There are 3 anatomical sites on the elephants body where blood can be collected:
One of the ear veins (or arteries for arterial blood sample)
One of the branches of the saphenous veins (hindlegs)
Cephalic vein (front legs)
How to collect a blood sample:
Most elephants can be trained for this procedure using positive reinforcement training. If not trained, standing sedation (or general anesthesia) in case of free ranging elephants) will be required. When alpha-2 agonists are used , vasoconstriction may hinder the access to the ear veins, especially in young calves. Combining alpha-2 agonists with butorphanol may help to increase the filling of these veins.
When the environmental temperature is low, the ear veins may collapse. Flushing the inner side of the ear with large amounts of warm water (or packing the area with heated bean or rice bags) can increase the filling of these veins.
The collection site should be clean and dry before blood is collected.
Ear veins: press firmly on the site where you can see the shape of the vein. Press until you see the vein becoming larger in diameter. Use a small butterfly needle and collect the blood in a vacuum blood tube. If not available, you can use a small needle (23G) and a syringe and empty the syringe in the blood collection tube after removing the needle. To avoid damaging the blood cells (hemolysis), the tube should be filled slowly while flushing the blood carefully against the wall of the tube, that is slightly tilted.
Saphenous and cephalic veins: these veins are larger in diameter than the ear veins, but covered by a thicker skin. A 19G or 21G needle (preferably connected to a vacuum tube) can be used and should be inserted perpendicular to the skin.
Indication of the blood cellection sites on the front leg (left photo, Vena cephalica) and the inner side of the hind leg (middle and right photo, Vena saphena).
Blood cellection from the inner side of the ear using a butterfly needle and vaccum tube.
Blood cellection from the inner side of the hind leg of a well-trained adult Asian elephant bull using a vacuum bottle for collecting large amounts. Courtesy: Rotterdam Zoo
This chapter includes a lab manual that was developed for a Healthcare and Welfare Workshop for elephant veterinarians given in Myanmar in 2018, organized by Elephant Care Asia (an initiative or elephant Care International - http://elephantcare.org/.
Erythrocytes in elephant whole blood EDTA samples can best be counted on an automated blood cell analyzer.
Such an analyzer automatically measures the hematocrit. After centrifugation of the blood sample, a plasma evaluation should always be performed.
The morphology of the erythocytes should be examined microscopically in a (preferably fresh) blood smear, stained with Wright-Giemsa.
If no automated cell counter is available, manual erythrocyte count is a second option.
Total white Blood count (WBC):
Automated analyzers have limited value in elephant hematology. However, they can be used to measure the total amount of white blood cell. Automated cell counters come in several forms. Those used for other mammalians can only be used for total WBC in elephants.
Manual WBC count can be done using a Hemocytometer Counting Chamber.
Differential White Blood Cell (WBC) count:
Automated analyzers cannot be used to differentiate the white blood cells of elephants. This should ALWAYS be done by manual counting the different cell types on blood smears, stained with Wright-Giemsa. See also the Manual Differential WBC Count.
Estimating the platelet count is best done by calculating the average of platelets counts in 10 fields x 15,000, which gives the Estimated platelet count/µL.
See also: Manual platelet count (Cornell University).
The table below shows the normal hematology values for Asian and African elephants (Wiedner, E. 2015).
Perryn K.L. et al. 2020. Biological variation of hematology and biochemistry parameters for Asian elephant (Elephas maximus), and applicability of population-derived reference intervals. Journal of Zoo and Wildlife Medicine 51(3): 643–651
Weisbrod T.C., Isaza R., Cray C., Adler L., and Stacy N.I. 2021. The importance of manual white blood cell differential counts and platelet estimates in elephant hematology: blood film review is essential. Veterinary Quarterly, 41:1, 30-35, DOI: 10.1080/01652176.2020.1867329. (Click here for the complete text).
Wiedner E.. 2015. Proboscidea. In: Fowler's Zoo and Wild animal Medicine 8.
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