Changes in urinary and plasma oestrone sulphate concentrations after induction of foetal death in mares at 45 days of gestation

Pregnancy monitoring in mares: Ultrasonographic and endocrine approaches

Methods to diagnose and monitor equine pregnancy continue to advance with improved instrumentation enabling the development of novel, non-invasive approaches to assess fetal well-being and viability using ultrasound and endocrine testing. From early embryonic loss to placentitis, that is typically encountered later in gestation, fetal viability and development as well as placental function can be evaluated using two fundamentally different, structural and functional, approaches. Ultrasound provides structural information on embryonic and fetal growth using such parameters as combined thickness of the uterus and placenta (CTUP), visual assessment of fetal fluids, activity, heart rate and multiple biometrics involving the fetal head and eyes, limbs and joints among many others, depending on the stage of gestation. Endocrine profiles that include progesterone and 5α-dihydroprogesterone, other metabolites, androgens and estrogens can be evaluated simultaneously using liquid chromatography-tandem mass spectrometry (LC-MS/MS) providing more functional information on fetal and placental competence and development. Endocrine information can be used in making clinical decisions including the need for progestin supplementation or when it can cease, and even estimating gestational stage in mares that cannot be easily palpated or scanned, as with mini-breeds or rancorous animals most notably. When used together, monitoring gestation by ultrasound and hormonal analysis provides unusual insight into feto-placental well-being and the progress of pregnancy, helping to identify problems needing therapeutic intervention.

Assessment of peripheral markers and ultrasonographic parameters in pregnant mares receiving intramuscular or intrauterine cloprostenol

The present study aimed to compare two methods of prostaglandin-induced abortion in mares by determining blood markers (progesterone, estradiol-17β, alpha-fetoprotein, 13,14-dihydro-15-keto-prostaglandin-F2α (PGFM)), B-mode ultrasonographic parameters, and time until loss of fetal heartbeat. It was hypothesized that intrauterine infusion of cloprostenol results in earlier fetal compromise than intramuscular administration. Ovarian structures (number and sizes of follicles and corpora lutea area), fetal heartbeat, and fetal mobility of thirteen singleton pregnancies were assessed daily by transrectal ultrasonography until induction of pregnancy termination (60 ± 2 days of gestation). Mares received 500 μg of cloprostenol intramuscularly every 12 h (IM, n = 7) or once transcervically (TC, n = 6). After initial cloprostenol administration, ultrasonographic examinations were repeated at 6-h intervals until loss of fetal heartbeat was detected. Plasma progesterone, estradiol-17β, and alpha-fetoprotein were assessed for five days before and after pregnancy loss. In addition, plasma PGFM concentrations were assessed immediately before cloprostenol administration (0 min), and then 15, 30, and 45 min, and 1, 2, 3, 4, 6, 12 h after administration. Data were analyzed using the MIXED procedure with repeated measures in SAS. Significance was set at P < 0.05. All mares lost their pregnancies within 48 h after initial cloprostenol administration, with no difference in time to pregnancy loss. There were significant effects of time starting by 12 h post-induction of pregnancy termination but there was no time by group interaction for progesterone concentrations. Estradiol-17β and alpha-fetoprotein concentrations were not altered upon impending abortion. Concentrations of PGFM increased significantly by 2 h after cloprostenol administration, but there were no differences between groups. No time effects or time by group interaction for fetal mobility and heartbeat was detected. Expectedly, the number and area of corpora lutea decreased significantly after cloprostenol administration with no significant differences between groups. In conclusion, intrauterine administration of cloprostenol was not different from repeated systemic administration to terminate the pregnancy. Both models for early fetal loss were equivalent for the endpoints assessed herein. The present study provides evidence that transcervical cloprostenol administration technique is repeatable in different settings and results in negligible side effects. While systemic administration results in colic-like signs and may result in severe reaction.

Concentrations of sulphated estrone, estradiol and dehydroepiandrosterone measured by mass spectrometry in pregnant mares

BACKGROUND

Few studies have provided a longitudinal analysis of systemic concentrations of conjugated oestrogens (and androgens) throughout pregnancy in mares, and those only using immunoassay. The use of liquid chromatography tandem mass spectrometry (LC-MS/MS) will provide more accurate concentrations of circulating conjugated steroids.

OBJECTIVES

To characterise circulating concentrations of individual conjugated steroids throughout equine gestation by using LC-MS/MS.

STUDY DESIGN

Longitudinal study and comparison of pregnant mares treated with vehicle or letrozole in late gestation.

METHODS

Sulphated oestrogens and androgens were measured in mares throughout gestation and mares in late gestation (8-11 months) treated with vehicle or letrozole to inhibit oestrogen synthesis in late gestation. An analytical method was developed using LC-MS/MS to evaluate sulphated estrone, estradiol, testosterone and dehydroepiandrosterone (DHEAS) during equine gestation.

RESULTS

Estrone sulphate concentrations peaked by week 26 at almost 60 μg/mL, 50-fold higher than have been reported in studies using immunoassays. An increase in DHEAS was detected from 7 to 9 weeks of gestation, but concentrations remained consistently low (if detected) for the remainder of gestation and testosterone sulphate was undetectable at any stage. Estradiol sulphate concentrations were highly correlated with estrone sulphate but were a fraction of their level. Concentrations of both oestrogen sulphates decreased from their peak to parturition. Letrozole inhibited estrone and estradiol sulphate concentrations at 9.25 and 10.5 months of gestation but, no increase in DHEAS was observed.

MAIN LIMITATIONS

Limited number of mares sampled and available for analysis, lack of analysis of 5α-reduced and B-ring unsaturated steroids due to lack of available standards.

CONCLUSIONS

Dependent on methods of extraction and chromatography, and the specificity of primary antisera, immunoassays may underestimate oestrogen conjugate concentrations in blood from pregnant mares and may detect androgen conjugates (neither testosterone sulphate nor DHEAS were detected here by LC-MS/MS) that probably peak coincident with oestrogen conjugates between 6 and 7 months of equine gestation.

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.

Absence of Effects From Immunocontraception on Seasonal Birth Patterns and Foal Survival Among Barrier Island Wild Horses

Despite a large body of safety data, concern exists that porcine zonae pellucidae (PZP) immunocontraception--used to manage wild horse populations--may cause out-of-season births with resulting foal mortality. Our study at Assateague, Maryland indicated the effects of immunocontraception on season of birth and foal survival between 1990 and 2002 on wild horses from Assateague Island. Among 91 mares never treated, 69 (75.8%) of foals were born in April, May, and June (in season). Among 77 treated mares, 50 (64.9%) were born in season. Of 29 mares foaling within 1 year after treatment (contraceptive failures), 20 (68.9%) were born in season. Of 48 mares treated for greater than 2 years then withdrawn from treatment, 30 (62.5%) of 48 foals were born in season. There were no significant differences (p <.05) between either treatment group or untreated mares. Survival did not differ significantly among foals born in or out of season or among foals born to treated or untreated mares. Data indicate a lack of effect of PZP contraception on season of birth or foal survival on barrier island habitats.

Rapid, convenient radioimmunoassay of estrone sulfate

We developed a specific, simple, and rapid RIA for the direct quantification of estrone sulfate (E1S) and established its performance characteristics. The assay has a dynamic range of 0.05–90 μg/L with a detection limit of 0.009 μg/L. Intraassay CVs were 9.2%, 4.5%, and 4.6% at 0.35, 9.0, and 60 μg/L, respectively. Interassay CVs were 8.8%, 5.1%, and 5.5% at 0.076, 0.5, and 12 μg/L, respectively. Linearity of dilution studies showed values of 80–105% of expected, and recovery of E1S added to serum samples ranged from 82% to 102%. Cross-reactivities with structurally related estrogens were &lt;5%. When compared with a conventional assay (involving hydrolysis of E1S and indirect measurement of estrone), the present RIA showed excellent correlation (r = 0.99, slope = 1.54, Sy‖x = 2.14, n = 71). Mean E1S concentrations measured with this RIA for normal men (n = 20) and women in follicular (n = 20) and luteal (n = 25) phases of their menstrual cycle were 0.96, 0.96, and 1.74 μg/L, respectively. Mean E1S concentrations for oral contraceptive users (n = 20) and postmenopausal women without hormone replacement therapy (n = 21) or on hormone replacement therapy (n = 22) were 0.74, 0.13, and 2.56 μg/L, respectively. Serum concentrations of E1S in pregnant women in their first (n = 14), second (n = 17), and third (n = 15) trimesters were 20, 66, and 105 μg/L, respectively. Availability of this simple RIA should provide a useful tool for the assessment of estrogen status in women.