The correlation of endogenous progesterone concentration in diestrus on early pregnancy rate in Thoroughbred mares.

Fiona Hollinshead, M.K. Mehegan, Allan Gunn, T. Nett, J.E. Bruemmer, David Hanlon

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Aim: The aim of this project was to test the hypothesis that progesterone concentration 5 days after ovulation did not differ between pregnant and nonpregnant Thoroughbred mares on stud farms located in the Waikato region of New Zealand. Methods: A prospective cohort study was performed involving five stud farms in the Waikato region of New Zealand during the 2018 breeding season. A total of 275 mares were enrolled in the study. Mares were served by 34 individual stallions. Blood samples were taken from each mare 5 days after ovulation (D0) and measured for progesterone concentration. Early pregnancy
was confirmed at D14 by transrectal palpation and ultrasonography of the mares reproductive tract.
Results: Progesterone concentration at Day 5 post-ovulation was higher in mares determined to pregnant at Day 14 of gestation than in mares determined to be non-pregnant at Day 14 (6.4 ± 3.0 ng/ml vs 5.5 ± 3.3 ng/ml respectively; P=0.02). A negative association between increasing mare age and pregnancy rate was found but mare age had no effect on progesterone concentration at D5.
Conclusions: In this study we found that although higher serum progesterone concentration at Day 5 post ovulation was associated with a higher pregnancy rate at Day 14, no predictive or definitive minimum required progesterone concentration could be identified. Additional studies are required to determine if a synthetic progestogens can serve to supplant natural progesterone to increase pregnancy rate in naturally bred mares.
Original languageEnglish
Article number104127
JournalJournal of Equine Veterinary Science
Publication statusAccepted/In press - 12 Sep 2022

Grant Number

  • 3-2018


Dive into the research topics of 'The correlation of endogenous progesterone concentration in diestrus on early pregnancy rate in Thoroughbred mares.'. Together they form a unique fingerprint.

Cite this