INVOLUTION OF THE UTERUS
1. What is meant by involution? What events characterize involution?
2. What is “foal heat” in the mare?
3. Is postfarrowing estrus (3 to 5 days after farrowing) in the sow fertile or nonfertile?
The process by which the uterus returns to its nonpregnant size after parturition is known as involution.
The points of attachment of the fetal placenta to the endometrium slough and the exposed endometrium heals by forming new epithelium. In addition to new epithelial growth, the myometrium contracts and the cells shorten.Cow
Within 6 to 7 days postpartum, the upper two-thirds of the maternal caruncle sloughs into the uterus, becoming part of the fluids discharged. The epithelial cells of the caruncle must be shed for the placenta to be expelled. Within 21 to 35 days, all cellular repair has occurred and endometrial gland function is restored. The caruncles have retracted and cannot be palpated. Normally, estrus is observed in 45 to 60 days postpartum. Suckling by the calf, low energy intake, infections, and heavy lactation delay estrus.
Mare, Ewe, and Sow
Involution in the mare is rapid, but not complete, by the time of foal heat, which occurs within 6 to 13 days postpartum. Foal heat is usually accompanied by ovulation and mares bred at this time can become pregnant. However, conception rates are lower when breeding occurs during the foal heat.
In the ewe and sow, about 24 to 28 days are needed for complete involution. In the sow, a nonfertile (no ovulation) estrus occurs 3 to 5 days after farrowing. Estrus combined with ovulation is usually inhibited throughout lactation. Sows not nursing their litters during the first week after farrowing have estrus with ovulation within 2 weeks. Weaning of pigs at any time induces estrus with ovulation in 3 to 5 days.
Resumption of estrus in the ewe and mare is consistent with the photoperiod of estrous activity characteristic for these species.
Bitch
The interplacental areas return to normal within a few weeks, but the placental sites require about 12 weeks to involute and heal. Estrus usually does not occur until after the young are weaned.
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