The placenta is the critical lifeline between the mare and foal. In mares, the placenta is attached on its outside surface to the wall of the uterus through millions of microscopic finger-like projections called villi that link like Velcro to millions of the same on the inner surface of the uterus. Nutrients are exchanged between mare and foal through these attachments. A normally functioning placenta is thus required for the birth of a healthy foal at full term.
Most mares pass the placenta within 30 minutes of foaling and it should be passed within 2 hours of foaling. A placenta is considered retained if it has not passed within 3 hours of foaling. It is critical that there not be any retained placenta left in the mare. This can cause life-threatening infection and must be discovered and removed right away.
There is important information contained in the shed placenta. When possible, save it for your vet to evaluate. Place the placenta in a bag in a cool place for your vet to examine. I lay the placenta out flat in an “F” shape with the white, glistening side out (allantois). The most common area for tears is the tip of the uterine horns, especially the wrinkled non-pregnant horn, which need to be examined closely.
I evaluate the overall size and weight of the placenta. I assess it for completeness and look for both uterine horn tips. If there are tears in the placenta, was this from being stepped on, or is there a piece of placenta still in the mare? I then turn the placenta inside out and look at the velvety red chorionic surface, looking for evidence of thickening or other abnormality. That is the side that is stuck like Velcro to the inside of the mare’s uterus during pregnancy and releases after foaling.
A little thickening toward the tip of the horns is normal. Small pale patches on the red surface are normal. A floppy, meaty olive colored mass separate from the placenta is normal and is called a hippomane. It is a concretion of waste products that forms inside the allantoic sac with the foal.
Ensure that the entire placenta has been passed.
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