Seasonal absence of supplementary corpora lutea in pregnant mares and the relationship with pregnancy loss.

This study investigates the impact of conception season on the development of supplementary corpora lutea in pregnant mares, and examines a possible relation with rates of pregnancy loss. The research indicates that the development of these structures in pregnant mares is influenced by the season in which conception takes place, but their absence does not increase the risk of pregnancy loss.

Objectives and Method of the Study

• The motive of the study was to analyze the effect of the season of conception on the formation of supplementary corpora lutea (SCL) and its relation to pregnancy loss in mares.
• Two experiments were carried out in different hemispheres – the Northern (UK) and Southern (Brazil).
• In the first experiment, 199 pregnancies were followed from day 14 till full term. These pregnancies were used to determine the count of SCL and viability of the pregnancy.
• The breakdown of these 199 pregnancies was as follows: 178 were conceived during the breeding season (March-September) and 21 in the non-breeding season (October-February).

Findings of the Study

• Pregnancies from the breeding season had a higher likelihood (75.8 %) to develop at least one SCL as compared to pregnancies from the non-breeding season (33 %).
• However, the study also implied that the presence or absence of SCL does not significantly affect the pregnancy loss rate among mares. The study noted that instances of loss from day 35 to day 120 of pregnancy in mares, regardless of the existence of SCL, were not statistically different.

Further In-depth Analysis

• In the second experiment held in the Southern Hemisphere, the research team categorized the recipient mares into three groups based on their ovarian activity at the time of embryo transfer. The groups were – Anestrus, transitional and cyclic.
• It was discovered that all transitional and cyclic mares developed at least one SCL, whereas only half of the anestrus recipients developed SCL by the 120th day of gestation.

Conclusions Drawn

• Based on the findings, the study concluded that the formation of SCL in pregnant mares is influenced by the season of conception. This suggests that it is regulated by the photoperiod and the endogenous seasonal fluctuation in gonadotropin concentrations.
• Also, mares without SCL were not at an increased risk of pregnancy loss, thereby implying that absence of SCL does not contribute to pregnancy loss.