Hematology of Camelids

Susan J. Tornquist, DVM, PhD, DACVP

Susan.Tornquist@oregonstate.edu

College of Veterinary Medicine, Oregon State University

Corvallis, Oregon

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/ml). 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 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 normal camelids, but may occur in high numbers in camelids with severe anemia of a variety of etiologies.

Because of the small size and unique shape of camelid erythrocytes, laboratories may have to adapt their techniques when counting them. Manual methods (eg, Unopettes and hemacytometers) are accurate, but if automated instruments are used, threshold settings on these instruments must be adjusted for llama erythrocytes. Single-channel electronic counters with threshold set at 5–8 fl appear to be the most appropriate instruments for counting llama erythrocytes. This low threshold setting allows detection of microcytic erythrocyte populations while excluding most platelets from being counted as erythrocytes. Indices derived from multichannel analyzers may be inaccurate if calibration adjustments are not made. In general, hematocrit and hemoglobin methods which are valid in other species work well with llama blood.

Anemia

Moderate to severe anemia is a relatively common problem in alpacas presented to referral institutions and in those seen in private practices. The anemia is, at times, unexplained, and can be very debilitating. As with other species, it’s important to try to classify an anemia in order to determine the underlying cause and possible treatment. Classification of anemia as regenerative or non-regenerative is particularly helpful in looking to the bone marrow (if non-regenerative) or elsewhere (if regenerative) as the cause of anemia. This is made more difficult in camelids, by the fact that they appear to have more unpredictable regenerative responses to anemia than some other species.

In llamas that experienced an acute loss of up to 50% of their blood volume, reticulocyte counts increased but seldom rose above 1% despite the fact that hematocrits in these llamas rose steadily. It would appear that the reticulocyte response in llama is intermediate between that of the horse and those of other domestic animals. In these experimental llamas, moderate increases in anisocytosis and polychromasia were noted. These llamas also had increased numbers of nucleated erythrocytes which varied from 3–27/100 WBC in all but one llama. This one llama had a marked increase in nucleated erythrocyte count (up to 223/100 WBC) but did not have similar magnitudes of increase in polychromasia or reticulocytes.

A recent study at Oregon State University used a model of induced acute, severe, normovolemic anemia (less than 15% PCV) in otherwise normal, healthy alpacas. Although the number of animals in the study was low, the results suggest that alpacas are similar to llamas in that they produced reticulocytes and that the reticulocyte response never rose above 1.5%. The average number of days to a detectable reticulocyte response was 2.6 with the peak of reticulocyte numbers occurring at an average of 10.4 days after induction of anemia. Thus, anisocytosis, polychromasia, nucleated RBCs, and reticulocytes do occur in camelids as part of a regenerative response, but are not very predictable in terms of their magnitude. This makes it difficult to assess the degree of regeneration without examining multiple blood samples in a consecutive manner.

Interestingly, several of the alpacas in the study showed mild regeneration but had not returned to a normal PCV 2–3 months after the episode of acute anemia. As these were normal, healthy animals when acute anemia was induced and were not known to have any other reason why they wouldn’t adequately respond to anemia (e.g. they were negative for M. haemolamae, and not iron deficient) it raises the question whether acute anemia may be associated with a new “set point” in this species. More work, on greater numbers of alpacas, needs to be done to answer this question.

Oxyglobin study

With funding from the Alpaca Research Foundation, we performed a small clinical trial to determine any possible adverse effects of polymerized ultrapurified bovine hemoglobin (PUBH) blood substitute in alpacas. Our overall hypothesis was: Administration of PUBH to anemic, normovolemic alpacas will result in improved clinical and hemodynamic parameters without adverse effects on hemostatic, renal, or liver parameters. The questions we hoped to answer with this study were: 1) whether adverse effects are seen with administration of PUBH to anemic alpacas, 2) whether there is an improvement in clinical and laboratory parameters in these alpacas and 3) whether PUBH works significantly better than hetastarch, a colloid plasma expander, in normalizing these parameters.

The study included 6 normal healthy adult alpacas. After baseline information was obtained, two jugular catheters were placed. The alpacas had approximately 1 liter of blood removed daily for 3 consecutive days. The plasma was separated and re-transfused into each alpaca. When a PCV of less than 15% was achieved, the alpaca was given either PUBH or an equal volume of hetastarch intravenously. Samples were taken at times 0, 30, 60, 90, and 120 minutes post-treatment and once a day for 5 days post-treatment. Tests performed included body temperature, pulse, respiratory rate, CBC, PT, PTT, chemistry panel, blood gases, and central venous pressure measurement.

No adverse effects were found on hematologic, liver, renal, or coagulation parameters. Significant differences between effects of hetastarch and PUBH administration were not found. PUBH appeared to be associated with increased O₂ offloading to tissues.

Mycoplasma haemolamae

An effective antibiotic treatment that consistently clears M. haemolamae infection (including the carrier state) has not been proven. Injectable and oral enrofloxacin and injectable florfenicol did not show any efficacy in controlled studies. Injectable oxytetracycline given subQ every 3rd day for 5 treatments shows the most efficacy in clearing detectable organism, but does not usually totally clear the carrier stage. There is no scientific evidence to show that feeding tetracycline-treated feed or pellets would be equally or more effective in clearing infection.

A current study is examining the immune responses of an alpaca who appears to have resistance to infection with M. haemolamae. Comparison of this animal’s immune responses to those of other, non-resistant alpacas, may be important in showing how infection can be prevented.

REFERENCES

Garry F, Weiser MG, Belknap E. Clinical Pathology of Llamas in Vet Clin N America: Food Animal, 1994.

Garry F. Clinical Pathology of Llamas in Vet Clin N America: Food Animal, 1989.

Morin DE, Garry FB, Weiser MG. Hematologic responses in llamas with experimentally induced iron deficiency anemia. Vet Clin Pathol. 22:3, 81-86, 1993.

Morin DE, Garry FB, Weiser MG, et al: Hematologic features of iron deficiency anemia in llamas. Vet Pathol 29: 29: 400-404,1992.

Tornquist SJ, et al Vet Path 2002. 39: 616.