Analysis of several factors of variation of gestation loss in breeding mares.

The research analyzed various factors affecting horse pregnancy loss, using ultrasound diagnosis files of mares in France for 3 consecutive years. The study identified both internal and external factors related to pregnancy loss, but found a low heritability rate of less than 5% in this trait, suggesting difficulty in selective breeding to prevent pregnancy loss.

Objective and Methodology

• The main aim of this study was to investigate the different factors contributing to pregnancy loss in mares.
• The researchers combined ultrasound diagnosis files of mares that were gestating for three years with the files of foal birth of these mares.
• A total of 28,872 gestations were included in the study, observing 2,898 pregnancy losses, providing a gestation interruption rate of around 9.12%.

Findings

• External factors contributing to the loss of pregnancy were the year and month of insemination, and the climatic conditions of the region.
• Internal or intrinsic factors contributing to pregnancy loss included breed of the father (heavier breeds had fewer pregnancy losses than the warm-blooded breeds), age of the mare (7 to 10 years had fewer losses), and the reproductive status of the mare (mares who had foaled less times lost fewer pregnancies).
• The likelihood of pregnancy loss increased with increased inbreeding or consanguinity.

Conclusions and Implications

• The research indicated a very low additive genetic effect, corresponding to a heritability below 5%. This suggests that the traits contributing to pregnancy loss are not strongly inherited.
• There were few identified environmental factors common to the offspring of the same mare, making it challenging to control these factors to reduce the risk of pregnancy loss.
• The study concluded that there is little hope of preventing gestation loss through selective breeding due to the very low heritability of the trait.

This study provided an insight into the complexity of gestation loss in horses, highlighting the role of multiple internal and external factors in this phenomenon. However, with the low heritability of the trait, the study also accentuated the challenges in preventing pregnancy loss in mares through selective breeding strategies.