Dynamics of the Equine Preovulatory Follicle and Periovulatory Hormones: What's New?

Cervix-Deep Rectal Temperature Differential on the Day of Ovulation is Correlated With Embryo Recovery Results in Mares

Variations in temperature throughout the reproductive tract have been noted in many species. A recent study found the cervix-rectum temperature differential (CR-TD) in cattle was related to fertility. The present study aimed to assess the CR-TD in mares around the time of ovulation and relate it to embryo recover. Over 52 cycles, mares were inseminated with a fertile stallion and embryo recovery was undertaken on Day 7 post ovulation. Further 10 control mares were not inseminated. Rectal and cervical temperatures were measured using a precision thermometer on four or five occasions: the day of deslorelin administration and insemination, the day before ovulation, the day of ovulation (Day 0), the day after ovulation and, for inseminated mares, before embryo recovery on Day 7. One-way ANOVA showed that the CR-TD was significantly lower on the day of ovulation in the 36 positive cycles, in which an embryo was recovered, versus the 16 in which the embryo flush was negative (0.21 ± 0.17 vs. 0.40 ± 0.09°C; p < 0.001). Control cycles showed equivalent CR-TD to positive (0.13 ± 0.22 vs. 0.21 ± 0.17°C; p = 0.196) but not negative cycles (0.13 ± 0.22 vs. 0.40 ± 0.09°C; p < 0.001). A positive embryo recovery was associated with lower CR-TDs from the time of insemination and deslorelin to the day after ovulation compared to the day of embryo flushing (RM ANOVA; p < 0.001; Pairwise comparisons; p ≤ 0.01, in all cases). Rectal or cervical temperatures per se showed no significant differences between positive, negative or control cycles at any time point. In conclusion, a thermoregulatory process occurs close to ovulation which results in a lower CR-TD in cycles that produced an embryo versus those which did not. Further characterisation of TDs within the reproductive tract of the mare would increase our understanding of the conditions required for optimum fertility.

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.

Follicle Selection in Mares as a Model for Illustrating the Many Hormonal and Biochemical Interactions That Drive a Single Physiological Mechanism

The mechanism for selection of the future dominant or ovulatory follicle in mares involves a relatively abrupt separation in growth rates between the future dominant follicle and several subordinate follicles and is termed diameter deviation. The event is used to illustrate that a coordinated complex of many follicular, hormonal, and biochemical factors interact and interbalance during a single physiological mechanism. For example, a positive effect of follicle stimulating hormone (FSH) on development of all follicles during the growing phase can later involve a positive effect of luteinizing hormone (LH) but apparently only on the future dominant follicle. In turn, the developing and future dominant follicle produces estradiol which at appropriate times and degrees reduces FSH concentrations to accommodate follicle functions at certain levels of FSH. Meanwhile, the estradiol prevents LH from increasing from a useful to an adverse concentration. These interactions enmesh with the production and roles of other factors (e.g., inhibin, insulin-like growth factor) during follicle selection. The wide array of morphological, hormonal, and biochemical activities occur in harmony even when in the same tissue and often at the same time.

Follicular-fluid proteomics during equine follicle development

The complex composition of the follicular fluid (FF), the intimate proximity to the oocyte, and the continual changes in their composition have a major effect on folliculogenesis and oogenesis. To date, the profiling of FF proteomes during follicle selection, development, and ovulation has not been comprehensively investigated. Therefore, a shotgun proteomics approach and bioinformatics analyses were used to profile the proteomes of equine FF harvested in vivo from follicles at the following development stages: predeviation (18-20 mm), deviation (22-25 mm), postdeviation (26-29 mm), preovulatory (30-35 mm), and impending ovulation. A total of 294 proteins were detected in FF (FDR <1%), corresponding to 65 common proteins and 124, 142, 167, 132, and 142 proteins in the predeviation, deviation, postdeviation, preovulatory, and impending ovulation groups, respectively. The higher expression of properdin and several other proteins belonging to the complement system during the deviation time and ovulation suggested their contribution in the selection of the future dominant follicle and ovulation. Apolipoprotein A-1 and antithrombin-III appeared to be important throughout folliculogenesis. The "complement and coagulation cascades" was the major KEGG pathway across all stages of follicle development. The significant expression of several proteins belonging to the serine-type endopeptidase indicated their likely contribution to follicle and oocyte development. Our data provide an extensive description and functional analyses of the equine FF proteome during follicle selection, development, and ovulation. This information will help improve understanding of the ovarian function and ovulatory dysfunctions and might serve as a reference for future biomarker discovery for oocyte quality assessment.

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.

Influência da somatotropina recombinante bovina no desenvolvimento folicular e na coleta de embriões em éguas

RESUMO Dez éguas, sem raça definida, foram submetidas a avaliações ultrassonográficas durante o intervalo interovulatório, avaliando-se folículos ≥ 5mm. Cinco éguas foram tratadas com 500mg de r-bST no primeiro e no 14º dia pós-ovulação (grupo GT), e as demais com soro fisiológico (grupo GC). Quando o folículo dominante atingiu diâmetro ≥ 40mm, foram induzidas com hCG e inseminadas 24 horas após, sendo submetidas à coleta de embrião seis dias após a ovulação. Os dados foram agrupados de acordo com o diâmetro do folículo dominante nas fases de emergência, divergência, dominância, pré-ovulatória, indução, inseminação e ovulação. Todas as éguas foram usadas duas vezes, no mesmo grupo. O GT apresentou crescimento folicular precoce para as fases de emergência, divergência, dominância e pré-ovulatória, assim como para o seu maior folículo subordinado, que cresceu mais cedo. As taxas de recuperação foram de 90% (GC) e 70% (GT), em 16 estruturas coletadas, obtendo-se uma não fecundada e um blastocisto inicial para o grupo GC; os demais, no estágio de mórula, apresentaram comportamento semelhante entre os grupos. Conclui-se que a r-bST influencia a dinâmica folicular de éguas, levando a uma antecipação do desenvolvimento folicular, que pode ser utilizada para encurtar o ciclo estral.

Can the Presence of Ovarian Corpus Luteum Modify the Hormonal Composition of Follicular Fluid in Mares?

The hypothesis of this study was to investigate if the presence of corpus luteum (CL) in one ovary could modify the hormonal content of follicular fluid (FF) in the follicles. Sixty ovaries were taken after the slaughter of 30 clinically healthy mares. In relation to the sizes, the follicles were classified into three different categories, as small (20-30 mm), medium (31-40 mm) and large (≥41 mm). Blood samples were collected from the jugular vein of mares before their slaughter, and then the FF samplings were extracted from each single follicle. The ovaries that were collected were classified into two groups, according to the presence (CL-bearing) or absence (non-CL-bearing) of CL. The serum and FF samples were analysed for progesterone (P4), oestradiol-17β (E2), testosterone (T), androstenedione (A4) and dehydroepiandrosterone (DHEA). Intrafollicular P4 concentrations in large follicles of CL-bearing groups were lower than for non-CL-bearing ones. Intrafollicular E2 concentrations increased with the increase of the follicle diameter in both groups, CL-bearing and non-CL-bearing. However, in the FF with a large and medium follicle size, E2 concentrations were significantly higher in non-CL-bearing groups than in CL-bearing groups. T and A4 significantly increased in the large and medium follicle sizes when compared to the small follicle sizes in both groups, but higher concentrations in the non-CL-bearing group were obtained. Intrafollicular DHEA significantly decreased with the increase of the follicular diameter in both groups. Steroid hormones in FF dynamically changed, according to the presence or not of CL in the ovary. This study brings new knowledge on the role of the CL in the follicular hormonal composition in mares.

Intrafollicular and systemic serotonin, oestradiol and progesterone concentrations in cycling mares

The hypothesis that a local serotonergic network might also exist in the follicle of mares remains poorly documented, with exception for humans and laboratory species. For this reason, the aim of the present study was to clarify this possibility, investigating intrafollicular serotonin concentrations of the cycling mare at ovulation time. Sixty ovaries collected from 30 clinically healthy mares of slaughterhouse meat production with clinically normal reproductive tracts after slaughtering were evaluated. Blood samples were taken prior to sacrifice. Follicles were classified in three categories in relation to size, as small (20-30 mm), medium (31-40 mm) and large (>41 mm), and the follicular fluid samples were extracted from each follicle. Intrafollicular and systemic serotonin (5-HT), oestradiol-17β (E₂ ) and progesterone (P₄ ) were determined by means of enzyme-linked immunosorbent assay and RIA, respectively. Intrafollicular 5-HT, E₂ and P₄ concentrations were higher than systemic ones (p < .05). 5-HT concentrations increased in larger compared to medium follicles, without differences compared to small size follicles (p < .05). 5-HT and E₂ (r = .79) and 5-HT and P₄ (r = .79; p < .05) were positively correlated. 5-HT and P₄ concentrations in follicular fluid increased progressively with the increase in follicular size (p < .05). Follicle diameter and E₂ (r = .85) and P₄ (r = .68) were correlated (p < .05). Since serotonin interacts with steroids, its role on steroidogenesis during growth of the dominant follicle may be suggested.

Effect of breed and other animal-related factors on conception rate to artificial insemination with frozen semen in mares in Ethiopia

Equine reproduction is unique by having long behavioral estrus and differences in time of breeding between breeds and individuals of mares. An experimental study was conducted at the Balderas Sport Horses and Recreational Center, Addis Ababa, Ethiopia, from January to June, 2018, to evaluate conception rate to frozen semen in local and exotic crossbreed mares. Mares were teased to characterize estrus behavior and examined by ultrasound in determining imminent ovulation. Inseminations were done post ovulation within an average of 6-9 h using frozen-thawed semen. The overall conception rate to frozen semen was 15/21 (71.43%) with 8/11 (72.73%) in crossbreed and 7/10 (70%) in local breed mares. Age and body condition score (BCS) of animals had no significant effect on conception rate to AI with frozen semen. A slightly higher conception rate was obtained when ovulation was from the right ovary than when ovulated from the left ovary. A higher conception rate was obtained when the diameter of the preovulatory follicle was ≤ 45 mm than above diameter. The conception rate increased significantly with increased number of services/conception with an overall mean ± (SEM) of 2.2 ± 0.2 services/conception. A more number of services/conception were required for local breed (2.7 ± 0.2) than crossbreed mares (1.8 ± 0.3) and again for lower body condition scores than higher condition scores of mares. In conclusion, the increased number of services improved the conception rate with significant difference between breed of mares, whereas good management of mares for improved body conditions could be required to decrease the number of services per conception.

SUPEROVULAÇÃO EM ÉGUAS DA RAÇA CRIOULA E QUARTO DE MILHA COM EXTRATO DE PITUITÁRIA EQUINA (EPE)

Resumo Este trabalho compara a resposta superovulatória de éguas doadoras de embriões das raças Quarto de Milha (QM) e Crioula, utilizando um protocolo com baixa dose de extrato de pituitária equina (EPE). Oito éguas QM e seis éguas Crioulas foram acompanhadas durante 3 ciclos estrais consecutivos, sendo que cada ciclo corresponde a um grupo. Grupo Controle – monitoramento do crescimento folicular até a ovulação; Grupo EPE – monitoramento ultrassonográfico até que os folículos atingissem cerca de 20 mm de diâmetro e, posteriormente, administração de 7 mg de EPE, duas vezes ao dia, até a indução da ovulação com 2500UI de hCG; Grupo Pós-EPE – idem ao grupo controle. Os dados foram submetidos à análise de variância, utilizando o procedimento GLM do pacote estatístico SAS, sendo previamente testadas para normalidade dos resíduos, e as médias comparadas pelo teste de Tukey ao nível de 5%. Nas éguas Crioulas tratadas com EPE houve um aumento no número de ovulações (p=0,0534), com média de 3,33±2,06 quando comparadas aos grupos controle e pós-EPE e às éguas da raça QM (2,00±0,53). O tratamento com EPE na dose preconizada permitiu uma melhor resposta superovulatória e produção embrionária nas éguas Crioulas, quando comparadas com as éguas Quarto de Milha.

In vivo antral follicle wall biopsy: a new research technique to study ovarian function at the cellular and molecular levels

BACKGROUND

In vivo studies involving molecular markers of the follicle wall associated with follicular fluid (FF) milieu are crucial for a better understanding of follicle dynamics. The inability to obtain in vivo samples of antral follicle wall (granulosa and theca cells) without jeopardizing ovarian function has restricted advancement in knowledge of folliculogenesis in several species. The purpose of this study in mares was to develop and validate a novel, minimally invasive in vivo technique for simultaneous collection of follicle wall biopsy (FWB) and FF samples, and repeated collection from the same individual, during different stages of antral follicle development. We hypothesized that the in vivo FWB technique provides samples that maintain the normal histological tissue structure of the follicle wall layers, offers sufficient material for various cellular and molecular techniques, and allows simultaneous retrieval of FF.

METHODS

In Experiment 1 (ex vivo), each follicle was sampled using two techniques: biopsy forceps and scalpel blade (control). In Experiment 2 (in vivo), FWB and FF samples from 10-, 20-, and 30-mm follicles were repeatedly and simultaneously obtained through transvaginal ultrasound-guided technique.

RESULTS

In Experiment 1, the thickness of granulosa, theca interna, and theca externa layers was not influenced (P > 0.05) by the harvesting techniques. In Experiment 2, the overall recovery rates of FWB and FF samples were 97 and 100%, respectively. However, the success rate of obtaining samples with all layers of the follicle wall and clear FF varied according to follicle size. The expression of luteinizing hormone receptor (LHR) was mostly confined in the theca interna layer, with the estradiol-related receptor alpha (ERRα) in the granulosa and theca interna layers. The 30-mm follicle group had greater (P < 0.05) LHR expression in the theca interna and ERRα in the granulosa layer compared to the other groups. The overall expression of LHR and ERRα, and the intrafollicular estradiol were higher (P < 0.05 - P < 0.0001) in the 30-mm follicle group.

CONCLUSION

The in vivo technique developed in this study can be repeatedly and simultaneously used to provide sufficient FWB and FF samples for various cellular and molecular studies without jeopardizing the ovarian function, and has the potential to be translated to other species, including humans.

Impact of Equine and Bovine Oocyte Maturation in Follicular Fluid From Young and Old Mares on Embryo Production in Vitro

Equine follicular fluid (FF) provides autocrine and paracrine factors from theca, granulosa, and cumulus cells, both reflecting and impacting oocyte and follicle maturation. We hypothesized that maturation of oocytes in FF from old versus young mares has a deleterious effect on oocyte maturation and their subsequent developmental potential. Follicular fluid was collected from the large, dominant follicle from young mares (4-13 years) or old mares (21-26 years) and classified as: (1) Noninduced follicular fluid (NFF), FF from noninduced follicle 33 ± 3 mm, or (2) Induced follicular fluid (IFF), FF collected ∼24 hours after administration of ovulation-inducing drugs when a follicle 33 ± 3 mm was observed. In experiment 1, immature equine oocytes were collected, matured in vitro for 30 ± 2 hours in 100% IFF, collected from young or old mares, with the addition of follicle stimulating hormone (5 mU/mL), then fertilized by intracytoplasmic sperm injection. In experiment 2, immature bovine oocytes were collected, matured in 100% IFF or NFF, collected from young mares or old mares, then fertilized via in vitro fertilization. In experiment 1, more blastocysts tended (P = .08) to be produced from equine oocytes that were matured in old versus young mare FF. In experiment 2, when IFF and NFF groups were combined, cleavage rates were higher (P = .001) when bovine oocytes were matured in FF from young than old mares. In contrast to our hypothesis, we observed no conclusive evidence that FF from old mares has a deleterious impact on oocytes and their early developmental potential.

Pre-ovulatory follicle affects corpus luteum diameter, blood flow, and progesterone production in mares

Color Doppler ultrasonography was used to study the temporal relationships between pre-ovulatory follicle (POF) and corpus luteum (CL) diameter and blood flow, with systemic progesterone (P4) concentration during two transitional ovulatory seasons in mares. Variables of POF and CL/P4 were evaluated for 6days before and 17days after ovulation, respectively. Evaluations were performed during two consecutive estrous cycles in spring and fall seasons, and during the last estrous cycle of the season. There were significant correlations among POF and CL variables, and P4 concentration that ranged from 0.24 to 0.95, and among the ratios of different variables that ranged from 0.39 to 0.92. There were linear regressions (P<0.01-0.001) for all comparisons among different variables. The POF diameter before the first ovulation of the season was larger (P<0.05), and POF vascularity was less (P<0.05), than in the last estrous cycle during the season. The CL blood flow was less (P<0.01) during the last compared with first pre-ovulatory period of the season. The POF diameters were positively correlated (r=0.67) during the two pre-ovulatory periods of spring and fall. Results provide evidence that the POF affects CL diameter and blood flow, and subsequently P4 production, and that POF diameter is repeatable within the same individual during different seasons.

Seasonal or pathological findings? Morphofunctional characteristics of the equine endometrium during the autumn and spring transition

The deep anoestrous phase in winter is part of the anovulatory season in mares and is bordered by the autumn and spring transitional periods (ATP/STP). To define an annual time span for effective prognostic biopsy sampling, the aim of this study was to provide a morphofunctional characterization of the endometrium during ATP and STP. To outline both transitional periods, endometrial specimens were taken in September, October and November (n = 76) as well as February, March and April (n = 184) with the requirement of a detailed clinical documentation. Tissue samples were examined histologically with special emphasis on the functional endometrial morphology. Additionally, an immunohistochemical evaluation was performed on selected specimens regarding the expression of oestrogen receptor α, progesterone receptor and Ki67-antigen. An absent to low endometrial activity was ascertained in more than 60% of all specimens from late October onwards, whereas a comparably lacking or low activity in STP was observed until early April. Approximately 30% (ATP) to 22% (STP) of all samples exhibited a predominantly "irregular" endometrial differentiation. During the transitional periods, the clinically evaluated ovarian status (transrectal palpation, transrectal ultrasonography and/or serum progesterone and oestrogen analyses) and the endometrial functional morphology were in accordance with approximately 70% of all cases. The expression of steroid hormone receptors and Ki67-antigen was generally low. Given that endometrial maldifferentiations were frequently found during ATP and STP, its occurence might display a characteristic and physiological feature of the transitional periods. Regarding the functional endometrial morphology, a diagnostic biopsy sampling should therefore be performed between late April and before September.

Why doesn't conventional IVF work in the horse? The equine oviduct as a microenvironment for capacitation/fertilization

In contrast to man and many other mammalian species, conventional in vitro fertilization (IVF) with horse gametes is not reliably successful. The apparent inability of stallion spermatozoa to penetrate the zona pellucida in vitro is most likely due to incomplete activation of spermatozoa (capacitation) because of inadequate capacitating or fertilizing media. In vivo, the oviduct and its secretions provide a microenvironment that does reliably support and regulate interaction between the gametes. This review focuses on equine sperm-oviduct interaction. Equine sperm-oviduct binding appears to be more complex than the presumed species-specific calcium-dependent lectin binding phenomenon; unfortunately, the nature of the interaction is not understood. Various capacitation-related events are induced to regulate sperm release from the oviduct epithelium and most data suggest that exposure to oviduct secretions triggers sperm capacitation in vivo However, only limited information is available about equine oviduct secreted factors, and few have been identified. Another aspect of equine oviduct physiology relevant to capacitation is acid-base balance. In vitro, it has been demonstrated that stallion spermatozoa show tail-associated protein tyrosine phosphorylation after binding to oviduct epithelial cells containing alkaline secretory granules. In response to alkaline follicular fluid preparations (pH 7.9), stallion spermatozoa also show tail-associated protein tyrosine phosphorylation, hyperactivated motility and (limited) release from oviduct epithelial binding. However, these 'capacitating conditions' are not able to induce the acrosome reaction and fertilization. In conclusion, developing a defined capacitating medium to support successful equine IVF will depend on identifying as yet uncharacterized capacitation triggers present in the oviduct.

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.

Accessory corpora lutea formation in pregnant Hokkaido sika deer (Cervus nippon yesoensis) investigated by examination of ovarian dynamics and steroid hormone concentrations

Generally, sika deer conceive a single fetus, but approximately 80% of pregnant females have two corpora lutea (CLs). The function of the accessory CL (ACL) is unknown; moreover, the process of ACL formation is unclear, and understanding this is necessary to know its role. To elucidate the process of ACL formation, the ovarian dynamics of six adult Hokkaido sika deer females were examined ultrasonographically together with peripheral estradiol-17β and progesterone concentrations. ACLs formed in three females that conceived at the first estrus of the breeding season, but not in those females that conceived at the second estrus. After copulation, postconception ovulation of the dominant follicle of the first wave is induced by an increase in estradiol-17β, which leads to formation of an ACL. A relatively low concentration of progesterone after the first estrus of the breeding season is considered to be responsible for the increase in estradiol-17β after copulation.

Characterization of the estrous cycle of Asinina de Miranda jennies (Equus asinus)

This study aims to characterize the estrous cycle of Asinina de Miranda jennies in the breeding season, on the basis of data collected from serial ultrasonographic examination and serum progesterone determinations in 14 females during a total of 33 cycles. The length of the interovulatory interval was 23.8 ± 0.55 days, the diestrus and estrus lasting 17.9 ± 0.46 days and 6.65 ± 0.30 days, respectively. Age and body condition score (BCS) affected the length of the interovulatory intervals; BCS also influenced the diestrus length and the time in heat after ovulation (P > 0.05). The incidence of single, double, and triple ovulations was 57.58%, 36.36%, and 6.06%, respectively. Multiple ovulations affected neither the length of the interovulatory interval nor the individual cycle stages (P > 0.05) but lengthened the interval from the beginning of estrus to the last ovulation (P = 0.01). When combined with age, higher BCS affected the ovulation rate (P = 0.001). Deviation of the dominant follicle occurred around Day 8.7 (Day 0 = ovulation) when both single and multiple ovulations were considered. The dominant follicle was larger at divergence in single ovulators (19.18 ± 0.97 mm) compared with that in multiple ovulators (18.05 ± 1.16 mm). The overall maximum follicular diameter before ovulation was smaller in multiple ovulatory cycles than that in single ovulatory cycles (37.2 ± 0.83 mm vs. 40.2 ± 1.41 mm, respectively; P = 0.03). The daily growth rate of dominant follicles was independent of the ovulation rate (P > 0.05) for the intervals before and after the estrus onset. The dominant follicle size and the follicle growth rates were independent of BCS (P > 0.05). Data collected in this study revealed resemblances between Mirandese and other Iberian and Brazilian breeds with regard to estrous cycle characteristics.

How ultrasound technologies have expanded and revolutionized research in reproduction in large animals

Gray-scale ultrasonic imaging (UI) was introduced in 1980 and initially was used to examine clinically the reproductive tract of mares. By 1983 in mares and 1984 in heifers/cows, UI had become a tool for basic research. In each species, transrectal gray-scale UI has been used extensively to characterize follicle dynamics and investigate the gonadotropic control and hormonal role of the follicles. However, the use of transrectal UI has also disclosed and characterized many other aspects of reproduction in each species, including (1) endometrial echotexture as a biological indicator of circulating estradiol concentrations, (2) relative location of the genital tubercle for fetal gender diagnosis by Days 50 to 60, and (3) timing of follicle evacuation during ovulation. Discoveries in mares include (1) embryo mobility wherein the spherical conceptus (6-16 mm) travels to all parts of the uterus on Days 11 to 15, (2) how one embryo of a twin set eliminates the other without self-inflicted damage, and (3) serration of the granulosum of the preovulatory follicle opposite to the future rupture site as an indicator of imminent ovulation. Studies with color-Doppler UI have shown that vascular perfusion of the endometrium follows the equine embryo back and forth between uterine horns and follows the expansion of the bovine allantochorion throughout each horn. In heifers, blood flow in the CL increases during the ascending portion of an individual pulse of PGF2α metabolite and then decreases. These examples highlight the power of UI in reproduction research. Without UI, it is likely that these and many other findings would still be unknown.

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.