Horses have been giving birth unassisted a lot longer than we’ve had them in captivity and insisted on being around while the mare is foaling. Often they foal unexpectedly out in a paddock, leaving little chance of examining the afterbirth the following morning.
If you are able to be around for the birth, having prepared the mare to foal, you should have access to viewing the afterbirth.
The afterbirth is made up of the amniotic sac (the foal was delivered in this), the hippomane (a salty build up) and the placenta. If given the opportunity to inspect, certain characteristics of the placenta can provide information regarding health of the mare and foal.
Entirety of the Placenta With Only One Hole
The placenta when laid out should be in a T or Y shape, showing the body of the placenta and the two uterine horns. When the foal is in utero it is positioned in the body of the uterus as well as into one of the horns. Generally one of the horns of the placenta will be thicker while the other appears quite thin.
The thicker of the two is the pregnant horn where the foal was located while the thinner is known as the non pregnant horn.
There should be only one hole in the placenta where the foal exited. This is known as the cervical star, the point at which the placenta ruptures to allow the allantoic fluids to be released (breaking of the mare’s waters).
If the placenta fails to rupture, this is deemed a red bag delivery. Here the cervical star is visible, showing where the placenta should have broken, releasing the mare's waters.
If there is more than one hole in the placenta, it may be difficult to distinguish that the placenta has been expelled from the mare in its entirety. There are often holes in the non pregnant horn of the placenta due to this tissue being thinner and easier to tear. If there is to be any retained placenta in the mare, it is likely to be from the non pregnant horn.
Retained placenta of any size can lead to infection in the mare, laminitis and even death. If you suspect that the mare has retained placenta it is worth seeking out a vet. A vaginal discharge after foaling that appears white or mucous-like could further indicate infection due to retained placenta.
The Colour of the Placenta
Normally when a placenta is turned inside out after the mare has foaled; it should be a deep to bright red. Colours outside of this – often brown or green – indicate that there was infection inside the mare which could have affected the amount of nutrients provided to the foal while in utero.
The Weight of the Placenta
A general rule of thumb for horses is that the foal should be a tenth of the mare’s weight and the placenta a tenth of the foal’s weight. For an average Thoroughbred foal, this should mean a placenta of around 4.5-5 kilograms or 10-11 pounds.
A placenta that is heavy also indicates infection which could have compromised the foal while a placenta that is underweight indicates malnutrition possibilities with regards to the foal.
Noting any abnormalities with regards to holes, weight and colour of the placenta allows the horse owner to be aware of potential problems that may arise with the newborn foal or recent mother. Making a note of such information may assist the vet should health problems arise for either of the pair shortly after foaling.
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