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Date:
September 1, 2007
INTRODUCTION
In the last 20 years there have been a few reviews
of camelid clinical pathology (Veterinary
Clinics of North America: Food Animal Practice,
1989, 1994) outlining the ways in which they are
similar to other mammals as well as some unique
features of these animals. We continue to learn more
about camelid hematology in general as well as some
ways in which alpacas and llamas differ.
Erythrocytes
Everyone is aware that erythrocytes from old and new
world camelids have a different shape than those
from other mammals. It is theorized that the size,
shape and hemoglobin concentration of camelid
erythrocytes play a role in increasing the
oxygen-carrying capacity as well as the ability of
erythrocytes to exchange oxygen. Camelid
erythrocytes have a lower MCV (22-29.5 fL) than most
other species, but a higher RBC count (10.1-17.3
million/l). PCV’s are similar to or slightly lower
than other herbivores (25-45%) and total hemoglobin
concentration in llama blood is high (11.3-19.0
g/dl) as compared to cattle. This is due to the
combination of a higher |
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concentration of hemoglobin in individual
erythrocytes (reference range for MCHC in the llama
is 39.8-46.2 g/dl and in cattle is 30.0-36.0 g/dl)
and the higher total RBC count. The high hemoglobin
concentration increases the ability of the cell to
carry oxygen while the small size and flattened
shape provide increased membrane surface for oxygen
exchange (higher surface/volume ratio). In
addition, it appears that camelid hemoglobin has
characteristics that allow a higher saturation with
hemoglobin at lower atmospheric oxygen pressure
(left shift in the oxygen dissociation curve). The
elliptical shape of the camelid erythrocytes also
makes them much more resistant to changes in blood
osmolality.
In addition to the elliptical shape of camelid
erythrocytes, other morphologic differences are seen
in normal animals. In many camelids, a small to
moderate number of hemoglobin crystals are present.
These darkly eosinophilic, rhomboid-shaped
structures are easily identifiable and appear to
have no clinical significance. Occasional camelid
erythrocytes have one or more elongated, pointed
extensions of their cytoplasm which extend from one
or both ends (often called dacryocytes, referring to
a tear - drop shape). These are rare in |
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