CHAPTER 37: DISEASES OF GESTATION AND PARTURITION
Introduction
is the period where the fetus develops inside the uterus of the mare. The gestation period last approximately eleven months, or an average of three hundred and thirty- five days. Foals born at three hundred to three hundred and twenty days are considered premature while foals born after three hundred and sixty days are postmature. To determine if a mare is in foal either a rectal exam or ultrasound can be done to confirm pregnancy. A vet can also determine how old the embryo/fetus is.
In the horse gestation is divided into three sections or trimesters:
During the first trimester the embryo embeds in the wall of the uterus and begins to form. By day twenty-five, the fetal is present indicating that organogenesis has occurred. The endometrial cups form around day thirty and the sex of the fetus may be discernable by fifty-eight days. Fetal growth is slow during the first trimester and seems to plateau. By the end of the first trimester the fetal viscera are formed. During the second trimester the fetus grows and fine structures such as around the lips, eyes, nose and tail and the hooves are formed. By the end of the second trimester the fetus is fully formed with hair on most of its body. The third trimester is characterized by fetal . During the last one hundred and ten days of gestation the foal increases in size by fifty percent. is the expulsion of the fetus and the fetal membranes from the uterus through the cervix and the vagina. It is commonly called “foaling” or “giving birth”. Parturition is divided into three stages in mares: Stage one is the preparatory stage. During this time the mare is experiencing hormonal changes to prepare for foaling and the fetus is position itself in the uterus for expulsion. The mare may seem during this stage and may repeated lie down, look at her abdomen, urinate frequently, roll, sweat or pace her stall. Stage one ends with the rupture of the membrane at the cervical star. This is commonly referred to as the “water breaking”. Stage two is characterized by the expulsion of the foal. This stage should involve - , minutes of forceful straining and contractions. The foal should present at the vagina inside the intact amniotic sac and should emerge with the head tucked between the forelimbs. The umbilical cord should remain attached until the mare rises and should not be removed. Stage three is characterized by the expulsion of the . The placenta should be expelled within four hours of expulsion of the foal and should be expelled intact. Examination of the expelled placenta to ensure it is whole should be done as soon as possible.
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