Reproductive Performance of Thoroughbred Mares in Sweden

During 1997–2001, a total of 430 Thoroughbred mares were mated by one of the two Thoroughbred stallions on a well‐managed stud farm in the central part of Sweden. On arrival, a thorough gynaecological examination of all mares was performed. An early pregnancy examination was performed on days 14 and 15 after ovulation. The overall conception rates for the two stallions were 92.2 and 88.8%, and the corresponding live foal rates were 82.6 and 75.2%, respectively. The mean number of served oestrous cycles was 1.60 per mare per conception and 1.86 per live foal. The first and second cycle conception rates are reported for different age groups, mare categories and month of mating. The age of the mares had a significant influence on the live foal rate, being lower for mares >13 years of age. Resorption and abortion occurred in higher percentages among mares >8 years of age. The highest embryonic death occurred among mares with a history of being barren, or with having resorbed or aborted foetuses during the previous season. The month of mating had no significant influence on the first cycle conception rate or the second cycle conception rate. The frequency of twinning was 10.5% and the results of manual crushing of one of the conceptuses was successful in 88.9% of all cases, according to the ultrasound scanning 2 days later.     

Hormone Profiles of Mares Affected by the Mare Reproductive Loss Syndrome

While searching for the cause of the Mare Reproductive Loss syndrome (MRLS), we postulated that 1 of 3 tissues in 40–120 D pregnant mares was the likely primary target of the noxious factor that caused early abortions: The corpora lutea (CL), the endometrium or the fetus and/or its membranes. At this stage of gestation, progesterone (P4) is solely produced by luteal tissue, eCG by endometrial cups in the endometrium and oestrogens by the feto‐placental unit. We determined whether concentrations of P4, eCG and/or total conjugated oestrogens (CE) would indicate which tissue was targeted during the MRLS. P4, eCG and CE were measured in single serum samples collected from 216 mares, 60–110 D after ovulation during the 2001 MRLS outbreak. All mares had previously been confirmed pregnant by ultrasonography. The following data was obtained from each mare: Interval from ovulation, pregnancy status and normalcy of fetal fluids at the time of sampling, and pregnancy status 3 weeks after sampling and at term. There were no meaningful differences in hormone concentrations between pregnant mares that had normal and excessively echogenic fetal fluids at the time of sampling. CE were lower (p < 0.05) in mares that aborted after sample collection than in mares the carried to term. In 8 mares from which multiple samples were obtained, CE consistently decreased prior to any decreases in P4 or eCG. Arguments are presented that lead to the hypothesis that the fetal trophoblast was the primary target of the MRLS agent.     

Relation Among Neutrophil Enzyme Activity,Lipid Peroxidation,and Acute-Phase Response in Foal Heat in Mares

Apart from functional abnormalities, genetic structural disorders and management problems endometritis is one of the major causes of infertility or subfertility in mares. However, the causes of postbreeding endometritis in foal heat have not been clearly resolved to date. The aim of this study was to search for the relationship between neutrophil activity, acute-phase proteins, and oxidative status to indicate the parameters, which can influence fertility in cold-blooded mares in foal heat. The blood for the experiment was collected from 16 cold-blooded mares at five time points: 6–8 days before parturition, 24 hours after parturition, at the first postpartum breeding on the ninth day, 24 hours after breeding, and 48 hours after ovulation. The obtained samples were assigned for hematological tests, assays of neutrophil activity, plasma malondialdehyde (MDA), and fibrinogen concentrations. We estimated that in susceptible mares during persistent postbreeding endometritis, neutrophil activity increased together with MDA and fibrinogen plasma level. Elastase release in resistant mares before parturition was 48.91 ± 1.75%, whereas in susceptible animals, the value reached 45.57 ± 1.9% of the maximal release. Myeloperoxidase release in resistant mares before parturition reached 13.95 ± 2.1%, then increased at three consecutive measurements, and returned to a value from before parturition at the last measurement. Myeloperoxidase level in susceptible mares was slightly lower than in resistant ones, then these values augmented at all measurements, reaching the maximum at the fourth one. The obtained results may help to indicate the predisposition to persistent postbreeding endometritis in cold-blooded mares bred at foal heat.     

Reproductive Parameters of Mangalarga Marchador Mares in a Commercial Embryo Transfer Programme

The objective of this study is to evaluate the reproductive efficiency in donors and recipient Mangalarga Marchador mares in commercial programmes of embryo transfer (ET) and the effects of some reproductive characteristics and ET methodology on conception rates in the recipient mares. A total of 1140 flushing procedures were performed and 830 embryos (72.8%) were recovered. There were no differences between the rates of embryonic recovery in the different breeding seasons (p > 0.05) and 92.8% of the recovered embryos were 8–9 days old. There was no difference in the embryonic recovery regarding the collection order from the first to the ninth embryo collection along the breeding season, as well as among mares inseminated during the foal heat or subsequent cycles (p > 0.05). Pregnancy rates observed in the total period of all reproductive seasons at 15, 30, 45 and 60 days of pregnancy were 73.4, 69.9, 66.7 and 64.5%, respectively. Differences in pregnancy rate and early embryonic loss rates were not observed between embryos transferred immediately after collection (66.8% and 13.5%) and embryos transported at room temperature for periods of <1 h (62.9% and 14.4%; p > 0.05). Pregnancy rates were higher when the interval between ovulations of donor and recipient mares remained between ?3 and ?2 days (p < 0.05), and the lowest rates were observed for intervals of ?6 days (p < 0.05) with intermediary values for intervals of ?1, 0 and +1 (p > 0.05). Embryonic loss rates, however, did not differ between intervals of ovulation’s synchronism between donor and recipient mares (p > 0.05). This flexibilization in the ovulatory synchronism between donor and recipient mares optimizes the use of recipient mares, thus reducing costs and facilitating management of horse breeding farms.     

Influence of Seroreactivity to Leptospira and Reproductive Failures in Recipient Mares of Equine Embryo Transfer Programmes

The aim of this study was to demonstrate that seroreactivity against Leptospira is significantly associated to the reproductive efficiency of recipient mares of an embryo transfer (ET) programme. A serosurvey was conducted from August 2007 to March 2009 in five herds from Rio de Janeiro, Brazil, with high rates of reproductive failure, as early embryonic death (>12%), abortion (>12%) and perinatal death. Detailed information about the losses was obtained from practitioner. A total of 338 recipient mares were tested by microscopic agglutination test, and 226 (66.9%) were seroreactive, mainly against serovars Bratislava and Copenhageni. Seroreactivity could be associated to reproductive failure (p < 0.001), and it was demonstrated that a seroreactive mare is 1.8 times more likely (relative risk – RR) to present reproductive failure than a seronegative one, particularly in relation to early embryonic death (p < 0.0001; RR 8.4) but also to abortions (p < 0.0001; RR 3.5), and to perinatal death (p < 0.05; RR 7.3). Therefore, seroreactivity to Leptospira is associated to reproductive failure in all phases of pregnancy in recipient mares, impairing equine ET programmes.     

Investigations on the Endometrial Response to Intrauterine Administration of N‐Acetylcysteine in Oestrous Mares

In mares, mating‐induced persistent endometritis contributes to low fertility. The condition is in part related to delayed clearance of mucus accumulated within the uterine lumen. The objective of this study was to investigate the endometrial response of healthy mares to intrauterine (i.u.) treatment with N‐acetylcysteine (NAC). Oestrous mares (n = 12) were randomly assigned to a treatment (TM) or control (C) group and received an i.u. infusion of 5% NAC and saline (total volume 140 ml), respectively. Endometrial biopsies were collected in five of the mares 24 h after treatment, in the remaining seven mares 72 h after treatment. Endometrial biopsies were evaluated for integrity of the luminal epithelium, number of polymorphonuclear neutrophils (PMN), staining for cyclooxygenase 2 (COX2), staining with Kiel 67 antigen (Ki‐67), lectins and periodic acid‐Schiff (PAS). The integrity of endometrial epithelial cells was not affected by treatment (no statistical differences between groups or times). At 24 h after treatment, the mean number of PMN in endometrial biopsies from NAC‐ and C‐mares did not differ, but at 72 h after treatment, number of PMN was significantly higher (p < 0.05) in C (3.9 ± 0.6 PMN/field) compared with NAC‐treated mares (2.3 ± 0.2 PMN/field). At 72 h after treatment, the intensity of staining for COX2 was significantly higher after saline than after NAC treatment (p < 0.05). In the epithelium, no differences in staining for the proliferation marker Ki‐67 were seen with respect to time and treatment. Score for the lectin wheat germ agglutinin (WGA) was slightly higher in NAC‐treated mares than in C‐mares 72 h after treatment (p < 0.05). Score for PAS staining of mucus in deep uterine glands differed significantly between groups at 24 h after treatment (p < 0.05). The present study demonstrates that NAC does not adversely affect the endometrial function. Moreover, an anti‐inflammatory effect on the equine endometrium was observed.     

Stress Response of Three-year-old Horse Mares to Changes in Husbandry System During Initial Equestrian Training

For initial training, horses are often transferred from group housing to individual boxes, which is a potential stressor. In this study, salivary cortisol concentrations, locomotion activity, and heart rate (HR) were analyzed and the HR variability (HRV) variables standard deviation of beat-to-beat interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated in 3-year-old mares (n = 8). Mares were transferred abruptly from a group stable with access to a paddock to individual boxes without a paddock and were studied from 4 days before to 5 days after changing the stable. Mares underwent routine equestrian training for young horses. On the days before mares were moved to individual boxes, cortisol concentrations showed a diurnal rhythm with values approximately 0.6 ng/ml in the morning and a decrease throughout the day. When horses were moved to individual boxes, cortisol concentrations increased to 1.8 ± 0.2 ng/ml within 30 minutes and did not return to baseline values within 6 hours (0.7 ± 0.1 ng/ml, P < .05 over time). On the following days, a diurnal rhythm was re-established but at a higher level than before the change of stable. Locomotion activity was higher when mares had access to a paddock than when kept in individual boxes. Heart rate increased for approximately 60 minutes when mares were separated from their group. In conclusion, separating young horses from their group and individual stabling are perceived as stressful.     

母马大、小卵泡的卵泡液代谢组学分析及其对卵泡发育的影响

本实验旨在研究母马大、小卵泡液代谢物的差异,从卵泡液代谢组层面初步探讨差异物对卵泡发育的影响及卵泡发育机制。选用8匹山东即墨地区母马的卵泡液进行代谢组学分析,大卵泡直径设为45～60 mm、小卵泡直径设为20～30 mm,采用超高液相色谱-高分辨质谱联用技术,通过主成分分析法(PCA)、偏最小二乘法-判别分析法(PLS-DA)得到大小卵泡液差异性物质质荷比。结果表明:在大卵泡液中含量多的代谢物有睾酮、1-棕榈酰溶血磷脂酸、β-硫酸雌醇、硫酸雌酮,小卵泡液中含量多的代谢物有硫酸吲哚酚、木子塘、水苏糖和3-脲基丙酸酯。综上可知,在大卵泡液中,上调物质主要是类固醇,比较单一集中,但小卵泡中不存在上调的类固醇物质,说明在母马中类固醇激素是促使卵泡发育的主要代谢物;在小卵泡液中,上调物质种类复杂,当优势卵泡出现时,可能有一些代谢物会抑制其余的小卵泡继续发育。     

Progestins in Mid- to Late-Pregnant Mares

Two experiments were conducted to determine when a placental source of progestin was sufficient for maintaining pregnancy in the mare. In the first study, embryos were transferred into ovariectomized mares and pregnancy was maintained with altrenogest^a Altrenogest treatment was terminated at either day 100 (n=6) or day 150 (n=6). Twelve ovarian-intact mares were assigned to a second experiment on day 100 of gestation. On day 160 of gesta- tion, these mares were assigned to one of three treatments: 1) ovariectomy on day 160 and given altrenogest to day 200 (n=4); 2) ovariectomy on day 180 and given altrenogest to day 250 (n=4); or 3) ovariectomy on day 200 and given altrenogest to day 300 (n=4). Blood samples were collected every 2 weeks from all mares in both experiments from day 100 to parturition and assayed for concentrations of pro- gestins. Pregnancy loss from day 100 to parturition was not different among groups in either experiment. Serum con- centrations ofprogestins in ovary-intact mares were greater (P<0.05) than those in ovariectomized pregnant mares until day 130, after which they were similar. Serum con- centrations of progestins in the ovariectomized pregnant mares rose gradually from day 100 until near parturition. Serum concentrations of progestins in the ovary-intact pregnant mares declined from day 100 to day 157, did not vary significantly from day 157 to day 245, then rose until near parturition. Serum concentrations ofprogestins tended to decrease the sixth day prior to parturition. From these     

Endometrial Phospholipase A2 Activity During the Oestrous Cycle and Early Pregnancy in Mares

The aim of this study was to determine phospholipase A2 (PLA2) kinetics and activity in the mare’s endometrium during the oestrous cycle and early pregnancy. Phospholipase A2 is responsible for the liberation of arachidonic acid from phospholipids, which is the first limiting step in prostaglandins synthesis. Phospholipase A2 activity was measured using an assay based on the liberation of oleic acid from 1‐palmitoyl‐2‐[¹⁴C] oleoyl phosphatidylcholine. The enzyme was shown to be calcium dependent, to have an optimum pH of 8 and an apparent Michaelis constant of 127 μm . Enzyme activity was low in the endometrium of early luteal phase tissue but increased significantly (p < 0.001) during the late luteal phase (5.39 ± 0.16; 3.48 ± 0.33, 6.85 ± 0.59, and 9.96 thinsp;± thinsp;1.23 thinsp;nmol oleic acid released/mg protein at oestrus, and Days 3, 8 and 14 after ovulation, respectively). The mean PLA2 activity in endometrial tissue from pregnant mares (4.23 ± 0.74) was significantly lower (p < 0.01) than from cyclic animals during late dioestrus (9.96 ± 1.23). The results indicate that PLA2 activity in equine endometrium changes with the stage of the oestrous cycle and thus may be influenced by systemic hormone concentrations. The inhibitory effects of conceptus products on secretion of prostaglandin during early pregnancy were associated with a competitive inhibitor that decreased endometrial PLA2 activity.     

Characterization of Glucose Response Curves after Insulin Injection in Sensitive versus Insensitive Mares

The glucose responses to intravenous injections of a range of doses of recombinant human insulin were determined for six mares known to be insulin sensitive and six mares known to be insulin insensitive, with the goal of better characterizing the regression lines resulting from the two categories of mares. Insulin doses between 8 and 198 mU of insulin per kg of body weight (mU/kg BW) were administered intravenously between September 13 and 26, 2010, starting with 50 mU/kg BW on the first day. Higher and lower doses were administered on alternate days to obtain percentages of decreases in blood glucose concentrations between 10% and 70%. Linear regression analysis revealed that insulin-insensitive mares have glucose response curves with higher y intercepts (P = .066), less steep slopes (P = .0003), and less goodness of fit (P = .053) in addition to the expected greater dose required to produce a 50% reduction in blood glucose concentrations (ED50; P = .006), despite the similarities between their body weights and those of insulin-sensitive mares. Linear and nonlinear regression of responses to the 32, 50, and 79 mU/kg BW insulin doses with the overall estimates of ED50 and the natural log of ED50 indicated that the 50 mU/kg BW dose had the greatest coefficient of determination (>0.95). Generally, it appears that estimates of insulin sensitivity based on a single injection of insulin or on multiple injections of insulin are least variable for insulin-sensitive mares.     

The Role of Equine Chorionic Gonadotropin in the Stimulation of Luteal Steroidogenesis in Mares Carrying Horse or Mule Pregnancies

The stimulatory role of equine Chorionic Gonadotropin (eCG) in the production of steroid hormones was evaluated during the first 4 months of pregnancy in mares impregnated by either stallions or jack donkeys. Twenty mares were divided in two groups: Mares in the first group were inseminated with stallion semen (horse pregnancies), and those in the second group were inseminated with donkey semen (mule pregnancies). Blood samples were collected twice weekly from day 30 to day 120 of pregnancy to determine the concentrations of eCG, progesterone, androstenedione, and testosterone. Analysis of variance for repeated measures was used to compare the concentrations of each hormone between groups. Linear regression models that considered the linear and quadratic effects of week of gestation as well as the linear and quadratic effects of the concentrations of eCG on the production of each steroid hormone were carried out. Concentrations of eCG, progesterone, and androstenedione were higher in horse than in mule pregnancies (P < .01 for eCG and P < .05 for progesterone and androstenedione). Testosterone concentrations were also higher in horse pregnancies than in mule pregnancies at weeks 7, 9, and 10 (P < .05). Regression analysis indicated that eCG had considerable stimulatory effects on the secretion of progesterone and androstenedione and weaker effects on the secretion of testosterone. The results suggest that eCG stimulates luteal production of progesterone, androstenedione, and testosterone in horse and mule pregnancies, these effects being more evident in horse pregnancies than in mule pregnancies due to the higher concentrations of eCG in horse pregnancies.     

端粒酶的活性及其调控机制

端粒酶由RNA模板、调节蛋白和催化亚等组成，对端粒细胞的稳定起着重要作用。本文介绍端粒酶的结构，端粒酶与体细胞，细胞衰老及肿瘤分子等之间的生物学意义，以及端粒酶的基因表达与转录，分子之间的相互作用等分子调控机制。     

Key Factors Affecting Reproductive Success of Thoroughbred Mares and Stallions on a Commercial Stud Farm

To evaluate factors contributing to fertility of thoroughbred mares, data from 3743 oestrous periods of 2385 mares were collected on a large thoroughbred farm in Ireland. Fourteen stallions (mean age 8.3 years; range 4–15 years) had bred 2385 mares (mean age 9.4 years; range 3–24 years). Maiden mares accounted for 12%, mares with a foal at foot for 64%, and barren, slipped or rested mares for 24% of the total. The mean pregnancy rate per cycle was 67.8% (68.6% in year 1 and 66.9% in year 2). Backward stepwise multivariable logistic regression analysis was utilized to develop two models to evaluate mare factors, including mare age, reproductive status, month of foaling, dystocia, month of cover, foal heat, cycle number, treatments, walk‐in status and stallion factors including stallion identity, stallion age, shuttle status, time elapsed between covers and high stallion usage on the per cycle pregnancy rate and pregnancy loss. Old age (p < 0.001) and cover within 20 days post‐partum (p < 0.003) were associated with lowered pregnancy rates. High mare age (p < 0.05) and barren, slipped or rested reproductive status (p = 0.05) increased the likelihood of pregnancy loss. Uterine inflammation or infection, if appropriately treated, did not affect fertility. Only high usage of stallions (used more than 21 times in previous week) was associated with lowered (p = 0.009) pregnancy rates. However, shuttle stallions were more likely to have increased (p = 0.035) pregnancy survival, perhaps reflecting a bias in stallion selection. In conclusion, mare age exerted the greatest influence on fertility; nonetheless, thoroughbreds can be effectively managed to achieve high reproductive performance in a commercial setting.     

Postpartum Ovarian Activity and Serum Estradiol-17beta Level in Thai Crossbred Native Mares

To study the postpartum ovarian activities for investigation of first postpartum oestrus, twenty-five Thai crossbred native mares were monitored after parturition by oestrous detection, transrectal palpation and reproductive ultrasonography. Blood samplings were also taken for estradiol-17beta (E2) analysis. The first ovulation occurred within 20 days postpartum in 92% (23/25) of the mares. The mean intervals of foaling to first oestrus and to first ovulation were 10.3 +/- 2.9 and 13.4 +/- 2.6 days (mean +/- SD) respectively. Serum E2 increased from 7.0 +/- 2.9 to a peak of 10.8 +/- 3.3 pg/ml (mean +/- SD) at 2 days before ovulation. In conclusion, from the study, it can be stated that the postpartum breeding management should be considered after day 10 postpartum by careful examination of ovarian activity with various methods. However, the uterine condition should be also estimated associated with the ovarian activity after parturition which may increase breeding performance and foal production.     

Use of Acupuncture to Induce Cyclicity in Anestrous Mares

Acupuncture is part of an Eastern system of medicine used for diagnosing, treating, and preventing disease. It has been used for the treatment of reproductive disorders in both human beings and domestic species. We hypothesized that acupuncture could be used to induce cyclicity in anestrous mares. In experiment 1, six anestrous mares were treated with acupuncture at Bai Hui, governing vessel (GV)-2, bladder (BL)-22, BL-23, BL-31, and BL-33 twice a week for 3 weeks, then once a week for an additional 8 weeks, whereas six anestrous mares served as controls. In experiment 2, six anestrous mares received acupuncture stimulation at Bai Hui, GV-1, BL-22, BL-23, and BL-28, with electroacupuncture (10 minutes at 50 Hz) at BL-22 and BL-28 bilaterally. In addition, vitamin B12 (3 mL, 1,000 mcg/mL) was injected in the vaginal fornix at the 3, 6, and 9 o’clock positions around the cervix. Six anestrous mares served as controls. Examinations and treatments were carried out twice a week until ovulation. In both experiments, ovarian activity was examined in all mares by transrectal ultrasonography and blood sample was obtained twice a week to determine progesterone concentrations. The time to first ovulation for experiment 1 was 14.0 ± 0.7 and 13.5 ± 1.0 weeks (mean ± SD) for the control and acupuncture groups, respectively (P = .60). In experiment 2, the time to ovulation was 9.0 ± 0.6 and 10 ± 0.3 weeks (mean ± SD) for the control and acupuncture groups, respectively (P = .19). No significant difference was found between the treated and control mares in either study.