Luteal Tissue Area and Immunoreactive Concentration of Progesterone in Plasma of Bred and Non-bred Mares.
Authors: Colombo Ilaria, Podico Giorgia, Rudolf-Vegas Alba, Bauersachs Stefan, Canisso Igor F
Journal: Journal of equine veterinary science
Summary
# Editorial Summary This investigation examined whether progesterone concentration and corpus luteum size differ between pregnant and non-pregnant mares during the critical first 10 days post-ovulation, a period when supplementation decisions are typically made in clinical practice. Fifty-two oestrous cycles from 14 mares were monitored ultrasonographically; ovulation was induced with deslorelin, and mares were either bred artificially (37 cycles) or sham-bred as controls (15 cycles), with daily ultrasound assessment of luteal tissue area and daily blood sampling for progesterone quantification through 10 days post-ovulation. Surprisingly, progesterone concentrations and luteal tissue area evolved identically regardless of pregnancy status or breeding group (P > 0.05), though multiple ovulations—which occurred in some cycles—were strongly associated with elevated progesterone and larger luteal tissue area. The finding that seminal plasma did not influence luteal function challenges certain assumptions about breeding's systemic effects on corpus luteum development. Whilst these results suggest that early pregnancy itself does not trigger measurable changes in luteal steroidogenesis during this window, the cohort consisted of mares with apparently normal progesterone profiles (all exceeded 4 ng/mL by day 5); application to mares with documented luteal insufficiency remains unclear, and practitioners should continue using progesterone assays in mares with risk factors for early pregnancy loss rather than abandoning supplementation protocols based on these findings alone.
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Practical Takeaways
- •Routine progesterone supplementation based solely on concentration may not improve pregnancy rates in mares with normal luteal function, as pregnancy was not associated with elevated progesterone levels
- •Single versus multiple ovulations significantly impact progesterone production and luteal tissue development; mares with multiple ovulations show substantially higher concentrations, which may influence supplementation decisions
- •Since seminal plasma did not affect luteal function in this study, progesterone monitoring and support protocols should focus on other factors affecting early pregnancy loss rather than breeding-induced changes
Key Findings
- •Progesterone concentration and luteal tissue area varied with time but not between bred, non-bred, or pregnant mares (P > 0.05)
- •Multiple ovulations were associated with significantly greater progesterone concentration and luteal tissue area (P = 0.0001)
- •Moderate positive correlation existed between number of ovulations and luteal tissue area (r = 0.54; P = 0.0001)
- •All mares maintained progesterone >4 ng/mL after 5 days post-ovulation; pregnancy was not associated with higher progesterone concentrations