VETERINARSKI ARHIV 68 (2), 91-99, 1998

ISSN 0372-5480
Printed in Croatia

Haematology of the wild adult African giant rat (Cricetomys gambianus, Waterhouse)

Johnson O. Oyewale¹*, Funsho O. Olayemi¹, and Olusola A. Oke²

¹Department of Veterinary Physiology and Pharmacology, University of Ibadan, Ibadan, Nigeria

²Department of Veterinary Anatomy, University of Ibadan, Ibadan, Nigeria

* Contact address:
Dr. Johnson O. Oyewale,
Department of Veterinary Pharysiology and Phmacology, University of Ibadan, Ibadan, Nigeria,
Phone: 234 2 81 03 168; Fax: 234 2 81 03 118; E-mail: library@kdl.ui.edu.ng

OYEWALE, J. O., F. O. OLAYEMI, O. A. OKE: Haematology of the wild adult African giant rat (Cricetomys gambianus, Waterhouse). Vet. arhiv 68, 91-99, 1998.

ABSTRACT

Haematological data were determined in apparently healthy wild adult male and female African giant rats (Cricetomys gambianus, Waterhouse). Significant sex differences were not found in the red blood cell count, packed cell volume, haemoglobin concentration and erythrocyte indices. However, erythrocyte osmotic fragility was significantly higher and the total white blood cell count was significantly lower in the female than in the male. The differential white blood cell counts did not differ significantly between sexes. The haematological data obtained from African giant rats are compared with the values reported in the same tropical environment in humans and laboratory and domestic animals.

Key words: haematology, wild, adult, African giant rat, Cricetomys gambianus

Introduction

There are abundant data in the literature on haematological parameters of a variety of species. In mammals, these values are most numerous for domestic species. They are less numerous for many captive or free-ranging species. Studies on free-ranging species are typically limited to a small number of blood parameters. There have been very few haematological studies on wild and captive African giant rats (Cricetomys gambianus, Waterhouse). The reports of OLOWOOKORUN (1974, 1979) were limited to erythrocyte and leucocyte counts and packed cell volume and haemoglobin concentration in 3 wild and 9 laboratory-bred adult male giant rats. DUROTOYE and OKE (1990) have also reported some haematological values in 17 male giant rats. However, none of these previous studies has attempted to assess the possible effect of sex. The African giant rat serves as a ready source of supplementary dietary protein for the local people in certain parts of Africa. The present study was undertaken to determine the haematological values in adult male and female African giant rats to establish normal values and the differences between the sexes.

Materials and methods

Adult male and female African giant rats (Cricetomys gambianus, Waterhouse) were captured from the wild near Ibadan, Nigeria and kept in the animal house of the Faculty of Veterinary Medicine, University of Ibadan, Nigeria. They were fed on a diet of mouse cubes (21% protein; 3.5% fat; 6% fibre; 0.8% calcium; 0.8% phosphorus; Ladokun Feeds Limited, Ibadan, Nigeria) and were given water ad libitum. Feeding was supplemented with palm kernel fruits.

Two weeks after capture, apparently healthy 5 males and 10 female giant rats were used for this study. Each animal was weighed and anaesthetised using ether. Blood was collected from the orbital sinus into a bottle containing ethylene diamine tetraacetic acid (EDTA) (2 mg/ml of blood).

Red blood cells (RBC) and white blood cells (WBC) were counted with haemocytometers. Packed cell volume (PCV) was determined using the microhaematocrit method. Haemoglobin (Hb) concentration was measured by the cyanmethaemoglobin method. From the above data, the mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were calculated (SCHALM et al., 1975). Osmotic fragility of erythrocytes was determined as described previously (OYEWALE, 1992) using l% phosphate-buffered sodium chloride (NaCl) solution of pH 7.7 at 29 °C, except for the NaCl concentrations (0.0 - 0.7%) used (see Figs. 1 and 2). The percentage of haemolysis in each concentration of NaCl was evaluated using haemolysis in distilled water (0% NaCl) as l00%. Blood smears were stained with Giemsa stain for differential WBC counts.

All data were analysed statistically using Student's t-test.

Results

The mean values for body weights and RBC, PCV, Hb, MCV, MCH and MCHC in male and female giant rats are shown in Table 1. The body mass was significantly greater in the male than in the female. However, none of the erythrocyte parameters was significantly different between sexes. Table 2 shows a comparison of the erythrocyte parameters in the giant rat with the values reported in the same tropical environment in the wild pangolin (Manis tricuspis) (OYEWALE et al., 1997). Also included in Table 2 for comparison are the erythrocyte values obtained in the same environment in humans (EZEILO and OBI, 1983) and in domesticated mammals such as White Fulani cattle (ODUYE and OKUNAIYA, 1971), West African Dwarf sheep (ODUYE, 1976) and Nigerian goats (ODUYE, 1976) and laboratory rats (OYEWALE, 1987). The RBC count for giant rats was similar to that in humans. However, giant rats had a significantly higher RBC count than pangolins (P<0.01 ) and a significantly lower count than laboratory rats (P<0.05), cattle (P<0.01), sheep (P<0.001) and goats (P<0.001). Thc PCV in giant rats was significantly higher (P<0.001) than in pangolins, laboratory rats, cattle, sheep and goats, but was similar to that in humans. Although the Hb concentration in giant rats was not significantly different from the values in laboratory rats and humans, it was significantly higher (P<0.001) than in pangolins, cattle, sheep and goats. The MCV value for giant rats was close to the values reported in pangolins and humans, but was significantly higher (P<0.001) than those found in laboratory rats, cattle, sheep and goats. The MCV value for giant rats was also significantly higher than in laboratory rats (P<0.001), but agreed with the values in humans and pangolins. However, the MCHC value in giant rats, which was similar to the values in humans and sheep, was significantly lower than in laboratory rats (P<0.001) and goats (P<0.05) and significantly higher than in pangolins (P<0.01).

Table 1. Mean (± SD) body mass and erythrocyte values in male and female African giant rats

Table 2. Comparison of erythrocyte values (mean±SD) in African giant rats, pangolins, laboratory rats, humans, cattle, sheep and goats in the same tropical enviroment

ND=Not determined

As shown in Fig. 1, except at 0.7% NaCl, where the osmotic fragility of erythrocytes in female giant rats was significantly greater (P<0.05) than in males, no significant sex difference appeared in the fragility values at the various NaCl concentrations used. Fig. 2 compares the osmotic fragility of giant rat erythrocytes with the values reported in the same tropical environment in other mammals such as rabbit, mouse, goat, sheep, pig and cattle (OYEWALE, 1993). The fragility of giant rat erythrocytes was significantly less (P<0.001) than that of rabbit erythrocytes at NaCl concentrations of 0.5%, 0.4% and 0.3%. The giant rat erythrocyte was also significantly less fragile than the mouse erythrocyte at NaCl concentrations of 0.6% (P<0.05) and 0.4% (P<0.001). Goat erythrocytes showed significantly greater (P<0.001) osmotic fragility than giant rat erythrocytes at NaCl concentrations of 0.7%, 0.6%, 0.5%, 0.4% and 0.3%. Also, sheep erythrocytes appeared significantly more fragile than giant rat erythrocytes at NaCl concentrations of 0.7% (P<0.001), 0.6% (P<0.001), 0.5% (P<0.001), 0.4% (P<0.001) and. 0.3% (P<0.01). Giant rat erythrocytes were significantly less osmotically fragile (P<0.001) than pig or cattle erythrocytes at NaCl concentrations of 0.6%, 0.5%, 0.4% and 0.3%.

Fig. 1. Osmotic fragility of erythrocytes of 5 male and 10 female giant rats. Each point is the mean ± SD.

Fig. 2. Osmotic fragility of erythrocytes of 15 giant rats (present study) and 7 rabbits, 6 mice, 10 pigs, 22 cattle, 11 goats and 12 sheep (OYEWALE, 1993). Each point is the mean ± SD.

Table 3 presents the total and differential WBC values in the male and female giant rats. The total WBC count was significantly higher (P<0.05) in males than in females. However, the differential WBC values did not differ significantly between sexes in giant rats. Table 4 shows a comparison of the WBC values in giant rats with those in humans (EZEILO and OBI, 1983), pangolins (OYEWALE et al., 1997), White Fulani cattle (ODUYE and OKUNAIYA, 1971), West African dwarf sheep (ODUYE, 1976) and Nigerian goats (ODUYE, 1976) in the same environment. The total WBC count in giant rats was similar to that found in this environment in humans, but significantly lower (P<0.001) than in cattle, sheep and goats, and significantly higher (P<0.01) than in pangolins. The lymphocyte count in giant rats was significantly higher (P<0.001) than in humans and pangolins. Although the percentage of lymphocytes in giant rat blood was similar to that in cattle blood, it was significantly higher (P<0.001) than that in pangolin, sheep or goat blood. The neutrophil count in giant rats was similar to that in pangolins, but significantly lower (P<0.05) than that in humans. The percentage of neutrophils in the blood of giant rats was also close to that in cattle, although significantly lower (P<0.001) than in pangolins, sheep and goats. The eosinophil count in giant rats was significantly higher (P<0.01) than in pangolins, but significantly lower (P<0.001) than in humans. The percentage of eosinophils in giant rat blood was significantly higher (P<0.01) than in pangolin blood, while it was significantly lower than the percentages in cattle (P<0.001), goat (P<0.01) and sheep blood (P<0.001). The giant rat blood had a significantly higher (P<0.001) number and a significantly higher (P<0.001) percentage of basophils than pangolin blood. The monocyte count in giant rats was significantly higher (P<0.001) than in humans and pangolins. The percentage of monocytes in the blood of giant rats was similar to that in cattle blood, but significantly higher than the percentages in pangolin (P<0.05), sheep (P<0.001) and goat blood (P<0.001).

Table 3. Mean (±SD) leucocyte values in male and female African giant rats

*=Value expressed as a percentage of total WBC count

Table 4. Comparison of leucocyte values (mean±SD) in African giant rats, pangolins, humans, cattle, sheep and goats in the same tropical enviroment

Values in breckets expressed as percentage of total WBC count; ND=Not determined

Discussion

The erythrocyte count has been observed to be higher in males than in females in cats (LEWIS, 1941) and goats (HOLMAN and DEW, 1966). However, in mink (Mustela vison) (WEISS et al., 1994), pangolins (Manis tricuspis) (OYEWALE et al., 1997), donkeys (NAYERI, 1978), sheep (ODUYE, 1976) and horses (SCHALM et al., 1975), no significant sex difference was found. This agrees with our finding in giant rats.

Male donkeys have a greater Hb concentration than females, according to NAYERI (1978). Higher values have also been reported in male horses (SCHALM et al., 1975) and cats (LEWIS, 1941). However, ODUYE and OKUNAIYA (1971) found lower Hb values in male than in female cattle. In the present study with giant rats, in agreement with the observations in mink (WEISS et al., 1994), sheep (ODUYE, 1976) and pangolins (OYEWALE et al., 1997), the Hb concentration was not significantly different between sexes.

The mean PCV, Hb and RBC values of the wild giant rats obtained here are within the ranges found in humans and domestic animals in the same environment. For example, as can be seen in Table 2, the mean PCV value in giant rats is similar to that in humans (EZEILO and OBI, 1983), but lower than the values reported in laboratory rats (OYEWALE, 1987), cattle (ODUYE and OKUNAIYA, 1971) and sheep and goats (ODUYE, 1976). The Hb concentration in giant rats agrees with those reported in humans (EZEILO and OBI, 1983) and laboratory rats (OYEWALE, 1987), even though it is higher than the values in cattle (ODUYE and OKUNAIYA, 1971) and sheep (ODUYE, 1976). The RBC count is lower in giant rats than in cattle (ODUYE and OKUNAIYA, 1971 ) and goats (ODUYE, 1976), but is similar to the value in humans (EZEILO and OBI, 1983).

The value of MCV in giant rats was higher, as in pangolins (OYEWALE et al., 1997), than the data in laboratory rats, cattle, sheep and goats (Table 2). This could be due to the lower number of circulating erythrocytes in giant rats, as in pangolins (OYEWALE et al., 1997), than in these laboratory and domestic animals (Table 2). The MCHC value in giant rats, however, agrees with those of sheep (ODUYE, 1976) and humans (EZEILO and OBI, 1983).

Our observation that the osmotic fragility of erythrocytes was greater in females than in male giant rats disagrees with the findings in humans (GODAL et al., 1980), ducks (OYEWALE and AJIBADE, 1990) and guinea-fowls (OYEWALE, 1988), where no sex difference was observed, and in domestic fowls (MARCH et al., 1966), in which males showed greater fragility than females. It has been shown that in domestic fowls (MARCH et al., 1966), oestrogen decreases erythrocyte fragility by increasing the fatty acid composition of the erythrocyte membrane, while testosterone has no effect on erythrocyte osmotic fragility. Whether our present finding is unrelated to the actions of these hormones, or whether their effects are different on giant rat erythrocytes, has yet to be determined. The lower osmotic fragility of giant rat erythrocytes than rabbit, mouse, goat, sheep, cattle or pig erythrocytes (Fig. 2) could, as suggested by OYEWALE (1993), have been due to factors that vary between species, such as the nature of the erythrocyte membrane or the physical and chemical constitution of the cell.

In horses, the female has a slightly higher mean total WßC count than the male (SCHALM et al., 1975). A higher mean total WBC count in the male as against the female was reported in donkeys (NAYERI, 1978) and goats (SCHALM et al., 1975), although the difference was not significant. The present study in giant rats showed that males had significantly higher mean total WBC count than females because they had slightly more lymphocytes, neutrophils and eosinophils (Table 3). The mean total WBC count in giant rats was similar to the count in humans (EZEILO and OBI, 1983), but higher than that reported in pangolins (OYEWALE et a1., 1997) and lower than the values found in cattle (ODUYE and OKUNAIYA, 1971) and sheep and goats (ODUYE, 1976).

Our results show that the neutrophil count is much lower than the lymphocyte in giant rats. This agrees with similar observations in humans (EZEILO and OBI, 1983), donkeys (NAYERI, 1978) and cattle, pigs, sheep and goats (SCHALM et al., 1975). However, it disagrees with the findings in horses (HANSEN and TODD, 1951) and dogs and cats (SCHALM et al., 1975), where neutrophil counts are much higher than lymphocyte.

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Received: 27 January 1998
Accepted: 11 March 1998

OYEWALE, J. O., F. O. OLAYEMI, O. A. OKE: Hematoloski nalazi u odraslog divljeg africkog divovskog stakora (Cricetomys gambianus, Waterhouse). Vet. arhiv 68, 91-99, 1998.

SAZETAK

Odredene su hematoloske vrijednosti u zdravih, odraslih muzjaka i zenki divljeg africkog divovskog stakora (Cricetomys gambianus, Waterhouse). Nisu ustanovljene znacajne razlike medu spolovima u broju crvenih krvnih stanica, ukupnom stanicnom volumenu, koncentraciji hemoglobina i sadrzaju eritrocita. Medutim, osmotska osjetljivost eritrocita bila je znacajno veca, a ukupan broj bijelih krvnih stanica znacajno manji u zenki nego u muzjaka. Diferencijalna bijela krvna slika nije se znacajno razlikovala medu spolovima. Dobivene hematoloske vrijednosti u africkog divovskog stakora usporedene su s vrijednostima u covjeka, laboratorijskih i domacih zivotinja iz istog tropskog podneblja.

Kljucne rijeci: hematologija, divlji, africki divovski stakor, Cricetomys gambianus