Maternal parity affects placental development, growth and metabolism of foals until 1 year and a half.

The study investigates the effect of a mare’s parity, or the number of times she has given birth, on placental development, foal growth, and metabolism up until one and a half years post-birth. Results indicate that first-time (primiparous) mares produce smaller, less mature foals with altered metabolism compared to experienced (multiparous) mares.

Research Methodology

• Twenty multiparous mares (older than six years) and twelve primiparous mares (up to five years old) were artificially inseminated using the same stallion. The pregnancies were similarly monitored.
• At birth, the foals and placentas were measured, with placenta samples taken above the umbilical cord as well as in the pregnant and non-pregnant horn for stereological analyses.
• The foals were weighed and measured up to 540 days post-birth. Glucose tolerance tests were done at 120 and 360 days. At 360 days, male foals were castrated and their testicular maturation was analyzed using RT-qPCR.

Research Findings

• Primiparous mares produced lighter and smaller foals and placentas. The ratio of foal birth weight to placental surface area was lower in this group compared to the multiparous group.
• These foals remained lighter than their multiparous counterparts up until 360 days and smaller until at least 540 days.
• At 120 days old, the foals from primiparous mares had a higher glucose tolerance than those from multiparous mares, suggesting lesser maturity in terms of controlled glucose homeostasis.
• At 360 days, the testicles of prepubertal foals from primiparous mares were less mature compared to those from multiparous mares.

Conclusion

These results suggest that primiparity in mares results in smaller, less mature offspring with altered metabolic processes that persist until at least 540 days post-birth. This can potentially impact their future sporting career, especially if it begins at an early age. This study calls for more attention on the influence of maternal parity on post-natal growth and metabolism, particularly when it comes to horse breeding for specific purposes, such as racing.