Altered gene expression in embryos and endometrium collected on day 8 of induced aluteal cycles in mares

Low progesterone concentration in early pregnancy is detrimental to conceptus development and pregnancy outcome in horses

High progesterone concentrations in the early luteal phase support pregnancy, whereas subphysiological progesterone concentrations delay embryonic development at least until placentation. In this study, fetal growth and development of pregnancy was investigated in pregnancies with prostaglandin F2α-induced low progesterone concentrations (PGF) in the early luteal phase and control pregnancies (CON) in the same mares (n = 12). Mares were inseminated and in PGF pregnancies received the prostaglandin F2α analogue cloprostenol (62.5 µg) on days 0-3 after ovulation to induce subphysiological progesterone concentrations; CON pregnancies remained untreated. Mares were assigned to PGF or CON treatments in alternating order and received the opposite treatment in the following year. Blood was collected and conceptus size determined repeatedly by transrectal (≤day 101) and transabdominal (>day 101) ultrasonography. After birth, foals were weighed, measured and submitted to a clinical examination. Treatment PGF resulted in fewer pregnancies than CON treatment. All foals born from CON pregnancies were healthy and mature, whereas 4/7 PGF pregnancies were either lost (one embryonic death, one abortion) or resulted in the birth of compromised foals (P = 0.018). Size of the conceptus (e.g., diameter day 49: PGF 6.6 ± 0.7, CON 7.7 ± 0.7 cm, P = 0.006) and embryo proper (e.g., crown rump length day 54; PGF 4.4 ± 0.8, CON 5.8 ± 0.6 cm, P = 0.015) differed between treatments. These size differences decreased over time and at birth PGF foals did not differ significantly from CON foals. In conclusion, reduced progesterone concentration in the early luteal phase leads to delayed conceptus growth beyond placentation and increased pregnancy loss.

Relationship between estrus endometrial edema and progesterone production in pregnant mares two weeks after ovulation

BACKGROUND

Progesterone plays a crucial role in the maintenance of pregnancy from conception to about 100-120 days of gestation when placenta becomes the main source of gestagens. The aim of the study was to test progesterone concentration 14 days after ovulation in pregnant mares and relate it to peak estral endometrial edema and the presence of intrauterine fluid (IUF) after artificial insemination (AI), the number of treatments against IUF, and the time from AI to the day when the uterus was found free of fluid.

RESULTS

Mares were divided into two groups: group A (n = 13; age 10.8 ± 4.5 years) in which a normal embryonic vesicle with a diameter ≥ 14 mm and a corpus luteum with a diameter ≥ 15 mm were found 14 days after ovulation, and group B (n = 22; age 9.4 ± 4 .0 years) in which 14 days after ovulation, a small (< 15 mm) corpus luteum and/or a small embryonic vesicle was observed (diameter < 14 mm). Mares from group A had a significantly higher progesterone concentrations at 14 days after ovulation compared with group B mares. The presence of IUF, the number of treatments against IUF, and the time from AI to the day when uterus was found free of fluid did not affect progesterone concentration measured 14 days after ovulation. In group B, a significant correlation was found between progesterone concentration measured 14 days after ovulation and endometrial edema evaluated during estrus.

CONCLUSIONS

In some cases poor development of endometrial edema during estrus can be associated with lower progesterone production 14 days after ovulation. Nevertheless, scientific explanation for this finding cannot be given based on our study.

The correlation of endogenous progesterone concentration in diestrus on early pregnancy rate in Thoroughbred mares

AIM

The aim of this project was to test the hypothesis that progesterone concentration 5 days after ovulation did not differ between pregnant and nonpregnant Thoroughbred mares on stud farms located in the Waikato region of New Zealand.

METHODS

A prospective cohort study was performed involving five stud farms in the Waikato region of New Zealand during the 2018 breeding season. A total of 275 mares were enrolled in the study. Mares were served by 34 individual stallions. Blood samples were taken from each mare 5 days after ovulation (D0) and measured for progesterone concentration. Early pregnancy was confirmed at D14 by transrectal palpation and ultrasonography of the mares reproductive tract.

RESULTS

Progesterone concentration at Day 5 post-ovulation was higher in mares determined to pregnant at Day 14 of gestation than in mares determined to be non-pregnant at Day 14 (6.4 ± 3.0 ng/ml vs 5.5 ± 3.3 ng/ml respectively; P=0.02). A negative association between increasing mare age and pregnancy rate was found but mare age had no effect on progesterone concentration at D5.

CONCLUSIONS

In this study we found that although higher serum progesterone concentration at Day 5 post ovulation was associated with a higher pregnancy rate at Day 14, no predictive or definitive minimum required progesterone concentration could be identified. Additional studies are required to determine if a synthetic progestogens can serve to supplant natural progesterone to increase pregnancy rate in naturally bred mares.

Fertility restoration of racing mare with persistent corpus luteum

Background and Aim:

Persistent corpus luteum (PCL) causes anestrus in mares. This study aimed to determine the effect of intrauterine prostaglandin F2α (PGF2α) treatment on PCL of racing mares to restore fertility.

Materials and Methods:

Twelve racing mares suspected with PCL were diagnosed using transrectal palpation and confirmed by serum progesterone (P4) concentration measurement. PGF2α was infused intrauterine, followed by serum collection at 24, 48, and 72 h after. Estrous symptoms were monitored, and mating was conducted on day 3 of estrus with an earlier injection of 8.4 μg gonadotropin-releasing hormone twice a day. Transrectal palpation was performed on days 21-30 to observe the corpus luteum. Pregnancy diagnosis was performed rectally on 40-45 days post-mating and confirmed using Doppler ultrasound scanning.

Results:

Eleven of the 12 mares had PCL. There was a dramatic reduction in the P4 concentration following PGF2α treatment of mares with PCL. All mares exhibited estrus 2.6±0.55 days post-treatment with a P4 concentration of 0.12±0.12 ng/mL. Rectal palpation and P4 concentration on 21-30 days after estrous onset showed that all mares were ovulating. The evaluation of P4 concentration on days 40-45 post-mating showed that all mares were still in the luteal phase. However, the pregnancy rate was only 54.5% based on rectal palpation and Doppler ultrasound scanning.

Conclusion:

Treatment of PCL in racing mares with an intrauterine infusion of PGF2α restored the estrous cycle and induced ovulation and pregnancy.

Impact of the corpus luteum on survival of the developing embryo and early pregnancy in mares

It has been more than a hundred years that studies aiming to elucidate the processes involved in cyclicity and pregnancy pointed out the requirement of ovaries and corpora lutea for embryo survival and pregnancy establishment. For horses, luteal progesterone is essential for pregnancy only during the first trimester. This progestational support is complex among domestic animals as ovarian luteal function is further enhanced by the LH-action role of equine chorionic gonadotropin (eCG) starting ∼ on Day 35 of pregnancy. Increased eCG secretion leads to the formation of supplementary corpora lutea resulting from follicles that luteinize (accessory corpora lutea) or ovulate (secondary corpora lutea), thus increasing concentrations of blood progesterone. Physiological details of progesterone-driven embryo-maternal interactions continue to be elucidated. In recent years, researchers studying the transcriptomes and secretomes of uterine tubes, endometrium and early embryo provided insight into the composition of molecular and cellular events that enable embryo survival and remodeling of the endometrium before a functional placenta is formed. Aluteal pregnancy models have also shown that while fertilization and early embryo development until the early blastocyst stage can occur under a progesterone-deprived environment, dysregulation of important pregnancy-related genes occur; embryo development is compromised unless progestin supplementation is provided once the embryo arrives into the uterus. As the body of knowledge on embryo-maternal interactions in the horse continues to grow, a fact remains true: luteal support is essential for embryo survival mainly at the uterine stage, driving directly or indirectly gene expression that promotes adequate embryo-maternal physiological interactions until a full competent placenta is formed, resulting in optimal chances of delivering a live foal at term.