Hematology in rabbits and guinea pigs
Popularity of rabbits and guinea pigs as pets is constantly rising. Consequently these animals are more often seen as patients in our vet clinics. Quite often diagnostic work in these species is a challenge in small animal practice. Hematology and clinical chemistry as well as serology can provide helpful information. While we find lots of data concerning lab parameters for laboratory animals - even with reference to different breeds, age groups or sexes – only little information is available on reference values for rabbits and guinea pigs kept in family homes. This issue of our lab information deals with hematology of rabbits and guinea pigs kept at homes, giving information on reference values as well as on special findings.
| Taking a blood sample|
The total blood volume of a rabbit equals 4,5-8,1 % of the body mass (55-66 ml/kg body mass). In healthy animals 6-10 % of the blood volume (3,5-6,5 ml/kg KM) can be drawn for analysis (Bivin und Timmons, 1974; Murray, 2000).
In guinea pigs we find similar conditions, 4,5-8,3 % of the body mass being blood (69-75 ml/kg body mass). In healthy animals 7-10 % of the total blood vollume can be drawn (0,5-0,7 ml/100g body mass) for analysis (Anderson, 1987; Quesenberry et al., 2004).
Both, rabbits as well as guinea pigs are very susceptible to stress. Stress resp. excitement during or right before sampling procedure will result in changes of various laboratory parameters. This phenomenon is well known in other mammals as well. Therefore it is wise to have as little manipulation as possible prior to taking a blood sample. Restraining should be performed with minimal force, covering the head with a cloth e.g. can be helpful to minimize the stress. For blood sampling in practice commonly the vena saphena is used in both, rabbits and guinea pigs.
Since the volume that can be collected is usually limited in rabbits and guineas pigs preferably heparinized samples are collected for both hematology and clinical chemistry. The use of heparinized samples is possible for hematology as well as most parameters in clinical chemistry and serology. It is wise to prepare a smear in practice without any delay to preserve the cell morphology for microscopical examination. Even when no exact cell count can be performed due to transport problems or clotting events at least a differential and an estimation of cell numbers is possible that way. Just working with a smear thus can be a compromise in case of scarce volume or clotting or any other event hampering the routine analysis. Optimum information of course can only be obtained when a correctly collected sample is available.
Hematologic parameters in rabbits
During the first days post partum the granulocytic hemogram of the rabbits changes into a lymphocytic one and then stays that way. Since neutrophilic granulocytes show an acidophilic staining these cells are often refered to as pseodueosinophilic ones. Indeed on first sight there is a threat of misinterpreting the neutrophils as eosinophils. Eosinophilic granulocytes are clearly larger though and show larger and more distinct granules in constrast to pseudoeosinophils (Hein und Hartmann, 2003; Walberg und Loar, 2004).
In case of acute bacterial infections rabbits react rather infrequently with leucocytosis (Hillyer, 1994). Typically we find changes towards a granulocytic picture though. As a rule of thumb, when 80-60% of the cells in the differential are identified as pseudoeosinophils an inflammatory process is most likely. Stress induced changes have to be carefully considered as well. Animals exposed to stress will show an elevated blood pressure due to release of ACTH and adrenalin. Consequently the marginal pool of pseudoeosinophils is lowered and the central pool gains these pseudoeosinophils. This results in a relative rise of pseudoeosinophils within the venous blood lacking any signs of left shift and accompanied by a relatively lowered number of lymphocytes (Harkness, 1987). Bands as pseudoeosinophils are observed very rarely. A critical interpretation taking into account the individual anamnesis is therefore extremely important.
In contrast to dogs and cats, rabbits do not show signs of eosinophilia due to parasites or to hypersensitivity (Fudge, 2000). The only cause of eosinophilia reported is according to Hein due to infestation with mites in guinea pigs. Leucemia is observed in rabbits as well as in guinea pigs - in these cases maturation of leucocytes in the bone marrow is abnormal and leucocytosis in the peripheral blood can be observed.
Blood smear of a rabbit with 2 lymphocytes
Hein and Hartmann (2003) published reference values for rabbits kept in family homes as a result of hematologic investigations:
Hematologic reference values for rabbits
Reference value rabbit
111-156 g/l (>4 mo.)
118-156 g/l (1,5-4 mo.)
0-5 % (> 4 mo.)
0-0,5 G/l (> 4 mo.)
0-0,7 % (1,5-4 mo.)
Blood smear of a rabbit with pseudoeosinophil (note the fine granulation of the cytoplasma)
Blood smear of a rabbit with 2 monocytes
|Hematologic parameters in guinea pigs |
In contrast to erythrocytes in various other species the ones of guinea pigs are comparatively larger in size and lower in number (Constable, 1963). As seen in rabbits, guinea pigs also have a lymphocytic hemogram and in guinea pigs as well stress can cause a considerable leucocytosis. In this species neutrophils are stained acurophilic. As well as in rabbits these are named pseudoeosinophils. These cells can be differentiated from eospinophils by color and morphology of the cytoplasmatic granula like in rabbits (Walberg and Loar, 2004).
Blood smear of a guinea pig
A peculiarity in blood smears of guinea pigs are the so called Kurloff cells or Foa Kurloff cells. These cells are mononuclear cells with inclusion bodies. Large inclusion bodies always appear singular in the cytoplasma. Due to their size the nucleus can be dislocated towards the periphery with a shape resembling a reaping hook. Frequency of these cells with inclusion bodies can be up to 3-4 % of the leucocytes. Kurloff cells are rarely seen in young animals and in males. In females Kurloff cells are observed more often and the amount correlates with the estrogen level (Percy und Barthold, 2001). Presumably these cells are an equivalent to natural killer cells of other mammals.
Kurloff cells in a blood smear of a guinea pig.
asterisk: inclusion body
Reference values for guinea pigs (Hein and Hartmann 2003)
Reference value guinea pig
0-15 % (> 4 mo.)
0-4 % (1,5-4 mo.)
0-1,6 G/l (> 4 mo.)
0-2,7 G/l (1,5-4 mo.)
| Note: |
|1. || ||Due to small volumes of blood accessible heparinised samples are preferred|
|2. || ||Preparation of blood smears in pratice are recommended to overcome problems (e.g. morphologic changes) that might occur due to transport. |
|3. || ||Rabbits and guinea pigs both show lymphocytic hemograms. |
|4.|| ||Neutrophils are named pseudoeosinophils due to their characteristic staining with azurophilic granules. |
|5.|| ||Both stress induced as well as due to inflammation a change to relative pseudoeosinophilia and lymphopenia is observed. Careful interpretation is needed. Leucocytosis is rarely seen. |
|6.|| ||In case of leucocytosis leucemia has to be ruled out carefully- most possibly cause of elevated numbers of white blood cells. |
|7.|| ||Recommendations for possible sampling volume: |
Rabbit - 3,5-6,5 ml/kg body mass
Guinea pig - 0,5-0,7 ml/100g body mass