Science Reviews - Biology, 2023, 2(2), 21-29 Ananya Bhattacherjee

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Avian Erythrocytes and Agranulocytes - a Review

Ananya Bhattacherjee, PhD

Independent Researcher, Bhubaneswar, India; ananyabhattacherjee@gmail.com

such as rheas, emus, ostriches, chickens, and geese. Though all of them have the typical avian similarity in blood

cells, yet there are some differences. Along with normal and mature erythrocytes, lymphocytes, and monocytes,

the present study also focuses on rubricytes, reticulocytes, poikilocytes, polychromatophilic erythrocytes,

reactive lymphocytes, pleomorphic monocyte nuclei, etc.

Keywords: Erythrocytes, lymphocytes, monocytes, blood cells, hematology, birds, Aves, morphology

Birds inhabit a vast area from sea to mountains and

deserts to rainforests. Their physiology differs

based on habit, habitat, age, sex, feed, and breeding

bocytes which are equivalent to mammalian plate-

lets. There are two types of leukocytes, viz., agran-

ulocytes and granulocytes. Agranulocytes are of

two types, namely, lymphocytes and monocytes.

Granulocytes are of three types, heterophils same as

neutrophils in mammals, eosinophils, and baso-

phils. In the following paragraphs, facts about avian

erythrocytes and agranulocytes are discussed.

et al., 2011 and Lazăr et al., 2012). Such red blood

cells (RBCs) are more efficient than spherical ones

of the same volume. Aves are the most active verte-

brates and have a high metabolic rate. Due to this,

the demand for gaseous exchange is higher than

other animals. Among Aves, aquatic birds have a

higher metabolic rate than terrestrial birds. As a re-

sult, their erythrocytes are larger so that sufficient

gaseous exchange can take place as reported by

Hartman and Lessler, 1963. Nucleated RBCs of

chicken (terrestrial bird) and White Embden goose

(aquatic bird) performed by Tripathy and Acharya,

2019, reported that both red blood cells and their

nuclei in geese are larger compared to chickens. The

measurement of a bird’s RBC ranges from 11-16μm

in length and 6-10μm in breadth. Among birds,

Rheiformes bear the largest blood cells. Their RBCs

stain orange-pink with deep purple-colored nu-

cleus (Gallo et al., 2015). Samour et al., 2010 noticed

that the dimensions of peafowl RBCs are

densely populated clumps of condensed chromatin

surrounds the central loosely arranged chromatin

(Khan et al., 2016). Dimensions of erythrocytes de-

crease with an increase in age as nuclear chromatin

Ananya Bhattacherjee Science Reviews - Biology, 2023, 2(2), 21-29

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condenses as mentioned by Kramer, 2015 and Khan

et al., 2016. Macrocytes, microcytes, and anisocytes

reflect changes in the size of erythrocytes. These can

be observed in mono-layer blood film and the de-

gree of anisocytosis can be determined by the pres-

ture erythrocytes with circular nuclei. They have a

very thin ring-like basophilic cytoplasm around the

nucleus. Like this, other immature RBCs are me-

tarubricytes or polychromatic erythroblasts. These

cells are less circular with basophilic and more

abundant cytoplasm than rubricytes in the case of

Rhea. The nuclei of such cells are round with par-

tially condensed nuclear chromatin. Young poly-

chromatic erythrocytes were also observed in Rheas.

They are slightly oval with a larger non-basophilic

smear of birds, but if present in large numbers may

indicate any neoplastic process, viral infection, or

genetic disorder. (Gallo 2015).

Immature erythrocytes are also known as reticulo-

cytes which have a distinct ring of aggregated retic-

ular material (reticulofilamentous substances) cir-

cling the nucleus (Khan et al 2016). Chickens and

turkeys have a greater number of reticulocytes in

peripheral blood compared to mammals. These au-

thors also observed more polychromasia in young

plastids (Haile and Chanie, 2014 and Wakenell,

2010).

Round immature erythrocytes are also noticed in

emus but with an irregular nuclear periphery. The

mature RBCs which differ from typical oval shapes

are called poikilocytes, such as schistocytes and

dacryocytes. Schistocytes are erythrocyte fragments

with two pointed ends found in peripheral blood.

These fragments form when RBCs have to cross

triches, the centrally located reticulocyte nucleus

contained reticular chromatin without nucleolus.

The cytoplasm of erythrocytes was light blue to

gray. These were oval-shaped but smaller and with

wider nuclei compared to mature erythrocytes.

Like rubricytes, small number of polychromato-

philic erythrocytes are sometimes present in avian

blood smears. These cells are the last stage of ma-

ture erythrocyte development. The cytoplasm of

such cells has more ribosomal RNA and appears

served. These cells are paler compared to mature

erythrocytes and have an area of cytoplasmic pallor

covering more than half of the cytoplasm. These

cells have vacuoles and their nuclei are pyknotic

(Campbell, 2012).