Supplementary corpora lutea monitoring allows progestin treatment interruption on day 70 of pregnancy in non-cyclic recipient mares.

This study looks at the impacts of interrupting a hormone treatment during pregnancy in non-cyclic mares. The results show that ending treatment on the 70th day allows for pregnancies to continue when certain hormonal conditions are met, and ceasing treatment at 120 days enables pregnancy continuation in all mares.

Introduction

• This research focuses on the impact of ending altrenogest treatment, a progestin, during the 70th or 120th day of gestation on maintaining a pregnancy in non-cyclic recipient mares. This means these mares are not going through regular reproductive cycles.
• The objective was also to correlate the findings of hormonal interruption with the number of supplementary corpora lutea (SCL) formations—a type of endocrine structure in female mammals which produces the hormone progesterone (P4)—and plasma P4 levels.

Methodology

• The study involved 25 mares, which were either in the anestrus (non-breeding), transitional or ovulatory phase.
• They were divided into groups based on the length of altrenogest treatment (70 days or 120 days), or their reproductive state when the treatment began.
• Throughout the study, the mares’ pregnancy status, SCL formation and P4 profile were closely monitored through ultrasonography and plasma progesterone testing.

Results

• The study found after interrupting hormone treatment, abortion only occurred in the group of mares that had treatment for 70 days (70ALT group).
• The study also found the days of first SCL formation were similar in the 70- and 120-day treatment groups and higher than the control group. Furthermore, the first SCL development period happened later during gestation in the anestrus group compared to the transitional or cyclic mares.
• Progestin synthesis in non-cyclic mares took place during a more advanced gestational period and portrayed a lower concentration during the 120 days compared to the cyclic mares.

Conclusions

• The research suggests progestin treatment in non-cyclic recipient mares can be halted at 70 days of gestation without causing abortion if SCL are observed, and at 120 days permits all recipient mares to continue their pregnancies.
• The timing of the first SCL development varied across different pregnancies and phases (anestrus, transitional and cyclic).
• The findings of this study enhance the understanding of pregnancy physiology and support the cessation of progestins treatment on the 70th day of pregnancy in non-cyclic pregnant recipient mares.