LORI.camelid

Camelid placentation; the llama

Keywords: Llama, camelid, placenta, anatomy, parturition.

Note: The term chorioallantois is commonly accepted and is seldom hyphenated i.e. chorio-allantois. However, terms such as chorio-amnion and amnio-allantois are not commonly used. Therefore they have been hyphenated in this entry to clarify their composition.

Placentation in the llama (and all camelids) is a source of fascination for those who are familiar with the placentation of horses and cattle. In a manner of speaking, it is a hybrid of both, yet distinctly different. The camelid chorion is similar to that of horses i.e. diffuse and epitheliochorial. Although the two look similar macroscopically, llamas have small, rugaevilli (squat projections with folded or ridged surfaces) rather than the microcotyledons seen in horses. The superficial appearance of a llama placenta is seen below. Note too, how small areas of the chorion are devoid of rugaevilli. Local absence of microcotyledons is a common feature of equine placentation as well. In both horses and camelids, these are normal and probably occur where the chorion has folded on the endometrial surface.

Fig 1. Image size: 1122 x 791px

The internal structure of camelid placentation (illustrated in the next image) is very different to that of horses. In horses, the amnion is separated from the chorion completely i.e. it is "a balloon within a balloon". The fetus lies within the central balloon (the amnion) tethered to its inner surface by the intra-amnionic cord. The central "balloon" is then tethered to the chorion by the continuation of the umbilical cord (minus the urachus) i.e. the extra-amnionic cord. See this entry and another, illustrating the equine anatomy elsewhere in LORI. Readers will note that the allantois in horses lines the space surrounding the amnion, separating it completely from the chorion. This explains why there is no such structure as an amnio-chorion in horses. Yet, that label appears in the image of the llama placenta shown above. This is because the allantois in camelids lies adjacent to the amnion; it does not surround it. This is similar to the situation in cattle where the allantois also lies adjacent to the amnion and does not surround it either. In both camelids and cattle therefore, there is a section of the amnion that lies against the chorion and this is the amnio-chorion. See figure 2

Fig 2. Image size: 2732 x 1835 px.

During foaling and calving, the chorioallantois ruptures and a large amount of fluid escapes from the vulva before the amnion appears at the vulva lips.  This is because the chorioallantois abuts the internal cervical os in horses and cattle. Although the chorion also lies against the internal cervical os in camelids, it is the amnion, not the allantois, that lies adjacent the chorion in this area. See figure 2. Therefore, when the chorion ruptures in camelids, the allantois does not rupture at the same time. As a result, large volumes of allantoic fluid are not discharged before the amnion become visible at the vulva lips. Instead, the allantois its bypassed by the fetus in its amnion although a large area of the amnion is still attached to the allantois over an area known as the amnio-allantois. See figure 2. The transparent amnion pushes through the cervix and soon appears at the vulva lips, the fetus visible within.

After the fetus has been born, the bluish allantoic fluid can be seen within the chorion, at the vulva lips, yet to be expelled. The allantois is visible through the wall that was formed by the fusion of the amnion and allantois i.e. the membrane mentioned in the previous paragraph, the amnio-allantois (see Fig 2&3).

Below, a dead fetus (washed and devoid of its epidermal membrane) placed within the opened placenta to show the relationship between the fetus and the fetal membranes:

Fig 3. Image size: 990 x 616 px.

Notes  Although ovulation occurs with equal frequency from both ovaries, the fetus almost always lies in the left uterine horn (see figures 2 & 3). Also, camelids are like horses, with the vast majority of births in cranial, longitudinal presentation and dorso-sacral position. Normal posture is the same as for cattle and horses.  In brief, parturition takes place in the morning and the female usually stands throughout second stage. Second stage is usually completed within 20 minutes but takes significantly longer in primipara. The placenta is usually expelled with the chorion on the outside but occasionally, inside out.  As for all herbivores, hippomanes are occasionally found within the allantois. Although there is one report of hippomanes in the amnion, this seems unlikely; perhaps a feature of errant handling of fetal membranes during inspection.

Selected references

Fowler M.E. and Olander H.J.  1990. Fetal membranes and ancillary structures of llamas (Lama glama) Am.J. Vet. Research. 51: 1495-1500

Fowler M.E. 2011. Medicine and Surgery of Camelids.  John Wiley & Sons. ISBN: 0470961694, 9780470961698

Morton. W.R.M. 1961 Observations on the full term foetal membranes of three members of the camelidae (Camelus dromidarius L. Camelus bactrianus L. and Lama glama L)

J. Anatomy 95: 200-209