Temporal relationships among LH, estradiol, and follicle vascularization preceding the first compared with later ovulations during the year in mares

Doppler Ultrasound in the Reproduction of Mares

Doppler ultrasonographic (US) is a method that provides real-time information on vascular architecture and hemodynamic aspects of blood vessels. It can determine the presence, direction, and speed of blood flow, being subdivided into the categories of color Doppler (color flow and power flow) and pulsed Doppler. The objective of this chapter was to compile data from several studies addressing the use of US Doppler correlated with pathophysiological phenomena of equine reproduction. Initially we decided to describe the technique, advantages, and disadvantages of each Doppler mode. Then the applicability of US Doppler in mares related to equine reproduction. Thus, within this chapter, you will find the form of use and descriptions of studies carried out on vascular perfusion of the follicular dynamics, the corpus luteum, the uterine segments, which we have divided into post-insemination evaluation, endometritis diagnosis and pregnancy diagnosis. So, we hope that this chapter will expand the knowledge about US Doppler and increase the number of veterinarians who will introduce the technique into their practical routine.

Emergence and selection of the dominant follicle and gonadotropin dynamics in postpartum lactating versus non-postpartum cycling mares

Among female livestock, the mare has the shortest interval from parturition to first ovulation. Due to the scarcity of research on postpartum mares, little progress has been made on the characterization of the resumption of ovarian cyclicity after parturition. This study compared follicular and gonadotropin dynamics during follicle emergence and deviation in postpartum lactating (PP Lactating) versus non-postpartum cycling (N-PP Cycling) mares. On the day of parturition, every PP Lactating mare was paired with a N-PP Cycling mare. Comparisons were made by considering the partum-ovulation interval and the postpartum interovulatory interval for the PP Lactating mares, and two interovulatory intervals for the N-PP Cycling mares. The results presented herein demonstrate that during the postpartum period, lactating mares have some similarities in follicular and hormonal profiles around emergence and deviation when compared with non-postpartum cycling mares. However, some peculiar and important characteristics were noticed during the postpartum period in lactating mares: (1) The emergence of the DF occurs around the day of parturition; (2) follicle deviation in the ovulatory wave occurs earlier during the foal heat than in other intervals; (3) lower FSH and LH systemic concentrations were not detrimental enough to prevent the rapid resumption of ovarian activity just after parturition; and (4) the association between parturition and season can have an additional and confounding effect during postpartum ovarian activity in mares. The novel findings of this study provide better knowledge of the resumption of ovarian activity after parturition and may help provide insight into the reproductive management of this species.

Dominant follicle and gonadotropin dynamics before ovulation in postpartum lactating mares

The aim of this study was to compare the dominant follicle (DF) and gonadotropin dynamics for 9 days before ovulation in postpartum lactating (PP Lactating) versus non-postpartum cycling (N-PP Cycling) mares. Every PP Lactating mare on the day of parturition was paired with a N-PP Cycling mare, and the data analyses considered the partum-ovulation interval (POI) and the postpartum interovulatory interval (PPIOI) in PP Lactating mares and two interovulatory intervals in N-PP Cycling mares. The results of the present study revealed several novel and unique aspects of DF development and FSH and LH dynamics before ovulation in PP Lactating mares when compared with N-PP Cycling mares. The most remarkable differences between both groups of mares were the following: (1) a shorter interval to ovulation in PP Lactating mares during the foal heat (POI ≤22 days) compared with all other intervals; (2) a larger DF in PP Lactating mares, and an earlier day of DF at maximum diameter during the foal heat; and (3) lower gonadotropin levels in PP Lactating mares. Regarding the particularities, PP Lactating mares had lower LH levels during the POI than the PPIOI, demonstrating a strong partum effect; spring-foaled mares had longer POIs, larger DF diameters, and lower LH levels; and lower body condition scores and higher body-weight loss led to longer POIs and smaller DF diameters in PP Lactating mares. This study contributes to a broad understanding of ovarian function in the postpartum mare.

Deficiency in proliferative, angiogenic, and LH receptors in the follicle wall: implications of season toward the anovulatory condition

This study aimed to gain insight on the effect of different seasons of the year on the expression pattern of growth factor and hormone receptors involved in follicle development. A novel follicle wall biopsy technique was used to collect in vivo follicle wall layers (ie, granulosa, theca interna, and theca externa) and follicular fluid samples from growing dominant follicles, simultaneously and repeatedly, using the same mares during the spring anovulatory (SAN), spring ovulatory (SOV), summer (SU), and fall ovulatory (FOV) seasons. The immunofluorescent expression patterns of epidermal growth factor receptor (EGFR), Ki-67, vascular endothelial growth factor receptor (VEGFR), and LH receptor (LHR) were evaluated in each follicle wall layer, in addition to intrafollicular estradiol and nitric oxide (NO). Proliferative proteins (EGFR and Ki-67) were highly (P < 0.05-P < 0.001) expressed during the SOV season compared with the SAN and FOV seasons. Lower (P < 0.05-P < 0.001) expression of both proteins was observed during SU compared with the SOV season. The expression of VEGFR was greater (P < 0.05-P < 0.01) in the theca interna of dominant follicles during the SOV season compared with the SAN and SU seasons. Similarly, in the overall quantification, the VEGFR expression was greater (P < 0.001) during the SOV season compared with the SU and FOV seasons. A higher (P < 0.05) LHR expression was detected in the theca interna during the SOV season than the SAN season. Furthermore, a higher (P < 0.05-P < 0.001) expression of LHR was observed in the granulosa, theca interna, and in the overall quantification during the SOV season compared with the SU and FOV seasons. Intrafollicular NO concentration did not differ (P > 0.05) among different seasons of the year. The intrafollicular estradiol concentration was higher (P < 0.05) during the SU compared with the SAN season and higher (P < 0.05) during the FOV season compared with the SAN and SOV seasons. In conclusion, the synergistic effect of lower expression of proliferative protein, angiogenic, and LH receptors in at least some of the layers of the follicle wall seems to trigger dominant follicles toward the anovulation process during the spring and fall transitional seasons.

Seasonal variation in equine follicular fluid proteome

BACKGROUND

Proteomic studies of follicular fluid (FF) exist for several species, including the horse; however, the seasonal influence on FF proteome has not been explored in livestock. The application of high-throughput proteomics of FF in horse has the potential to identify seasonal variations of proteins involved in follicle and oocyte growth.

METHODS

This study (i) profiles the proteomes of equine FF collected from dominant growing follicles during the spring anovulatory season (SAN), and spring (SOV), summer (SUM), and fall (FOV) ovulatory seasons; and (ii) identifies season-dependent regulatory networks and associated key proteins.

RESULTS

Regardless of season, a total of 90 proteins were identified in FF, corresponding to 63, 72, 69, and 78 proteins detected in the SAN, SOV, SUM, and FOV seasons, respectively. Fifty-two proteins were common to all seasons, a total of 13 were unique to either season, and 25 were shared between two seasons or more. Protein-to-protein interaction (PPI) analysis indicated the likely critical roles of plasminogen in the SAN season, the prothrombin/plasminogen combination in SUM, and plasminogen/complement C3 in both SOV and FOV seasons. The apolipoprotein A1 appeared crucial in all seasons. The present findings show that FF proteome of SUM differs from other seasons, with FF having high fluidity (low viscosity).

CONCLUSIONS

The balance between the FF contents in prothrombin, plasminogen, and coagulation factor XII proteins favoring FF fluidity may be crucial at the peak of the ovulatory season (SUM) and may explain the reported lower incidence of hemorrhagic anovulatory follicles during the SUM season.

Estudo da vascularização folicular e do corpo lúteo de éguas cíclicas tratadas com extrato de pituitária equina utilizando ultrassom Doppler colorido

RESUMO Informações sobre a vascularização da parede folicular e do corpo lúteo equino, associadas à superovulação, são escassas. Com o objetivo de avaliar o efeito superovulatório do extrato de pituitária equina (EPE) no fluxo sanguíneo folicular e luteal, foram utilizadas seis éguas Puro Sangue Árabe, em dois ciclos estrais (controle e tratamento). As éguas foram monitoradas diariamente por ultrassonografia modo B, até que os folículos atingissem diâmetro de 23mm (desvio). No ciclo tratamento, as éguas receberam 8mg de EPE, uma vez ao dia, por via IM, até que dois ou mais folículos atingissem o diâmetro entre 32 e 35mm. A ovulação foi induzida com acetato de deslorelina, quando os folículos atingiram, no mínimo, 35mm. No momento do desvio folicular, da indução da ovulação e do último exame pré-ovulatório, foi utilizada a ultrassonografia modo B para medir o diâmetro dos folículos e, no oitavo dia pós-ovulação, para a área do corpo lúteo (CL). Utilizou-se também ultrassonografia com Doppler colorido para avaliar a perfusão sanguínea da parede folicular e do parênquima luteal. No ciclo controle, foi realizado o mesmo procedimento, exceto pelo uso do EPE. Os dados foram submetidos à análise de variância, com nível de significância de 5%. Não foi observado efeito do EPE sobre o número de ovulações, o diâmetro dos folículos, a vascularização da parede folicular e a concentração sérica de estrógeno. Os animais, tratados ou não, apresentaram CLs funcionais, não havendo diferença na área do parênquima ou da vascularização luteal, nem na concentração sérica de progesterona, no oitavo dia após a ovulação. Foi observado que o EPE proporcionou um maior número de folículos subordinados no momento da indução da ovulação do folículo dominante (P ≤ 0,05). Embora esses folículos não tenham chegado a ovular, concluiu-se que o EPE atuou no crescimento de folículos, que podem ser utilizados em outras biotécnicas, como a transferência de oócitos, com maior aproveitamento da reserva folicular de ovários equinos.

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.

Effects of FSH addition to an enriched medium containing insulin and EGF after long-term culture on functionality of equine ovarian biopsy tissue

The effect of FSH supplementation on an enriched cultured medium containing insulin (10 ng/mL) and EGF (50 ng/mL) was investigated on in vitro culture of equine ovarian biopsy tissue. Ovarian tissue fragments were collected from mares (n = 10) and distributed in the following treatments: noncultured control, cultured control, and cultured + FSH. Both treated groups were cultured for 7 or 15 days. The end points evaluated were: follicular morphology, estradiol levels in the culture medium, fluorescence intensity for TUNEL, EGFR and Ki-67 detection, and gene expression of GDF-9, BMP-15, and Cyclin-D2 in the ovarian tissue. After seven days of culture, medium supplemented with FSH had a similar (P > 0.05) percentage of morphologically normal follicles compared to the noncultured control group. Estradiol levels increased (P < 0.05) from Day 7 to Day 15 of culture for both treated groups. No difference (P > 0.05) was observed for TUNEL and EGFR intensity between the noncultured control group and the treated groups after 15 days of culture. Ki-67 intensity did not differ (P > 0.05) between treated groups after 15 days of culture, but decreased (P < 0.05) when compared with the noncultured control group. Similar (P > 0.05) mRNA expression for GDF-9, BMP-15, and Cyclin-D2 was observed among all treatments after 15 days of culture. In conclusion, an enriched medium supplemented or not with FSH was able to maintain the functionality of equine ovarian biopsy tissue after a long-term in vitro culture.

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.

Reproductive performance of donor mares subsequent to eFSH treatment in early vernal transition: Comparison between the first, second, and mid-season estrous cycles of the breeding season

The objective was to compare the reproductive performances associated with the first (Cycle-1), second (Cycle-2), and mid-season (MS-Cycle) ovulations of the breeding season in donor mares that were treated with equine-FSH (eFSH) in the early vernal transition. Mares (n=15) kept under ambient light were examined ultrasonographically per-rectum starting January 30. When an ovarian follicle > or =25mm in diameter was detected, twice daily eFSH treatments were initiated. The eFSH treatments ceased when a follicle > or =35mm was detected, and 36h later hCG was administered. Thereafter, mares were artificially inseminated every 48h until ovulation (Day 0). Trans-cervical embryo recovery attempts were performed on Day 8, and subsequently PGF2alpha was administered. Equine FSH was not administered in the subsequent estrous cycles. In Cycle-2 and in the MS-Cycle, hCG was administered when a follicle > or =35mm was detected; breeding, embryo recovery, and PGF2alpha administration, were similar to Cycle-1. Mares had an untreated estrous cycle (no treatment or breeding) between Cycle-2 and the MS-Cycle. All mares developed follicle(s) > or =35mm after 4.9+/-0.6 days of eFSH treatment, and subsequently ovulations occurred; mean (95% CI) interval from treatment initiation to ovulation was 7.9 (6.5-9.3) days. The number of preovulatory follicles (> or =30mm) at the time of hCG administration (Cycle-1: 2.2+/-0.3 compared with Cycle-2: 1.0+/-0 compared with MS-Cycle: 1.1+/-0.1 follicles), and the number of ovulations (2.5+/-0.4 compared with 1.0+/-0 compared with 1.1+/-0.1 ovulations) were greater (p<0.05) in Cycle-1. Nevertheless, mean embryo numbers did not differ among cycles (0.8+/-0.2 compared with 0.5+/-0.1 compared with 0.5+/-0.1 embryo/mare). On average, embryo morphology grade was less (p<0.05) in Cycle-1 as compared to non-eFSH cycles (combined Cycle-2 and MS-Cycle). This impaired embryo quality could be due to a seasonal effect, or negative effect of the eFSH treatment, which was possibly related to alterations in the hormonal environment (estradiol-17beta and progesterone). A prolonged IOI (>21 days) was recorded in 7 of 15 mares following the Cycle-1 ovulation, but not subsequently. In conclusion, eFSH treatment of vernal transitional donor mares stimulated ovulation within only few days of treatment, and the following embryo recovery rate was at least as good as in the subsequent estrous cycles; however, on average, embryos were morphologically impaired. In subsequent estrous cycles in the breeding season, ovulations, embryo recovery rates, and embryo variables did not appear to be negatively affected; however, the first inter-ovulatory interval of the breeding season was prolonged in approximately half of the mares.

Follicle development in mares

The mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or to regress) at any given stage of follicular wave development. Periodic development of follicular waves continuously occurs during most of post-natal life in the mare and is influenced by factors such as stage of oestrous cycle, season, pregnancy, age, breed and individual so that different types of follicular waves (minor or major, ovulatory or anovulatory) and different levels of activity within waves may develop under different physiological conditions. Changes in gonadotropin levels and/or in the sensitivity of follicles to circulating gonadotropins seem to account largely for these physiological variations in follicle development.