Effect of hCG application at different moments of the estrous cycle on corpus luteum and uterine vascularization and serum progesterone concentration in mares

Abstract

Establishment of pregnancy after embryo transfer is the ultimate goal of an embryo transfer program and increasing pregnancy rates and reducing pregnancy loss are mandatory. The utilization of treatments to improve conception rates in recipient mares has been the focus of several research groups over the last years and the results are controversial. Some studies using human chorionic gonadotrophin (hCG) found promising results. Our hypothesis was that hCG administration would cause an additional stimulation on luteal function, uterine and luteal vascularization and progesterone concentration, and the mares would have increased uterine and cervix tone. Therefore, in the present study the effects of hCG administration to induce ovulation, on day 0 (day of ovulation) or day 5 postovulation were evaluated on corpus luteum characteristics, reproductive tract vascularization, and serum progesterone concentration from ovulation until day 15 postovulation. Groups were: G1: (control)-no hCG; G2: 2500 IU of hCG to induce ovulation when a follicle greater than 35mm and uterine edema were detected; G3: 2500 IU hCG on day 0; G4: 2500 IU hCG on day 5 postovulation. Twelve mares were randomly assigned to each group, during consecutive cycles, in a Latin Square experimental design, in a total of 48 cycles. Doppler ultrasound evaluations were performed daily from day 0 until day 15 postovulation, including mesometrial vascularity, endometrial vascularity and corpus luteum vascularity. Blood samples were collected for serum progesterone concentration. Data was analyzed using the Proc Glimmix SAS Procedure for nonparametric variables and Proc Mixed for parametric parameters. There was no treatment effect for all variables studied (P > 0.05). Characteristics were only affected by day (P < 0.05). It can be concluded that hCG administration at the time points suggested in the current study did not alter the characteristics evaluated.

Assessment of Age Effects on Ovarian Hemodynamics Using Doppler Ultrasound and Progesterone Concentrations in Cycling Spanish Purebred Mares

“…In the current study, Power Doppler allowed us to find significant differences in the follicular and CL vascular perfusion between young and aged mares 5–7 days after ovulation in concordance with Campos [ 8 ]. Our results agree with Bollwein et al [ 4 ], Ginther et al [ 18 ] and Alonso et al [ 19 ], who reported maximum vascularization between 6-days and 8-days post-ovulation. It is well known that luteal vascularization is important in the supply of the nutrients and substrates required for the optimal function and maturity of the CL [ 20 ].…”

“…Although we used hCG treatment for ovulation induction, we did not establish the correlation between that treatment and progesterone concentrations. A study performed by Alonso et al [ 19 ] suggested that hCG treatment did not rise progesterone concentrations.…”

The ovarian and uterine responses of Baixadeiro mares to prostaglandin synchronization during the dry and rainy seasons

“…Changes in tonicity during the reproductive cycle in mares have already been described (Hayes and Ginther, 1986;Cuervo-Arango et al, 2020), as the luteal phase approaches (Griffin et al, 1992;Alonso et al, 2019), with no change occurring during the anovulatory seasonality (Hayes and Ginther, 1986). Also, changes in uterine consistency and texture have been shown to occur gradually throughout estrus (Hayes et al, 1985), characterizing the estrus edema (Moura, 2012).…”

Fertility restoration of racing mare with persistent corpus luteum

“…PCL diagnosis was conducted using behavioral observations, ovarian transrectal palpation, and measurement of P4 concentrations [8]. Mares with PCL have a good tone of the cervix and uterus on transrectal palpation [15], and P4 concentrations of >1.0 ng/mL, indicating luteal activity [16].…”

“…There are few pharmacological methods to improve the function of the CL to sustain the pregnancy of the mares [14]. The progestin injection [21] or human chorionic gonadotropin promised increased pregnancy rates and reduced pregnancy loss [15]. The demerits of this study are that it did not administer the addition of hormones to maintain the pregnancy.…”