Factors affecting foal birth weight in Thoroughbred horses

Area of Science:

• Reproductive biology
• Equine science
• Animal reproduction

Background:

• Understanding factors influencing foal birth weight is crucial for equine breeding.
• Mare age, parity, gestation length, foal sex, and placental characteristics are potential determinants.
• Previous studies have explored these relationships with varying conclusions.

Purpose of the Study:

• To investigate the interrelationships among mare age, parity, gestation length, foal sex, placental weight, and foal birth weight in Thoroughbreds.
• To identify key factors affecting foal birth weight and their direct or indirect effects.

Main Methods:

• Analysis of foaling data from 348 Thoroughbred foals.
• Utilized path analysis to examine direct and indirect associations between variables.
• Included assessment of placental weight (allantochorion, amniotic membranes, umbilical cord).

Main Results:

• Placental weight positively correlated with foal birth weight up to a threshold of 6.5 kg.
• Above 6.5 kg, placental weight was not significantly associated with foal birth weight.
• Mare parity was directly associated with foal birth weight and indirectly through increased placental weight.
• Mare age and gestation length were not significantly associated with foal birth weight.

Conclusions:

• Placental weight up to 6.5 kg may be a rate-limiting factor for foal birth weight.
• Increases in placental weight beyond this threshold do not confer additional benefits to foal birth weight.
• The positive effect of mare parity on foal birth weight is mediated by placental development and other pathways.