Monitoring ovarian function and pregnancy by evaluating excretion of urinary oestrogen conjugates in semi-free-ranging Przewalski’s horses (Equus przewalskii).

This study examines how the reproductive hormone levels of Przewalski’s horses can be tracked through the analysis of daily urine samples, providing insights into their ovarian function and pregnancy. Urinary oestrogen levels were analyzed during various stages of reproduction, and this method proved effective in identifying various reproductive events in these horses.

Methodology and Key Findings

• The research involved collecting daily urine samples from eight Przewalski’s mares, roughly equating to five samples per week. These mares were maintained in semi-free-range pastures.
• High-pressure liquid chromatography was used to ascertain the relative percentage contributions of immunoreactive urinary oestrogens during different reproductive stages. These include oestrus (regular reproductive cycle), the luteal phase (post ovulation), early, mid- and late gestation (pregnancy).
• The results showed that the onset of the oestrus cycle aligned with increasing day lengths, with an average non-conception cycle lasting around 24.1 days. Most copulations occurred between four days prior and one day after the peak in preovulatory oestrogen levels.
• The study also looked at the gestation length in horses, observing a mean gestation length of 48.6 weeks. During pregnancy, the excretion of oestrogen conjugates in the urine increased around 300-fold compared to non-pregnant mares. This peak was most notable by week 24 of the pregnancy.

Implication of the Findings

• The study demonstrates a way to monitor longitudinal reproductive events in Przewalski’s mares (such as their regular reproductive cycles and pregnancy) through the evaluation of urinary oestrogen conjugates. This is essential for conservation purposes, breeding programs, and studies focusing on equine reproduction.
• The ability to monitor and thereby predict and follow various phases of reproduction in these animals can help maintain their numbers in wild and semi-wild environments. It could also potentially improve care in captive environments.
• Aside from providing an effective non-invasive monitoring method, these findings can also contribute to scientific understanding of Przewalski’s horse reproductive biology.