Changes in oestrone sulphate concentrations in peripheral plasma of Pony mares associated with follicular growth, ovulation and early pregnancy.

The research develops a quick immunoassay method, named LIDIA, for measuring oestrone sulphate concentration in the blood plasma of Pony mares. Through it, the researchers track hormone changes in the mares during follicle growth, ovulation, and early pregnancy.

Method Development

• The researchers developed an immunoassay method that’s quick (under 2 hours) and straightforward, capable of estimating the concentration of a specific hormone, oestrone sulphate, in the ethanolic extracts of blood plasma. This technique is called LIDIA, short for Ligand Differentiation Immunoassay.
• Central to this method is the use of antiserum developed against oestrone-3-glucuronyl-BSA. The antiserum exhibited a stronger cross-reaction with the sulphate metabolite compared to the glucuronide counterpart, hence its use.
• The sensitivity of this assay method is documented to be 5.2 picograms per tube, with intra-assay precision less than 8.5% and inter-assay precision less than 18%, making it precise enough for their study.

Follicular Growth and Ovulation

• The method was used to analyze daily samples of peripheral venous plasma obtained from Pony mares. Changes were observed starting from 6 days prior to follicular rupture. The concentration of oestrone sulphate rose from a baseline value of less than 300 picograms per milliliter (pg/ml).
• Two days before the rupture of a follicle (as determined by rectal palpation), the concentration of oestrone sulphate peaking at over 850 pg/ml.
• Progesterone concentrations, on the other hand, only started to rise from baseline (less than 0.5 nanograms per milliliter or ng/ml) on the day of ovulation and peaked eight days later.

Early Pregnancy

• During the first 30 days of pregnancy, the team also took regular samples for analysis.
• They found that there was no increase in the levels of oestrone sulphate at the time oestrus would have been expected, that is, had the mares not conceived.

To sum up, the LIDIA method functions as a reliable and efficient method for gauging oestrone sulphate concentrations. Through it, the researchers tracked follicular growth, ovulation, and early signs of pregnancy in Pony mares.