Enzymeimmunoassay of oestrone sulphate concentrations in faeces for non-invasive pregnancy determination in mares

Pattern of faecal 20-oxopregnane and oestrogen concentrations during pregnancy in wild plains zebra mares

Regulative endocrine mechanisms influence the reproductive behaviour and success of mammals, but they have been studied predominantly in domestic and captive animals. The study aims at describing the pattern of faecal 20-oxopregnane and oestrogen concentrations during pregnancy in wild plains zebra Equus quagga chapmani. Data were collected during wet and dry seasons 2007-2009. Enzyme Immunoassays were used to determine 20-oxopregnane and oestrogen concentrations in faecal samples (n=74) collected from individual mares (n=32) whose dates of foaling were known through long-term monitoring. Hormonal profiles were described with a General Additive Model (GAM: Hormone ∼ Days to Foaling). Faecal 20-oxopregnanes have a complex cycle during pregnancy (GAM, n=70, R(2)=0.616, p<0.001). From -250 days to foaling, faecal 20-oxopregnane concentrations were above the baseline levels found in non-pregnant mares, peaking in the last 50 days. Faecal oestrogen levels showed a clear peak in mid-pregnancy (GAM, n=62, R(2)=0.539, p<0.001). The sex of the foetus and season had no detectable effect on hormone concentrations during pregnancy. High levels (>200 ng/g DW) of faecal 20-oxopregnanes associated with high (>160 ng/g DW) faecal oestrogen levels indicate mid-pregnancy in c.90% of cases (16/17). High faecal 20-oxopregnanes (>200 ng/g DW) and low faecal oestrogen levels (<160 ng/g DW) indicate late pregnancy, again in c.90% of cases. Two faecal samples would allow the stage of pregnancy to be determined with confidence.

The robustness of faecal steroid determination for pregnancy testing Kaimanawa feral mares under field conditions

AIMS

To investigate the utility of faecal oestrone sulphate (OS) concentrations for detecting pregnancy in mares during behavioural studies of feral horses, in which the collection and preservation of samples is not immediate.

METHODS

Oestrone sulphate concentrations were measured in fresh dung samples collected from 153 free-roaming Kaimanawa mares throughout the year. In addition, multiple samples were taken from the same pile to investigate the reliability of diagnosis from a single sample, as well as the influence of time until preservation on OS concentrations. Samples were also taken before and after a 10mm simulated rainfall event to test for dilution of OS concentrations by rain. Oestrone sulphate concentrations in all samples were measured using an enzyme immunoassay.

RESULTS

From approximately 150 to 250 days of gestation, OS concentrations were consistently >80 ng/g in mares which subsequently foaled. Mares which did not foal and had low faecal OS concentrations in multiple samples throughout the year had faecal OS concentrations of 31+/-13 ng/g (mean+/-s.d.) with an upper 95% confidence limit of 57 ng/g. Mares sampled from 1 week before to 1 month after behavioural oestrus, and that did not foal in the previous and subsequent seasons, had OS concentrations of 37+/-32 ng/g (mean+/-s.d.) with an upper 95% confidence limit of 100 ng/g. The standard error of oestrone sulphate concentrations in multiple samples from the same dung pile ranged from 1 to 37% of the mean. This large within-pile variation, however, did not result in incorrect diagnoses from single samples unless mares were within 18 days of parturition. Keeping samples at ambient temperatures for up to 16 hours did not affect OS concentrations. Simulated rainfall caused a 17% mean reduction in OS concentrations, but did not change pregnancy diagnoses.

CONCLUSIONS

Faecal OS concentrations >100 ng/g were indicative of pregnancy in Kaimanawa mares. For mares more than 150 days post-mating, OS concentrations <57 ng/g were indicative of non-pregnancy, while concentrations between 57 and 100 ng/g provided an inconclusive diagnosis. A single sample from each dung pile collected within 16 hours of defecation was sufficient to accurately diagnose pregnancy in mares 150-250 days post conception.

CLINICAL RELEVANCE

Measurement of OS concentrations in dung samples was a reliable and robust indicator of pregnancy status in feral mares 150-250 days post mating. This corresponds approximately to the period from May to August, given the seasonal breeding pattern in this population. This method of determining pregnancy status is suitable for field use in behavioural and demographic studies of wild horse populations.

Pregnancy status determination in mares using a rapid lateral flow test for measuring serum oestrone sulphate

AIMS

To develop a means of determining pregnancy status in horses based on measuring serum oestrone sulphate (OS) concentrations using a rapid lateral flow immunoassay, and to determine the assay's effectiveness using a visual end-point.

METHODS

Serum samples from mares >100 days post-mating (n=701) were assayed using a nitrocellulose membrane-based lateral flow immunoassay device. The device was developed using membrane-bound 1,3,5 (10)-estratrien-3-ol-17-one conjugated to bovine serum albumin as the capture antigen, and an OS-detection monoclonal antibody coupled to colloidal gold as the visible detection reagent. Concentrations of the coating antigen and OS monoclonal antibody were optimised so that the working range would allow pregnancy status to be determined from a visual end-point. The test was run by adding 0.1 ml serum to the sample well of a plastic cassette encasing the test membrane. As the serum migrated along the membrane, a test dot and control line were generated on it within 5-10 min. The intensity of the test dot was inversely proportional to the concentration of OS in the serum sample being tested. Results were compared with those from a validated OS enzyme immunoassay (EIA) and subsequent foaling or return to oestrus of the mares.

RESULTS

Serum samples with OS concentrations <10 ng/ml, indicative of non-pregnancy in mares >100 days post-mating, generated a test end-point consisting of a highly visible test dot and control line, whereas serum OS concentrations >50 ng/ml, indicative of pregnancy, generated a control line only. The test correctly identified 384/389 (98.7%) non-pregnant mares tested, and 303/312 (97.1%) pregnant mares tested that were >100 days post-mating. The lateral flow test devices were stable for at least 12 months when stored at 4 degrees C, sealed in aluminium pouches with desiccant.

CONCLUSION

This novel, rapid, easy-to-use, lateral flow immunoassay offers a practical alternative to traditional laboratory- based immunoassays for measuring serum OS concentrations in mares for determining their pregnancy status.

Factors influencing the measurement of oestrone sulphate by dipstick particle capture immunoassay

Factors influencing the performance of a dipstick competitive particle capture immunoassay (PCI) for the steroid oestrone sulphate (OS) were investigated. Appropriate 'blocking' of the nitrocellulose dipstick membrane was necessary for the upward flow of microsphere particles. Traditional protein blocking agents including BSA, gelatin and casein were unsatisfactory while synthetic polymers and surfactants were effective in promoting microsphere movement. A simple buffer consisting of 1% aqueous NaCl containing 0.05% Tween 20 was suitable for carrying the components up the dipstick and facilitating the antibody-antigen interactions. Increasing microsphere diameters from 0.3 to 0.8 microm allowed the microsphere antibody coating concentration to be reduced which enabled lower concentrations of OS to be measured. However, upward flow rate and the maximum signal attainable was compromised as a consequence. Enlarging the dipstick membrane nominal pore size from 3 to 12 microm increased the speed of test dot development, but assay sensitivity suffered as a result in some instances. Changing the capture antigen markedly influenced the dose-response lines. No dose-response was achieved with OG-BSA as the capture antigen while OHS-BSA and OCMO-BSA as capture antigens produced dose-response lines with means +/- S.E.M. EC(50) values of 140 +/- 16 and 19 +/- 1 ng/ml, respectively.