differed significantly between HAF and LUF. However, there was a greater individual variation in HAF as compared with LUF in regards to interval from hCG to hemorrhage, follicular diameter at the administration of hCG, and beginning of hemorrhage. In conclusion, HAF share a similar cascade of ultrasound characteristics with the experimentally induced LUF. This finding may provide new insights in elucidating the pathogenesis of HAF.

The effect of treatment with flunixin meglumine at different times relative to hCG administration on ovulation failure and luteal function in mares

Flunixin meglumine (FM), a prostaglandin synthetase inhibitor, causes ovulatory failure in the mare. However, the effect of the FM treatment relative to the time of hCG administration on the ovulation failure has not been determined nor has its effect on the luteal function of treated mares. Estrous mares with a follicle ≥32 mm (range of 32-38 mm) were treated with 1.7 mg/kg b.w. of FM iv at zero, 12, 24 and 36 h (n=6), at 24 and 36 h (n=6), at 28 and 36 h (n=6), at 24h (n=6) or at 30 h (n=6) after treatment with 1500 IU hCG. One group received no FM (control, n=6). Progesterone concentrations were determined using RIA. Mares treated with FM 0-36 h and 24-36 h had higher (P<0.05) incidence of ovulatory failure (83 and 80%, respectively) than mares treated twice at 28 and 36 h, or once at 24 or at 30 h after hCG (16.7, 0 and 0%, respectively). The anovulatory follicles of FM treated mares luteinized and produced progesterone (>2 ng/ml). The progesterone concentration was lower in mares treated with FM at zero to 36 h and at 24-36 h after hCG than in the other groups. In conclusion, the FM administration was effective in blocking ovulation only when the treatment began ≤24 h after hCG and was continued every 12 h until ≥36 h. In addition, the FM-induced anovulatory follicles underwent luteinization of follicular cells with active production of progesterone.

Temporal relationships of the LH surge and ovulation to echotexture and power Doppler signals of blood flow in the wall of the preovulatory follicle in heifers

Changes in echotexture and blood flow in the wall of preovulatory follicles in heifers were studied in relation to the LH surge and ovulation in gonadotrophin-releasing hormone-induced (n = 7; Experiment 1) and spontaneous (n = 8; Experiment 2) ovulators. Ultrasonographic examinations and blood sampling were performed either every hour (Experiment 1) or every 6 h (Experiment 2). The interval from LH peak to ovulation in induced and spontaneous ovulators was 27.1 ± 0.3 and 34.5 ± 1.5 h, respectively. Follicle diameter did not increase between the LH peak and ovulation. In the induced ovulators, serration of the stratum granulosum was detected in one (14%), two (29%), three (43%) and four (57%) heifers at 4, 3, 2 and 1 h before ovulation, respectively. An initial increase in blood flow (P < 0.001) encompassed the LH peak in both experiments. In the induced ovulators, blood flow increased (P < 0.02) to maximum 3 h after the LH peak, maintained a plateau for 5 h, decreased (P < 0.05) between 9 and 14 h, increased (P < 0.05) again between 19 and 21 h and then decreased (P < 0.01) between 25 and 26 h (1 h before ovulation). The biphasic increase and decrease in blood flow and serration of the granulosum in the wall of the preovulatory follicle in cattle are novel findings.