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The cryotolerance of equine blastocysts larger than 300 µm can be improved by aspirating blastocoele fluid prior to vitrification; however, it is not known whether blastocoele aspiration also enables successful slow-freezing. The aim of this study was therefore to determine whether slow-freezing of expanded equine embryos following blastocoele collapse was more or less damaging than vitrification. Grade 1 blastocysts recovered on day 7 or 8 after ovulation were measured (>300-550 µm, n = 14 and > 550 µm, n = 19) and blastocoele fluid was aspirated prior to slow-freezing in 10% glycerol (n = 14), or vitrification (n = 13) in 16.5% ethylene glycol/16.5% DMSO/0.5 M sucrose. Immediately after thawing or warming, embryos were cultured for 24 h at 38 °C and then graded and measured to assess re-expansion. Control embryos (n = 6) were cultured for 24 h following aspiration of blastocoel fluid, without cryopreservation or exposure to cryoprotectants. Subsequently, embryos were stained to assess live/dead cell proportion (DAPI/TOPRO-3), cytoskeleton quality (Phalloidin) and capsule integrity (WGA). For 300-550 µm embryos, quality grade and re-expansion were impaired after slow-freezing but not affected by vitrification. Slow-freezing embryos >550 µm induced additional cell damage as indicated by a significant increase in dead cell proportion and disruption of the cytoskeleton; neither of these changes were observed in vitrified embryos. Capsule loss was not a significant consequence of either freezing method. In conclusion, slow-freezing of expanded equine blastocysts collapsed by blastocoel aspiration compromises post-thaw embryo quality more than vitrification.

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In vitro embryo production (IVEP) via Ovum Pick-Up (OPU) and Intracytoplasmic Sperm Injection (ICSI) has become a popular breeding technique in Warmblood mares because of the high success rate and several practical advantages. IVEP offers a solution for a variety of reproductive issues including, but not limited to, sub-fertility in stallions or mares, poor quality or scarce frozen semen, difficulty in synchronizing donor and recipient mares, and inefficient use of recipient mares. In 515 OPU-ICSI sessions performed in our facility in 2021, a mean of 25.9 antral follicles were aspirated yielding an average 13.8 immature oocytes, which were shipped overnight to a specialized ICSI laboratory (Avantea). One or more blastocysts (range: 0-13 blastocysts) were produced from 78% of procedures with a mean of 2.12 blastocysts per session; the likelihood of pregnancy after transfer of a cryopreserved thawed IVP blastocysts in 2021 (n = 781) was 77.7%. Several donor mare, recipient mare, stallion and embryonic factors influence the likelihood of producing an in vitro blastocyst or achieving pregnancy. Approximately 60% of the transferred IVP blastocysts yield a foal; moreover, neither gestation length nor the health of foals is noticeably influenced by IVEP. On the other hand, a skewed sex ratio towards colts is apparent among IVEP foals resulting from day 7 but not day 8 embryos, suggesting that male embryos develop more rapidly in vitro. Although serious complications after OPU are uncommon, owners should be aware of their existence, because some complications can be life-threating.

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BACKGROUND: Monozygotic multiple pregnancy is rare in horses, but may be more common after transfer of an in vitro produced (IVP) embryo. OBJECTIVES: To determine the occurrence, incidence, characteristics and outcome of monozygotic siblings arising from in vivo and IVP equine embryos. STUDY DESIGN: Retrospective case series. METHODS: A total of 496 fresh in vivo and 410 frozen-thawed IVP blastocysts, produced by intracytoplasmic sperm injection (ICSI) of in vitro matured oocytes from Warmblood mares, were transferred into recipient mares. The likelihoods of pregnancy and multiple pregnancy were calculated, and the clinical features and outcome of any multiple pregnancy were recorded. RESULTS: The likelihood of pregnancy after transfer of a single IVP or in vivo embryo was 62% (254/410) and 83% (413/496) respectively. The incidence of multiple pregnancy was 1.6% (4/254) and 0% (0/413) for IVP and in vivo blastocysts, respectively. More specifically, three IVP blastocysts yielded twin embryo propers/fetuses, and one IVP conceptus developed three distinct embryonic bodies. Interestingly, only one embryonic vesicle was detected at all ultrasonographic examinations prior to embryo proper development. Multiple embryonic bodies only became apparent at later scans to check for an embryo proper and heartbeat, or when the recipient mare aborted. Two twin pregnancies aborted spontaneously at 3 and 9 months, respectively, while the heartbeat was lost from all three embryos in the triplet pregnancy before day 35 of gestation. Twin reduction by per rectum compression of one fetal thorax was attempted at day 50 of gestation in the fourth case; however, both fetuses were lost. MAIN LIMITATIONS: Small number of cases. CONCLUSIONS: In vitro embryo production resulted in a higher incidence of multiple monozygotic pregnancy, which could only be diagnosed after development of the embryo proper and is likely to result in pregnancy loss later in gestation if left untreated.

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Equine embryos tolerate an unusually large degree of negative uterine asynchrony (recipient mare up to 5 days behind the donor mare). By contrast, positive asynchrony of more than 2 days results in a high incidence of early embryonic loss (EEL). Day 8 embryos range in diameter from approximately 130-1300 µm, with embryos smaller than 300 µm reported to suffer an increased incidence of EEL. However, it is not known whether this reduced viability is due to intrinsically poor embryo quality, or to inadvertent recipient uterine stage-embryo (positive) asynchrony. To examine whether small embryos survive better in Day 4-5 recipients than in recipients with a more advanced uterine stage, the likelihood of pregnancy (PR) and EEL for 62 small (<300 µm) and 215 larger Day 8 horse embryos were compared after transfer to recipients at different uterine stages (Days 4-5, 6-7 and 8-9) using logistic regression. Overall, EEL was higher (21.2%; P < 0.05) for small than larger embryos (7.1%). However, neither PR nor EEL were influenced by the recipient's uterine stage at the time of transfer (P > 0.1). The EEL for small embryos transferred into Day 4-5, 6-7 and 8-9 recipients was 20.8, 18.7 and 25.0%, respectively. We conclude that embryos recovered on Day 8 with a diameter <300 µm are at increased risk of EEL due to reasons other than inadvertent positive asynchrony with the recipient mare's uterus.

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BACKGROUND: Advanced mare age is associated with declining fertility and an increased risk of early pregnancy loss. Compromised oocyte quality is probably the primary reason for reduced fertility, but the defects predisposing to embryonic death are unknown. In women, advanced age predisposes to chromosome segregation errors during meiosis, which lead to embryonic aneuploidy and a heightened risk of miscarriage. OBJECTIVES: To evaluate the effect of advanced mare age on chromosome alignment and meiotic spindle morphology in in vitro-matured (IVM) oocytes. STUDY DESIGN: Morphometric and morphological analysis. METHODS: To investigate differences in spindle organisation and chromosome alignment between young and old mares, oocytes collected from slaughtered mares were divided into two groups depending on mare age (young, ≤14 years and old, ≥16 years), IVM and stained to visualise chromatin and alpha-tubulin. Spindle morphology, morphometry and chromosome (mis)alignment were evaluated by confocal microscopy and 3D image analysis. RESULTS: Oocytes from old mares showed a higher incidence of chromosome misalignment (47.4% vs. 4.5%; P<0.001) and a thicker metaphase plate (mean ± s.d.: 5.8 ± 1.0 µm vs. 4.9 ± 0.9 µm; P = 0.04) than oocytes from young mares. Although no differences in spindle morphometry were detected between old and young mares, an increased major spindle axis length was associated with chromosome misalignment (mean ± s.d.: 25.3 ± 6.1 µm vs. 20.8 ± 3.3 µm; P = 0.01) irrespective of age. MAIN LIMITATIONS: The oocytes were IVM and may not exactly reflect chromosome misalignment in vivo. CONCLUSIONS: Advanced mare age predisposes to chromosome misalignment on the metaphase II spindle of IVM oocytes. The compromised ability to correctly align chromosomes presumably predisposes to aneuploidy in resulting embryos and thereby contributes to the age-related decline in fertility and increased incidence of early pregnancy loss. The Summary is available in Portuguese - see Supporting Information.

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The diameter of embryos recovered from mares on Day 8 after ovulation varies greatly, from as little as 130 µm to as much as 2500 µm. Several factors have been proposed to affect embryo size at recovery, one of which is the type of semen (frozen vs fresh or cooled-transported) used to inseminate the mare. In addition, it has been shown that smaller embryos (<300 µm) recovered on Day 8 are less likely than larger embryos to result in successful pregnancy after transfer. However, whether the actual age of the embryo (interval from fertilization to flushing) in relation to its size also influences the post-transfer viability is unclear. The aims of this study were: a) To determine the effect of semen type (frozen-thawed vs cooled-transported) on embryo diameter after pre-ovulatory insemination; and b) To establish the relationship between embryonic age, embryo size and likelihood of pregnancy and pregnancy loss following transfer. A total of 179 embryos were recovered from mares inseminated with: frozen semen post-ovulation 8 days previously (G1; n = 35); cooled-transported semen pre-ovulation 8.5 days previously (G2; n = 95); frozen semen pre-ovulation 8.5 days previously (G3; n = 30); and frozen semen post-ovulation 9 days previously (G4; n = 19). The effect of embryonic age, type of semen, donor mare and its age, number of ovulations and embryos per flush on embryo diameter was tested using a general linear model of variance. In addition, the proportions and survivals of small embryos (<300 µm) in each group were compared with those of respective larger embryos by Fisher's exact test. Embryonic age (P < 0.001) and age of the donor mare (P = 0.07), but no other factor, influenced embryo diameter. The proportion of small embryos was 42.9, 10.5, 10.0 and 10.5% for Groups 1, 2, 3 and 4, respectively. The pregnancy status of recipient mares 35 days post-transfer for small embryos from Group 1 (12/15; 80.0%) was not different (P > 0.1) from that of recipients of small embryos from Groups 2 to 4 combined (8/15; 53.3%).

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Health risks associated with obesity are more likely a factor of the localization of fat excess, rather than of elevated BW per se. The aim of this randomized controlled clinical trial was to determine the effect of a long-term high energy diet on BW, fat accumulation and localization. Eight Shetland pony mares, 3 to 7 years old, were randomly divided into a control and a high energy (HE) diet group fed either maintenance or double maintenance energy requirements (200% net energy (NE)) for two consecutive summers, with a low energy diet in the winter in between. Body condition score (BCS) did not differ between the groups at the onset of the study (control 5.6±0.75 v. HE 6.3±0.5). From 12 weeks after starting the diet, ultrasonography of five different locations (retroperitoneal, axillary, withers, intercostal and rump) for adipose deposition, BCS and BW were measured monthly during the period that ponies received different diets. Statistical analysis was performed using a linear mixed-effects model with post hoc Bonferroni testing. P values <0.05 were considered significant. At week 12 after the onset of the diet, fat thickness in the HE group was significantly greater than in the control group. During the monitoring period, the HE group showed a significant increase in mean (±SE) BW (+52%, 265±13.94kg) and BCS (+70%; to 9.0±0.4), while the control group was unchanged (BW 160±13.98 kg; BCS 3.8±0.4). At all locations, the fat depth in the HE group increased significantly, with the highest increase noted for retroperitoneal deposits. The conclusions were that a 200% NE diet induced subcutaneous and retroperitoneal fat accumulation, with the greatest increase in intra-abdominal deposits. The moderate increase of the subcutaneous fat depth followed by a plateau phase suggests the existence of a limit of adipose tissue expandability, as in man.

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To investigate the hypothesis that oxidative phosphorylation is a major source of ATP to fuel stallion sperm motility, oxidative phosphorylation was suppressed using the mitochondrial uncouplers CCCP and 2,4,-dinitrophenol (DNP) and by inhibiting mitochondrial respiration at complex IV using sodium cyanide or at the level of ATP synthase using oligomycin-A. As mitochondrial dysfunction may also lead to oxidative stress, production of reactive oxygen species was monitored simultaneously. All inhibitors reduced ATP content, but oligomycin-A did so most profoundly. Oligomycin-A and CCCP also significantly reduced mitochondrial membrane potential. Sperm motility almost completely ceased after the inhibition of mitochondrial respiration and both percentage of motile sperm and sperm velocity were reduced in the presence of mitochondrial uncouplers. Inhibition of ATP synthesis resulted in the loss of sperm membrane integrity and increased the production of reactive oxygen species by degenerating sperm. Inhibition of glycolysis by deoxyglucose led to reduced sperm velocities and reduced ATP content, but not to loss of membrane integrity. These results suggest that, in contrast to many other mammalian species, stallion spermatozoa rely primarily on oxidative phosphorylation to generate the energy required for instance to maintain a functional Na+/K+ gradient, which is dependent on an Na+-K+ antiporter ATPase, which relates directly to the noted membrane integrity loss. Under aerobic conditions, however, glycolysis also provides the energy required for sperm motility.

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Colour-flow Doppler sonography has been described as a means of assessing corpus luteum (CL) function rapidly, because area of luteal blood vessels correlates well with circulating progesterone (P4) concentrations [P4] in oestrous cycling mares. The aim of this study was to assess the relationships between CL size and vascularity, and circulating [P4] during early pregnancy in mares, and to determine whether luteal blood flow was a useful aid for selecting an embryo transfer recipient. Equine embryos (n=48) were recovered 8 days after ovulation and were transferred to available recipient mares as part of a commercial program with the degree of synchrony in timing of recipient ovulation ranging from 1 day before to 4 days after the donor. Immediately prior to embryo transfer (ET), maximum CL cross-section and blood vessel areas were assessed sonographically, and jugular blood was collected to measure plasma [P4]. Sonographic measurements and jugular blood collection were repeated at day 4 after ET for all mares, and again at days 11, 18 and 25 after ET in mares that were pregnant. The number of grey-scale and colour pixels within the CL was subsequently quantified using ImageJ software. The CL blood flow correlated significantly but weakly with plasma [P4] on the day of transfer and on day 4 after ET in all mares, and on days 11 and 25 after ET in pregnant mares (r=0.30-0.36). The CL area and plasma [P4] were also correlated on each day until day 11 after ET (r=0.49-0.60). The CL colour pixel area decreased significantly after day 18, whereas CL area was already decreasing by day 4 after ET. The CL area, area of blood flow, or [P4] was predictive of pregnancy. Findings in the present study suggest that both CL area and blood flow are correlated with circulating [P4] at the time of transfer and in early pregnancy. Evaluation of the CL using B-mode or CF sonography, although practical, provides no improvement in the selection of recipients or prediction of pregnancy outcomes than methods employed currently.

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REASONS FOR PERFORMING STUDY: Previous surveys have reported that mare and foal survival after correction of uterine torsion (UT) varies from 60 to 84% and from 30 to 54%, respectively. Furthermore, resolution via a standing flank laparotomy (SFL) has been associated with better foal, but not mare, survival. OBJECTIVES: To compare the success of SFL with other correction methods (e.g. midline or flank laparotomy under general anaesthesia; correction per vaginam). STUDY DESIGN: Retrospective analysis of clinical records. METHODS: Data on correction technique, stage of gestation, degree of rotation, survival and subsequent fertility for 189 mares treated for UT at 3 equine referral hospitals in The Netherlands during 1987-2007 were analysed. RESULTS: Mean stage of gestation at diagnosis was 283 days (range 153-369 days), with the majority of UTs (77.5%) occurring before Day 320 of gestation. After correction of UT, 90.5% of mares and 82.3% of foals survived to hospital discharge, between 3 and 39 days later, and to foaling. Multivariable logistic regression indicated that correction method and stage of gestation at UT affected survival of foals and mares. For foals, survival was 88.7% after SFL compared with 35.0% after other methods (P = 0.001). When UT occurred at <320 days, 90.6% of foals survived, compared with 56.1% at ≥320 days (P = 0.007). For mare survival, an interaction between stage of gestation and correction method was detected (P = 0.02), with higher survival after SFL (97.1%) than other methods (50.0%) at <320 days of gestation (P<0.01). When UT occurred at ≥320 days, mare survival did not differ between techniques (76.0 vs. 68.8%; P = 0.6). Of 123 mares that were bred again, 93.5% became pregnant; fertility did not differ between mares treated by SFL (93.9%) and other techniques (87.5%; P = 0.9). CONCLUSIONS: Standing flank laparotomy is the surgical technique of choice for resolving uncomplicated equine UT (i.e. with no coexisting gastrointestinal lesions) except when the stage of gestation exceeds 320 days.

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Short-term storage of equine sperm at 5°C in an extender containing milk and/or egg yolk components is common practice in the equine breeding industry. Sperm motility, viability, DNA integrity and, consequently, fertilizing ability decline over time, partly due to reactive oxygen species (ROS) generation. We investigated whether adding the anti-oxidant d-penicillamine to a commercial milk/egg yolk extender delayed the decrease in semen quality. Semen was recovered on four consecutive days from eight 3-year old Warmblood stallions. On day 5, seven of the stallions were castrated and sperm recovered from the caudae epididymides. Ejaculated samples were split, and one portion was centrifuged and re-suspended to reduce seminal plasma content. All samples were diluted to 50millionsperm/ml and divided into two portions, one of which was supplemented with 0.5mM d-penicillamine. After 48h, 96h, 144h and 192h storage, sperm motility was assessed by computer-assisted semen analysis (CASA), viability by SYBR14/PI staining, and DNA integrity using the sperm chromatin structure assay (SCSA). d-Penicillamine had no effect on motility of ejaculated sperm (P>0.05) but reduced total and progressive motility of epididymal sperm. Sperm chromatin integrity was not influenced by storage time, seminal plasma or d-penicillamine. In short, adding d-penicillamine to a commercial semen extender was neither beneficial nor detrimental to the maintenance of quality in ejaculated semen stored at 5°C. The negative effect on motility of epididymal sperm may reflect differences in (membrane) physiology of spermatozoa that have not been exposed to seminal plasma.

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Leukaemia inhibitory factor (LIF) plays a critical role in blastocyst development and implantation in several species. The present study investigated mRNA and protein expression for LIF, as well as the low-affinity LIF receptor (LIFR) and interleukin-6 signal transducer (IL6ST), in equine endometrium, trophoblast and histotroph during early pregnancy and in the endometrium during the oestrous cycle. Endometrial LIF mRNA expression was upregulated after Day 21 of pregnancy, whereas LIF immunoreactivity increased in the endometrium on Day 28. Expression of LIF mRNA in the yolk sac membrane increased from Day 21 of pregnancy, whereas LIF immunoreactivity increased from Day 28 in the trophoblast. LIFR and IL6ST mRNA was expressed in the endometrium during both the oestrous cycle and early pregnancy and, although LIFR and IL6ST protein were localised to the glandular epithelium during the cycle and first 14 days of pregnancy, from Day 21 they were located in the luminal epithelium. Trophoblast expression of LIFR and IL6ST increased as pregnancy proceeded. In conclusion, LIF expression increased at the conceptus-maternal interface during capsule attenuation. Because contemporaneous upregulation of both LIFR and IL6ST was also observed in the trophoblast, we propose that LIF plays an important role in the development of endometrial receptivity for trophoblast growth, apposition and adhesion in mares.

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The aim of this study was to determine whether flow cytometric evaluation of combined merocyanine 540 and Yo-Pro 1 (M540-YP) staining would identify viable dog sperm that had undergone membrane stabilization known to be associated with capacitation in other species, and whether such destabilization is detected earlier than when using the tyrosine phosphorylation and ethidium homodimer (TP-EH) stain combination with epifluorescence microscopy. Semen from nine dogs was collected and incubated in parallel in bicarbonate-free modified Tyrode's medium (-BIC), medium containing 15 mM bicarbonate (+BIC), dog prostatic fluid, and in PBS. Aliquots for staining were removed at various time points during incubation of up to 6 hours. Staining with M540-YP allowed the classification of dog sperm as viable without destabilized membranes, viable with destabilized membranes, nonviable without destabilized membranes, or nonviable with destabilized membranes. The percentage of viable sperm detected using EH (83.5 ± 1.37%; mean ± SEM) was higher than when using YP (66.7 ± 1.37%: P < 0.05; n = 54 semen samples). On the other hand, M540-YP identified a higher percentage of viable sperm with destabilized membranes than TP-EH (75 ± 1.76% vs. 35 ± 1.70%: P < 0.05; n = 54 semen samples). Staining with M540-YP indicated a rapid increase in the percentage of viable sperm with destabilized membranes, reaching a maximum during the first 30 minutes of incubation in +BIC. For all other treatments (i.e., -BIC, prostatic fluid, and PBS), the peak in the percentage of viable sperm with destabilized membranes was reached as much as 90 to 210 minutes later than incubation in +BIC. The lowest percentage of viable sperm showing signs of capacitation was recorded during incubation in PBS. We conclude that YP identifies sperm committed to cell death earlier than EH, and that the M540-YP stain combination identifies membrane destabilization known to be associated with capacitation in other species earlier than the TP-EH stain combination.

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REASONS FOR PERFORMING STUDY: Equine herpesvirus 1 (EHV-1) is one of the most common causes of infectious abortion in mares. Analysing the demography of outbreaks and detailing subsequent reproductive performance of affected mares will assist in the management of future (threatened) epizootics. OBJECTIVES: To examine the epidemiology and reproductive outcomes of 2 EHV-1 abortion epizootics with very different patterns of morbidity. STUDY DESIGN: Epidemiological and reproductive data were analysed retrospectively following abortion epizootics associated with EHV-1, but initiated via different routes, among unvaccinated mares on 2 Thoroughbred farms in South Africa. METHODS: Aborting mares were assigned to either the EHV-1 abortion cohort via positive immunostaining (Farms 1 and 2) or quantitative PCR (Farm 2) on tissue samples, or to the non-EHV abortion cohort. RESULTS: During their respective epizootics, EHV-1 abortions affected 9/30 (30.0%) and 18/316 (5.7%) of the pregnant mares on Farms 1 and 2, respectively; there were also 25 (7.9%) non-EHV abortions on Farm 2. Epizootic differences included: durations (Farm 1 = 135 days; Farm 2 = 34 days), intervals between first and subsequent abortions (Farm 1 = 39 days; Farm 2 = 2 days) and intervals to confirmation of EHV-1 (Farm 1 = 40 days; Farm 2 = 2 days). The median (range) age of EHV-1 abortion mares (8.0; 5-18 years) in both epizootics was similar but significantly younger (P = 0.004) than the 25 non-EHV-1 abortion mares (11.0; 4-24 years) on Farm 2. Gestation stage (median; range) of EHV-1 (291.5; 277-313) and non-EHV-1 (211.9; 61-339 days) abortions were significantly different (P = 0.001). The post abortion complications and subsequent reproductive outcomes had no significant association with EHV-1 abortion. CONCLUSIONS: The marked difference in morbidity between the 2 epizootics may be associated with routes of introduction or intervention strategy dictated by availability of molecular diagnostic techniques. Unexpectedly, EHV-1 was not more commonly associated with post abortion complications.

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REASONS FOR PERFORMING STUDY: Equine embryos are cryopreserved by slow-freezing or vitrification. While small embryos (<300 µm) survive cryopreservation reasonably well, larger embryos do not. It is not clear if slow-freezing or vitrification is less damaging to horse embryos. OBJECTIVES: To compare the type and extent of cellular damage suffered by small and large embryos during cryopreservation by slow-freezing vs. vitrification. STUDY DESIGN: Sixty-three Day 6.5-7 embryos were subdivided by size and assigned to one of 5 treatments: control, exposure to slow-freezing or vitrification cryoprotectants (CPs), and cryopreservation by either technique. METHODS: After thawing/CP removal, embryos were stained with fluorescent stains for various parameters of cellular integrity, and assessed by multiphoton microscopy. RESULTS: Exposing large embryos to vitrification CPs resulted in more dead cells (6.8 ± 1.3%: 95% confidence interval [CI], 3.1-10.4%) than exposure to slow-freezing media (0.3 ± 0.1%; 95% CI 0.0-0.6%: P = 0.001). Cryopreservation by either technique induced cell death and cytoskeleton disruption. Vitrification of small embryos resulted in a higher proportion of cells with fragmented or condensed (apoptotic) nuclei (P = 0.002) than slow-freezing (6.7 ± 1.5%, 95% CI 3.0-10.4% vs. 5.0 ± 2.1%, 95% CI 4.0-14.0%). Slow-freezing resulted in a higher incidence of disintegrated embryos (P = 0.01) than vitrification. Mitochondrial activity was low in control embryos, and was not differentially affected by cryopreservation technique, whereas vitrification changed mitochondrial distribution from a homogenous crystalline pattern in control embryos to a heterogeneous granulated distribution in vitrified embryos (P = 0.05). CONCLUSIONS: Cryopreservation caused more cellular damage to large embryos than smaller ones. While vitrification is more practical, it is not advisable for large embryos due to a higher incidence of dead cells. The choice is less obvious for small embryos, as vitrification led to occasionally very high percentages of dead or damaged cells, but a lower incidence of embryo disintegration. Modifications that reduce the level of cellular damage induced by vitrification are required before it can be considered the method of choice for cryopreserving equine embryos.

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Endometrial oxytocin receptors (OXTR) and prostaglandin-endoperoxide synthase 2 (PTGS2) are central components of the luteolytic pathway in cyclic mares, and their suppression is thought to be critical to luteal maintenance during early pregnancy. We examined the effect of pregnancy on endometrial expression of potential regulators of prostaglandin (PG) F2α secretion in mares. Expression of the nuclear progesterone receptor and oestrogen receptor ERα was high during oestrus, and depressed when progesterone was elevated; the opposite applied to the membrane progesterone receptor. PTGS2 was upregulated on Day 14 of dioestrus, but not pregnancy. Although OXTR mRNA expression was not elevated on Day 14 of dioestrus, protein abundance was; this increase in OXTR protein was absent on Day 14 of pregnancy. Intriguingly, gene and protein expression for PTGS2 and OXTR increased markedly between Days 14 and 21 of pregnancy suggesting that, although initial avoidance of luteolysis during pregnancy involves their suppression, this is a transient measure that delays rather than abolishes luteolytic pathway generation. The only oxytocin-PGF2α feedback loop component downregulated on both Days 14 and 21 of pregnancy was the PGF2α receptor we propose that downregulation of the PGF2α receptor uncouples the oxytocin-PGF2α feedback loop, thereby preventing generation of the large PGF2α pulses required for luteolysis.

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In captivity, male Asian elephants often yield poor quality semen after transrectal manually assisted semen collection; however, the reasons for the disappointing semen quality are not clear. Here we test the hypothesis that accumulation of senescent spermatozoa is a contributory factor, and that semen quality can therefore be improved by more frequent ejaculation. To this end we investigated the effect of collecting semen five times on alternate days, after a long period of sexual rest, on semen quality in Asian elephants known to deliver poor semen during infrequent single collections. All eight bulls initially displayed a high incidence of detached sperm heads and low percentages of motile (close to 0%) spermatozoa. After semen collection on alternate days, the percentages of detached sperm heads, and head and mid-piece abnormalities, were reduced significantly (p<0.05). In particular, one bull showed markedly improved sperm motility (increased from 0% to 60%) and membrane integrity (increased from 5% to 75%). In addition, advancing age significantly (p<0.01) correlated with lower percentages of sperm with intact membranes and a higher frequency of detached sperm heads. In contrast to sperm accumulation problems in other species, a small ampullary diameter correlated significantly (p<0.05) with reduced semen quality.

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