University of wisconsin-madison

Principles of Parturition

The day of parturition is in general decided by the fetus. It has to do with fetal maturation and growth. Eventually the fetus exceeds the ability of the placenta to supply it with oxygen and nutrients, and remove waste products. The fetus responds by releasing a series of hormones that culminates in cortisol release from the fetal adrenal gland. This cortisol initiates the parturition events causing decreases in placental progesterone and an increase in maternal PGF2a which initiate contractions. The initial contractions are followed by oxytocin increases to cause the major contractions once the fetuses head enters the cervix.

Although the day of parturition is determined by the fetus, the time within that day is determined by the mare. As described before, mares will generally foal at night. In particular they seek a quite place to foal. Lights that are kept on after labor has begun appear not to have any affect on the time of parturition. This enables the video observance of parturition. As little distrubance of the mare as possible is recommeded as the mare can delay the first part of labor until she feels safe or comfortable.

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