Effects of Repeated Embryo Collection on Embryo Recovery Rate in Fertile Mares

Effects of repeated embryo flushing without PGF2α administration on luteal function, percentage of unwanted pregnancy and subsequent fertility in mares

BACKGROUND

PGF2α is commonly given at the end of embryo flushing (EF) to shorten the interval to the next oestrus and ovulation.

OBJECTIVES

To determine the effect of repeated EF on plasma progesterone concentration, percentage of mares with endometritis, unwanted pregnancy and subsequent fertility in mares flushed without the use of PGF2α.

STUDY DESIGN

Controlled experiments.

METHODS

Nine mares were inseminated in seven consecutive cycles (n = 63), to either perform an EF (n = 54) 7-9 days after ovulation or left pregnant (n = 9). PGF2α was not used to induce oestrus. Ultrasound examination and blood sampling were performed just before the EF and 72 h later to determine changes in progesterone concentration and signs of endometritis.

RESULTS

The overall percentage of positive EF/pregnancy was 55.5% (30/54) and 66.7% (6/9), respectively. The likelihood of pregnancy/positive EF in the first three cycles was 55.5% (15/29). This was not different (p > 0.1) from the fertility of the last four cycles (69.4%, 25/36). In five EF cycles (9.3%), mares had signs of endometritis and early luteolysis (progesterone <2 ng/mL) 72 h after EF. The reduction in progesterone concentration by 72 h after EF was greater (p < 0.05) for Day 9 (-2.3 ± 0.7 ng/mL) than Day 7 (-1.0 ± 0.8 ng/mL) or Day 8 (-1.3 ± 1.1 ng/mL) cycles. The progesterone concentration in non-flushed mares did not vary significantly during the sampled period (Day 7-12). There were 5 cycles in which the donor mare remained pregnant after the EF, although four were from a single mare.

MAIN LIMITATIONS

The mare population was limited to barren and maiden mares. The cycle order and operator allocation to each EF were not randomised.

CONCLUSIONS

EF induces a subtle, but significant reduction in progesterone concentrations compared with non-EF cycles. However, the percentage of mares with EF-induced full luteolysis is low (9.3%). The fertility of mares after repeated EF without administration of PGF2α was unaffected; however, there is a considerable risk of unwanted pregnancy (5/27 = 18.5%) in donors from which an embryo was not recovered.

Embryo survival in the oviduct not significantly influenced by major histocompatibility complex social signaling in the horse

The major histocompatibility complex (MHC) influences sexual selection in various vertebrates. Recently, MHC-linked social signaling was also shown to influence female fertility in horses (Equus caballus) diagnosed 17 days after fertilization. However, it remained unclear at which stage the pregnancy was terminated. Here we test if MHC-linked cryptic female choice in horses happens during the first days of pregnancy, i.e., until shortly after embryonic entrance into the uterus and before fixation in the endometrium. We exposed estrous mares to one of several unrelated stallions, instrumentally inseminated them with semen of another stallion, and flushed the uterus 8 days later to test for the presence of embryos. In total 68 embryos could be collected from 97 experimental trials. This success rate of 70.1% was significantly different from the mean pregnancy rate of 45.7% observed 17 days after fertilization using the same experimental protocol but without embryo flushing. Embryo recovery rate was not significantly dependent on whether the mares had been socially exposed to an MHC-dissimilar or an MHC-similar stallion. These observations suggest that MHC-linked maternal strategies affect embryo survival mainly (or only) during the time of fixation in the uterus.

Evaluation of environmental effects on reproductive characteristics of Mangalarga Marchador mares in a commercial embryo transfer program

The objective of this study was to evaluate the environmental effects on embryo recovery rate and pregnancy rate of Mangalarga Marchador mares. The reproductive characteristics of donor and recipient mares were evaluated during five years in Brazilian tropical environment. The mares were used throughout the year and seasons were classified as: October to April (breeding season - BS); May (autumn transition out of the breeding season - ATBS); June to August (non-breeding season - nBS); and September (vernal transition into the breeding season - VTBS). Daily temperature rainfall and hours of daylight (photoperiod) were measured during all months and years of evaluation. The embryo recovery rate (ERR) and the pregnancy rate (PR) were observed and frequencies were calculated. The effect of environmental variables, day of flushing, and hormonal treatments (estradiol benzoate and progesterone) were determined for the reproductive measures using the Chi-square and Kruskal-Wallis tests. Significant effects were noted of the year, season and temperature on ERR (P < 0.05), but no significant effects were observed of the environmental parameters (year, season, hormone treatment, rainfall and photoperiod) on PR (P > 0.05). The day of uterine flush affected ERR (P < 0.05) but did not affect PR (P > 0.05). In addition, hormone treatment also supported favorable results of PR in recipient mares during nBS. The conclusion is that mares of this breed can be used in reproduction all year long, with good pregnancy rates, in Brazil's tropical environment. The hormone treatment also supported favorable pregnancy rates in recipient mares during the non-breeding season. It seems that mares can have good pregnancy rates throughout the year in Brazil´s tropical environment.

Embryo transfer in competition horses: Managing mares and expectations

Embryo transfer (ET) is an accepted and successful technique for obtaining foals from mares without interrupting their competition careers. Recent research, however, suggests that the potential of factors including heat, exercise, repeated embryo flushing and repeated manipulation of the reproductive cycle using exogenous hormones to have a negative impact on fertility may have been underestimated. This paper reviews the evidence base for involvement of these factors in repeated failures to recover embryos from nongeriatric competition mares without obvious clinical or pathological indications of reproductive abnormalities. It concludes that, for some mares at least, a cessation of exercise for the periovulatory period and the period between ovulation and embryo flushing, combined with careful management of flushing-induced endometritis, and minimal hormonal manipulation of the reproductive cycle, may be necessary to optimise embryo recovery rates. Mare owners may have been encouraged to request ET for their mares following high-profile examples in the media of elite mares that have produced foals by ET whilst competing. The veterinarian should educate mare owners about the multiple factors that may affect the chances of recovering an embryo from their mares, and should manage the expectations of mare owners so that they do not approach ET programmes in the expectation that there will be no disruption to their training and competition plans.

Increasing expression of oxytocin and vasopressin receptors in the equine conceptus between Days 10 and 16 of pregnancy

Oxytocin (OT) and arginine vasopressin (AVP) have been detected in the yolk sac of the pre-attachment equine conceptus. Therefore, we have assessed the presence of OT and AVP receptors in equine conceptuses between Days 10 and 16 of pregnancy by qualitative PCR, quantitative PCR and immunohistochemistry. Expression of OT receptor and of the AVP receptors V1aR and V2R could be verified after sequencing the RT-PCR products of the expected length. The size of conceptuses used for quantitative PCR significantly increased with day of pregnancy (P<0.01) as did their quantitative expression of OTR (P<0.01). Immunohistochemistry of OTR resulted in weak trophectodermal abundance on Day 10, increasing at Day 12. On Day 14, staining intensity increased in individual cells of the trophectoderm while it decreased in other cells; this trend became more apparent on Day 16. The endoderm of the trophoblast and surrounding subtrophoblastic compartments always showed moderate staining for OTR. On Day 10 immunoreactive V2R protein was localised in the trophectodermal apical membrane; on Day 12 it was also present in the basal membrane and weakly in the cytoplasm. On Day 14 only individual trophectodermal cells showed positive supranuclear cytoplasmic areas or V2R, whereas on Day 16 about one-third of the trophectodermal cells were stained entirely and intensely positive. These results suggest an involvement of OT and AVP action in the development and expansion of the early equine conceptus.

Sex-dependent insulin like growth factor-1 expression in preattachment equine embryos

An adjustment of sex ratio of offspring to the conditions present at conception is seen in many mammals including horses. This depends on preferential survival of male embryos under conditions of high energy intake. In several species, growth factors including insulin like growth factor (IGF)-1 have been shown to promote embryonic development by decreasing apoptosis and increasing cell proliferation. We hypothesized that sex-related differences in IGF-1 expression in equine embryos during the phase of maternal recognition of pregnancy might exist and thus contribute to preferential survival of embryos from either of both sexes under specific environmental conditions. Insulin like growth factor-1 mRNA expression of in vivo-produced equine embryos on different days of pregnancy (Day 8, N = 6; Day 10, N = 8; Day 12, N = 14) was analyzed. Insulin like growth factor-1 mRNA expression was evaluated by reverse transcription quantitative polymerase chain reaction. The sex of the embryo was determined by detection of X-inactivation specific transcript (Xist) RNA and equine sex determining region of the Y chromosome DNA. Embryos positive for Xist expression were classified as female, and Xist negative and equine sex determining region of the Y chromosome positive embryos were classified as male. From 28 embryos tested, 15 (54%) showed positive Xist expression and were thus classified as female. Insulin like growth factor-1 mRNA expression was influenced by sex (P = 0.01) but not by day of pregnancy (relative expression of IGF-1 in relation to β-actin, Day 8: male 5.1 ± 2.1, female 11.4; Day 10: male 5.2 ± 1.6, female 17.4 ± 6.7; Day 12: male 2.6 ± 0.3, female 11.6 ± 2.4). Results demonstrate an increased expression of IGF-1 in female equine embryos. Sex-related influences on expression of the IGF system are probably related to a gradual X chromosome inactivation.