The relationship between consecutive pregnancies in Thoroughbred mares. Does the location of one pregnancy affect the location of the next, is this affected by mare age and foal heat to conception interval or related to pregnancy success.

The research article explores the relationship between consecutive pregnancies in Thoroughbred mares, particularly looking at how the location of one pregnancy might influence the location of the subsequent one, and how this might be affected by factors such as the mare’s age and interval from foaling to conception and its correlation with pregnancy success.

Research Methodology

• The study aimed to:
  • Determine the location of concepti in consecutive pregnancies
  • Investigate whether this location changes with the age of the mare or the interval from foaling to conception
  • Explore whether the location of the new pregnancy relative to the previous one impacts the success of pregnancy
• To collect data for these research objectives, 1383 Thoroughbred mares were monitored, using ultrasonic scanning during oestrus and early pregnancy.

Research Findings

• More pregnancies were located in the previously non-gravid horn (PNGH, the part of the uterus that was not carrying the last pregnancy) – 79.2%, significantly more than in the previously gravid horn (PGH, the part of the uterus that was carrying the last pregnancy) – 20.8%.
• The number of pregnancies located in the PGH significantly increased with the mare’s age and the interval from foaling to conception. This suggests that as mares get older, and the interval between birthing and conception reduces, pregnancies are more likely to be located in the PGH.
• Significantly more pregnancies located in the PGH failed as compared to those in the PNGH. 16.5% of pregnancies in the PGH failed, while only 4.6% of pregnancies in the PNGH failed.
• Most pregnancies were more successful when located in the PNGH. Thus, the higher mortality rates in older mares and those with shorter foaling to conception intervals (those more likely to have a pregnancy in the PGH) could be due to more pregnancies being located in the PGH.

Study Conclusions

• Based on their findings, the researchers suggest that breeding older mares on alternate years and maximizing the foaling to conception interval could improve their reproductive success. This may allow more pregnancies to occur in the PNGH, which shows higher success rates according to the study.
• Another recommendation based on the study’s findings is that termination of pregnancies located in the PGH followed by timely recovery might be justifiable, as it could lead to less pregnancy failure. Similarly, Embryo Transfer (ET) might be advisable in older mares covered close to foaling, shifting the pregnancy’s location from the PGH to a surrogate mare’s uterus.