In the business of breeding mares it is important to maximize the number of foals a dam produces. On top of this many breeds reward for having foals born as early as possible in the calender year. Because of this mares who are not caught early in the year may be allowed to go barren to back up the foaling date. Barren years result in economic loss because of expense for feed and housing, transportation, animal care, and no productive breeding fees. The major impediment to reaching this goal is the long gestation period, approximately 340 days. This means that to produce a foal at yearly intervals and at about the same time of year you only have 25 days to get the mare settled. This articles discusses examination of the mare in the postpartum period and breeding on the foal heat.

In some studies the pregnancy rate of breeding on the first postpartum estrus, the foal-heat, is often 10%-20% lower than that achieved by breeding on subsequent estrous periods. When foal heat is missed the result is a shift to the next foal being born 15 - 20 days later the following year. By understanding the events in the postpartum mare and how they affect fertility you can optimize your chances at successful early breeding. The normal postpartum events in chronological order are:

• 1st 3 hours: Placenta released
• 1st day: marked decrease in uterine size, small amount of bloody discharge from vulva.
• 2nd day: decrease in discharge and changes from bloody to a muddy brown.
• 3rd to 5th day: gravid horn still more enlarged than nongravid horn; vulval discharge ceases; On speculum exam blood-tinged discharge noted at cervix; Cervix is hyperemic
• 5th to 15th day: first estrus (foal-heat); gravid horn still more enlarged than nongravid horn; blood-tinged discharge may still be evident at cervix; Cervix may still be hyperemic; Cervix does not close from time of parturition until after foal-heat ovulation occurs.
  • 43% of mares ovulate by day 9
  • 93% by day 15, and 97% by day 20
• 1st month: Uterine horns return to pregravid size by day 32 postpartum.

We do not understand well the mechanisms that return the uterus to a normal state. Uterine contractility may play an important role in rapidly reducing the postparturient uterus to its pregravid state. Concurrent with this decrease in uterine size, significant lochial fluid is discharged from the uterine lumen, reverting to a condition more conducive to embryonic support.

Histologic character of the endometrium uterine involution has been studied and the progression of events are:

• Resorption of microcarunicles is essentially complete by day 7 postpartum and overlying lumenal epithelium is intact by days 4-7 postpartum.
• Endometrial gland dilation is absent by day 4 postpartum and glandular activity increases, as indicated by taller epithelial cells with increased mitotic activity, to day 12 postpartum.
• The endometrium usually has a normal pregravid histologic appearance by day 14 postpartum.