ISRAEL JOURNAL OF
VETERINARY MEDICINE
Vol. 56 (4) 2001
THE EFFECT OF SEASON ON THE BLOOD PROFILE
OF THE AFRICAN GIANT RAT (Cricetomys
gambianus, Waterhouse)
F. O. Olayemi1, O. A. Oke2, J. O. Oyewale1 and A. O. Ogunsanmi3
1. Department of Veterinary Physiology and Pharmacology 2 . Department of Veterinary Anatomy 3. Department of Wildlife and Fisheries - University of Ibadan, Ibadan, Nigeria.
Summary
The effect of seasonal variation on the haematological and plasma biochemical parameters
was determined in the adult wild African rat (Cricetomys gambianus, Waterhouse). It was
observed that during the dry season, the giant rat had higher values of mean corpuscular
volume, sodium, chloride, bicarbonate, calcium, creatinine, albumin, globulin and total protein
but lower values of haemoglobin concentration, mean corpuscular haemoglobin, mean
corpuscular haemoglobin concentration, total white blood cell count and urea than the same
animal during the wet season. However, there were no significant differences in the
erythrocyte count, packed cell volume, potassium and albumin/globulin ratio of the African
giant rat during the dry and wet seasons.
Introduction
The African giant rat (Cricetomys gambianus, Waterhouse) is a wild rodent with a body
weight ranging from 0.86-1.13 kg (1). It is found in different parts of Africa, where it serves as
supplementary protein diet for rural dwellers. There are few reports on their haematological
values. These includes a report on the effect of domestication on its blood picture (2,3); a
comparative study of the haemogram of the African giant rat and the Wistar rat (4); a detailed
study on its haematology and plasma biochemistry (1,5); a report on the haematological
changes during the oestrus cycle (6).
This report, a part of the ongoing studies, describes the effect of seasonal variation on the
haematological plasma biochemical parameters of the African giant rat in Nigeria.
Materials and Methods
Twelve apparently healthy adult wild African giant rats (Cricetomys gambianus,
Waterhouse) of both sexes were used in this study. Their age could not be determined as
they were captured from a bush in Ibadan, Nigeria. They were then transferred to the animal
house of the Faculty of Veterinary Medicine, University of Ibadan. Each rat was placed in a
separate cage in the animal house, which was adequately ventilated, with a similar
temperature and relative humidity to that of the environment (below).
The rats were fed on a diet of mouse cubes (21% protein, 3.5% fat, 6% fiber, 0.8% calcium,
0.8% phosphorus, Ladokum feeds, Ibadan, Nigeria). This was supplemented with palm kernel
fruits and they were given water ad libitum. The feed of the giant rat was similar in both the
dry and wet seasons, thereby limiting the variables to only the season while the other factors
such as feed, housing and management of the rats were kept constant. The giant rats were
acclimatized to their new environment for 28 days before the commencement of the study.
In September, during the wet season, each giant rat was anaesthetized using ether. Blood
was collected from the orbital sinus into a vessel containing ethylene diamine tetraacetic acid
(EDTA) (2mg/ml of blood). Red blood cell (RBC) and white blood cell (WBC) were counted
with a haemocytometer. Packed cell volume (PCV) was determined using the
microhaematocrit method. Haemoglobin (Hb) concentration was measured by
cyanmethaemoglobin method (7). Mean corpuscular volume (MCV), mean corpuscular
haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were
calculated from the values of RBC, PCV and Hb (7). The remaining blood samples were
centrifuged at 3000 g for 10 minutes to obtain plasma. Sodium and potassium concentrations
of plasma were determined by standard flame photometry, chloride by the method of Schales
and Schals (8), calcium and bicarbonate according to the method by Toro and Ackerman (9).
Total protein was determined using biuret method (10). Globulin was calculated by
subtracting albumin from total protein. Urea and creatinine were determined according to
Harrison (11).
The rats were bled and the blood analyzed again in February during the dry season, to
determine the effect of seasonal variation.
Data on the ambient temperature and relative humidity on the days of sampling were
obtained from the Department of Geography, University of Ibadan. The ambient temperature
and relative humidity of 260C and 82% respectively, were recorded for the wet season (22nd
September, 1997) and 280C and 78% respectively for the dry season (25th February, 1998).
The results obtained were statistically evaluated using Students’ t-test.
Results
Table 1 compares the mean values of RBC, total WBC, PCV, Hb, MCV, MCH and MCHC of
the rat during the dry and wet seasons. The rat had significantly higher Hb concentration
(p<0.001), MCHC (p<0.001), MCH (p<0.05) and total WBC count (p<0.05) but lower
(p<0.001) MCV in the dry than in the wet season. The values of RBC and PCV were similar in
both seasons.
Results of the plasma electrolyte, protein and metabolite concentrations during the wet and
dry seasons are presented in Table 2. The levels of Na, Cl, HCO3, Ca, creatinine, albumin
and globulin were significantly higher (p<0.001) but the level of urea was significantly lower
(p<0.001). Total protein concentration was significantly lower (p<0.001) during the dry
season. The values of potassium and albumin/globulin ration were similar in both seasons.
Table 1: Total leukocyte count and erythrocyte values (means±S.D.) of the adult African giant
rat during the dry and wet seasons.
Parameters
Dry season (n=12)
Wet season (n=12)
RBC (X106/µ)
5.50±1.25
6.19±1.58
PCV (%)
50.53±5.03
47.67±4.02
Hb (g/dl)
11.58±1.06
14.65±2.63*
MCV (fl)
96.45±28.88
80.64±17.52*
MCH (pg)
22.68±8.39
25.00±6.57**
MCHC (g/dl)
23.37±3.11
30.82±5.52*
WBC (X103/µ)
7.08±0.29
8.57±2.51**
Value significantly different from dry season at *p<0.001 and **p<0.05
Table 2: Plasma electrolyte, protein and metabolite levels (mean±S.D.) of the African giant rat
during the dry and wet seasons.
Parameters
Dry season (n=12)
Wet season (n=12)
Sodium (mmol/L)
171.83±10.56
98.52±8.52*
Potassium (mmol/L)
5.52±1.24
5.49±0.56
Chloride (mmol/L)
126.08±7.76
82.45±1.73*
Bicarbonate (mmol/L)
25.25±1.91
10.33±0.65*
Calcium (mg/dl)
11.50±0.91
2.65±0.50*
Total protein (g/dl)
7.35±0.94
5.82±0.34**
Albumin (g/dl)
3.50±0.57
2.67±0.32*
Globulin (g/dl)
3.86±0.52
3.17±0.25*
Albumin/globulin ratio
0.85±0.07
0.85±0.12
Urea (mg/dl)
5.14±1.27
11.92±2.43*
Creatinine (mg/dl)
2.10±0.58
0.60±0.10*
Value significantly different from dry season at *p<0.001 and **p<0.05
Discussion
the wet season. It may have been more appropriate for the sampling to be done for a longer
period of time in both seasons, unfortunately the African giant rat used for this study are wild
rodents and they were not easily captured. For this reason, few were sampled on a single day
during the dry and wet seasons. Similar methods of blood sampling, once in each season,
were used in determining the influence of season on the blood profile in some wild species of
waterfowl (12) and White Fulani cattle (13).
The Hb concentration, MCH and MCHC were significantly higher in the African giant rat in
wet than in the dry season (Table 1). This is in agreement with the observation of Saror and
Coles (13) in which White Fulani cattle were also reported to have higher Hb, MCH and
MCHC values during the wet season. The higher Hb, MCH and MCHC during the wet season
in the present study may be due to lower water intake during the wet season than during the
dry season, which is as a result of lower ambient temperature and higher relative humidity of
260C and 82% respectively during the wet season compared with the higher ambient
temperature of 280C and a lower relative humidity of 78% during the dry season. This may have
resulted in changes in water content of the blood and blood viscosity as the total body water decreased
with a decrease in water intake. The lower water intake during the wet season would lead to
haemoconcentration, which resulted in the relative higher Hb, MCH and MCHC.
The total WBC count was significantly lower in the giant rat during the dry season (Table 1).
Similarly, Saror and Coles (13) reported a higher total WBC values in White Fulani cattle
during wet seasons. Also, during the dry season Oyewale and Olowookorum (14) reported a
total WBC count of 12.18x103/µl in the West African dwarf goat, which was lower than the
values of 16.14x103/µl reported by Oduye (15) for this breed during the wet season. The observation
in the African giant rat of the present study may be due to higher levels of subclinical parasitic
infection during the wet season.
In the present study the plasma levels of Na, Cl, HCO 3 and Ca in the African giant rat were
significantly lower during the wet than during the dry season (Table 2). The low plasma electrolyte
levels observed during the wet season in this study were however similar to values of 96.85mmol/L
(sodium), 5.47mmol/L (potassium), 81.14mmol/L (chloride), 10.43mmol/L (bicarbonate) and
2.72mg/dl (calcium) obtained for the adult African giant rat during the wet season (5). In the present
study, it is however surprising how the giant rat could cope with such low levels of plasma electrolyte
in the wet season, for example the level of plasma bicarbonate was 10.33mmol/L and the animal did
not show any sign of acidosis such as hyperpnea. Also the value of plasma calcium, which was
2.65mg/dl in the wet season, is rather low. It seems the giant rat have evolved adaptive measures to
cope with the variation in the plasma electrolyte with the dry and wet seasons. However since similar
diet was given to the giant rat during the dry and wet seasons, further study seems necessary to
determine if there is an increase in the utilization of the plasma electrolyte during the wet season.
In the present study the total protein, albumin and globulin concentrations were higher in
the African giant rat during dry than during the wet season, since the ambient temperatures
was higher and relative humidity was lower during the dry season, than during the wet
season, it may be that the giant rats were dehydrated during the dry season which may have
elevated the concentration of the plasma proteins (16). Saror and Coles (13) did not observe
any seasonal variation in the total plasma protein, albumin and globulin of the White Fulani
cattle. Akerejola (17) however, reported higher values of total proteins and albumin in the
White Fulani cattle during the wet season.
The plasma urea in the African grant rat was higher in the wet season (Table 2). This
finding is similar to observation made in the White Fulani cattle (13,17), African elephant (18)
and African white bellied pangolin (19), in which they all have higher values of plasma urea
during the wet season. Howe (20) reported that the high level of serum urea in the Zebu cattle
was due to the efficient digestion of dietary protein. It is therefore likely that the higher plasma
urea level in the African giant rat during the wet season is as a result of a more efficient
digestion of dietary protein.
References
1. Oyewale, J.O. Olayemi, F.O. and Oke, O.A.: Haematology of the wild adult African grant rat
(Cricetomys gambianus, Waterhouse). Veterinarski arhiv, 68: 91-99; 1998.
2. Olowookorun, M.O: Studies on the influence of domestication on the blood picture of the
African grant rat. Preliminary observation. Nig. J. Forest. 4: 73-74, 1974.
3. Olowookorun, M.O: Some aspects of the physiology of the domesticated African giant rat. In:
Ajayi, S.S. and Halstead, L.B. (Eds): Wildlife management in Savannah woodland. Taylor and
Francis Limited. London pp. 142-150, 1979.
4. Durotoye, L.A. and Oke, B: A comparative study of the haemogram of the African giant rat
(Cricetomys gambianus, Waterhouse) and the Wistar rat. Trop. Vet. 8: 29-38, 1990.
5. Oyewale, J.O, Oke, O.A., Olayemi, F. O. and Ogunsanm, A.O.: Electrolyte, enzyme, protein
and metabolite levels in the blood. Plasma of the wild adult African giant rat (Cricetomys
gambianus, Waterhouse). Veterinarski arhiv 68: 127-133,1998.
6. Oke O.A., Oke, B. O. and Olayemi F.O. Haematological changes during the oestrous cycle of
the African grant rat (Cricetomys gambianus, Waterhouse). Trop.Vet. 18: 202-206, 2000.
7. Schalm, O.W., Jain, N.C and Carroll, E.J.: Veterinary Haematology 4th ed. Lea and Febiger
Philadelphia, 1975.
8. Schales, P. and Schales, S.S.: A simple and accurate method for the determination of
chloride in biological fluids J. Chem.140: 879-884, 1941.
9. Toro, G. and Ackerman, P.: Practical Clinical Chemistry, 1st ed. Little Brown and company,
Boston, 1975.
10. Reinhold, J.G.: Standard Method of Clinical Chemistry 1st ed. (Reiner, M., ed.) Academic
Press. New York. pp. 88, 1953.
11. Harrison, G.A.: Chemical methods in Clinical Medicine 3rd ed. Churchill, London, 1947.
12. Shave, H.J. and Howard, V. A.: hematologic survey of captive waterfowl. J. Wildl. Dis, 12:
195-201, 1976.
13. Saror, D. and Coles, E.H.: The blood picture of White Fulani (Zebu) and White
Fulani/Fresian (crossbreed) dairy cow. Bull. Epizoot Dis. Afr. 21: 485-487, 1973.
14. Oyewale, J.O and Olowokorun, M.O.: Diurnal variation in the haematological values of West
African dwarf goat. Bull. Anim. Hlth Prod. Afr. 34: 161-164,1986.
15. Oduye, O.O.: Haematological values of goats and sheep. Trop. Anim. Hlth Prod.8: 131-136,
1976.
16. Finco, D.R.: Kidney Function In: J.J. Kaneko (ed.): Clinical Biochemistry of Domestic Animals.
4th ed. Academic press, Toronto, 1989.
17. Akerejola, O.O., Umuna, N.N. and Denis S.M.: Serum biochemical levels of cattle in Northern
Nigeria. Nig. Vet. J. 9: 26-31, 1980.
18. Brown, I.R.F., White, P.T. and Malpas, R.C.: Proteins and other nitrogenous constituents of
the blood serum of the African elephant (Loxodonta africana). Comp. Biochem. Physiol. 59A:
267-270, 1978.
19. Oyewale, J.O., Ogunsanmi, A. and Ozegbe, P.C.: Haematology of the adult African whitebellied pangolin (Manis tricuspis) Veterinarski arhiv 67: 261-266, 1997.
20. Howes, Y.R., Hentges, Jr, J.F. and Davis, G.K.: Comparative digestive powers of Hereford
and Brahman cattle. J. Anim. Sci. 22: 22 1963.