LORI.feline

Feline placentation

Keywords: feline, placenta, anatomy

Feline gestation is approximately 64 days, starting about a day after breeding (cats are induced ovulators). Therefore, feline gestation is marginally longer than canine gestation.

Using body, crown-rump and head diameters from various published sources, the pregnancy below was estimated to be approximately 53 days of age. The first image serves as a key for the main image. Unfortunately, the manner in which the fetuses were arranged for photography suggests that they were somehow attached to one another. They were in fact, three separate fetuses.

Image size: 1000 x 87 px

In these specimens, the allantochorionic membranes of these fetuses were transected and everted (turned inside out), releasing the allantoic fluid from each fetus and exposing their internal chorionic surfaces (in reality, their allantochorionic surfaces because the allantois and chorion fuse as gestation progresses). The amnionic fluid remains within the amnions of the fetuses.

The gross anatomy of feline placentation is described as "zonary" and is described in greater detail elsewhere in LORI.

Image size: 4907 x 3456 px

Note the pellets of meconium; probably an indication of fetal stress. In advanced gestation, it is not uncommon to find yellowish amniotic fluid which in turn, has stained the fetus a yellowish color. Meconium is often found in the lungs of those fetuses as well.

Meconium staining is generally associated with fetal stress but a literature search will reveal that the pathophysiology is not at all clear. Fetuses with meconium staining are not always in state of acidosis and the overriding sympathetic tone associated with stress does not explain anal relaxation and increased peristalsis.

As shown above, the extra amnionic umbilical cord is not well defined in cats. The same is true of dogs as illustrated elsewhere in LORI. One could argue that these species do not even have extraamnionic cords. This is because the exocelom spreads out widely where the base of the exocelom and yolk sac remnant attaches to the placental zonary bands.

As mentioned elsewhere, the feline placenta does not have a green hematophagus border as is seen in canids. However, the mechanism for iron absorption appears to be similar in both species