Yes, dogs have placentas. Like nearly all mammals, dogs develop a placenta during pregnancy to nourish each growing puppy. But the canine placenta looks and functions differently from the human version, and it plays a unique role during birth that dog owners should understand.
How the Canine Placenta Is Structured
The dog placenta belongs to a category called “zonary,” meaning it forms a belt-shaped band of tissue that wraps around each embryonic sac rather than attaching as a single disc the way a human placenta does. This ring of contact tissue is where the exchange between mother and puppy happens. Every puppy in a litter has its own individual placenta, so a dog carrying eight puppies will produce eight placentas.
At a microscopic level, the canine placenta is classified as endotheliochorial. In practical terms, this means the developing trophoblast tissue (the outer layer of the embryo) invades the mother’s uterine lining until it directly surrounds her capillaries. Fewer tissue layers separate the maternal and fetal blood supplies compared to some other species, which allows for efficient transfer of oxygen, nutrients, and hormones. The placenta essentially acts as a temporary stand-in for the puppy’s lungs, gut, kidneys, and liver throughout the entire pregnancy.
When the Placenta Forms
After mating, the fertilized embryos float freely in the uterus for a period before settling into position. Implantation in dogs occurs roughly 18 to 20 days after the hormonal surge that triggers ovulation. Once the embryos attach to the uterine wall, placental tissue begins developing rapidly to establish that critical supply line between the mother and each puppy. From that point until birth, the placenta is the sole life-support system.
What a Dog Placenta Looks Like
If you’ve witnessed a dog giving birth, you may have noticed something surprising: the afterbirth has a distinct greenish-black color. This is caused by a pigment called uteroverdin, which forms as blood breaks down at the edges of the placental band. The green tint is completely normal in dogs and is one of the more unusual features of canine reproduction. You may also see dark green discharge during active labor, which comes from the same pigment and is not a sign of a problem on its own.
How Placentas Are Delivered During Birth
Canine labor has three stages: uterine contractions and cervical dilation, delivery of the puppy, and expulsion of the placenta. In dogs, the second and third stages overlap. Each puppy arrives still enclosed in or attached to its own placental membranes, and the placenta typically follows shortly after. Because dogs have a Y-shaped uterus with two “horns,” it’s common for two puppies to be born in quick succession from alternate horns, followed by two placentas.
Here’s the part that catches many first-time breeders off guard: mother dogs will rapidly eat the placenta if given the chance, often before you even see it delivered. This behavior is instinctive and seen across nearly all non-human mammals. Researchers believe it is part of the same suite of hardwired peripartum behaviors as nest-building, though some have proposed that hunger after fasting during labor also plays a role. If you’re trying to count placentas to make sure all were expelled, you’ll need to watch closely, because the mother can consume one in seconds.
Retained Placenta: What to Watch For
A retained placenta occurs when one or more placentas (or fragments of placental tissue) fail to be expelled after all puppies have been born. According to Cornell University’s veterinary faculty, in most cases where owners suspect a retained placenta, the dog has simply eaten it without being noticed. True retention is relatively uncommon, and when it does happen, the tissue is usually expelled on its own.
That said, retained placental tissue can occasionally lead to a uterine infection called metritis. Signs to watch for include:
- Continued straining as though still in labor, well after the last puppy has arrived
- Abnormal vulvar discharge that is foul-smelling or persists beyond normal postpartum bleeding
- Fever and lethargy developing in the hours or days after birth
A veterinarian can use ultrasound to evaluate the postpartum uterus. Retained fetal membranes show up as persistent dilation of the uterus with echogenic material inside, which looks different from the normal postpartum contents because it has a patchy, uneven pattern and doesn’t resolve on the expected timeline. Doppler imaging can also assess blood flow to former placental attachment sites, though this technique is less commonly used in routine postpartum checks.
How Dog and Human Placentas Compare
The biggest structural difference is shape. A human placenta is a single flat disc attached to one area of the uterine wall. A dog placenta wraps in a band around each embryonic sac. Humans also have a different level of tissue invasion: the human placenta is hemochorial, meaning fetal tissue is bathed directly in maternal blood. In dogs, the mother’s capillary walls remain intact, creating one additional barrier between the two blood supplies.
The functional job is the same in both species: deliver oxygen and nutrients, remove waste, and produce hormones that maintain the pregnancy. But the structural differences mean that canine and human pregnancies face different risks. Conditions like placenta previa, where the placenta covers the cervix, are a significant concern in human obstetrics but not a recognized issue in dogs, partly because the zonary band encircles the sac rather than attaching to one spot on the uterine wall.