Abstract: Total Platelet count (PLT), Mean Platelet Volume (MPV), Plateletcrit (PCT) and Platelet Distribution Width (PDW) were determined, along with hematological parameters, in blood samples from 8 captive mountain gazelles (Gazella gazella). The mean values of PLT, PCT, MPV and PDW were: 288.75±168.8 (x10³ μL^-1), 0.20±0.13%, 7.24±0.84 (fl) and 34.84±2.36%, respectively. The corresponding values for parallel red cell variables were 13.48±1.17 (10¹² L^-1) for Red Blood Cell count (RBC), 52.70±5.45 (fl) for Hematocrit (HCT), 39.00±1.07 for Mean Corpuscular Volume (MCV) and 19.86+0.32% for Red cell Distribution Width (RDW). Correlation analysis revealed highly significant correlations for PCT with PLT (p<0.0001), PCT with HCT (p<0.001) and PDW with MCV (p<0.001). This study is the first record of platelet counts and platelet indices in mountain gazelles.

INTRODUCTION

Hematological reference values have been reported for different species of the genus Gazella including Grant's gazelle, Gazella granti (Drevemo et al., 1974; Seal and Schobert, 1976; Sleeman and Widdowson, 1993), Dorcas gazelle, Gazella dorcas (Bush et al., 1981; Pienado et al., 1990), cuvieri gazelle, Gazella cuvieri (Casado et al., 1991; Abaigar, 1993), dama gazelle, Gazella dama (Casado et al., 1991; Abaigar, 1993), mountain gazelle, Gazella gazella (Rietkerk et al., 1994), Thomson's gazelle Gazella thomsonii (Slessman and Widdowson, 1993), goitered gazelle Gazella subgutturosa (Yaralioglu et al., 2008) and Speke's gazelle, Gazella spekei (Travis and Eby, 2006).

However, very sparse information is found on platelet counts in gazelles (Yaralioglu et al., 2008; Travis and Eby, 2006), while no information exists on platelet indices in any of these species, nor indeed in any wild ungulate. Several platelet indices are known including Mean Platelet Volume (MPV), Plateletcrit (PCT), Platelet Distribution Width (PDW), Mean Platelet Component (MPC) and Platelet-Large Cell Ratio (P-LCR). The physiological, diagnostic and prognostic relevance of these relatively new indices is becoming increasingly recognized in human (Wiwanitkit, 2004; Kaito et al., 2005) and veterinary (Segura et al., 2007; Yilmaz et al., 2008) medicine. Hence, they are being determined as part of routine blood counts in many laboratories (Harold et al., 2008). The most important of these indices are the MPV, PCT and PDW (Wiwanitkit, 2004), which serve as markers of platelet size, function and reactivity and can therefore, be useful additional measurements in the diagnosis, differentiation and follow up of platelet-related disorders in man and animals (Bath and Butterworth, 1996; Amin et al., 2004; Kim et al., 2007; Harold et al., 2008; Nalbant et al., 2008). The following study was undertaken to provide preliminary information on the normal Platelet counts (PLT), MPV, PCT and PDW in captive mountain gazelles. Correlations between these indices and corresponding hematological variables are also provided.

MATERIALS AND METHODS

Eight adult, Arabian mountain gazelles (Gazella gazella) aged 3-5 years and weighing 18-20 kg were investigated. The animals comprised 5 non-pregnant females and 3 males, born and kept in captivity at King Khalid Wildlife Research Center near Riyadh, Saudi Arabia. They were fed on a ration of dried lucerne and commercial concentrate (crude protein 16%), with free access to water, routinely vaccinated against infectious diseases and given coccidiostats and anthelminthic drenches as necessary. All the gazelles were clinically normal at the time of sampling. About 10 mL blood samples were collected from each gazelle by jugular venipuncture into clean vacuotainer tubes (Becton, Dickinson and Co., USA) containing EDTA-K₂, while the animal was manually restrained. Each tube was inverted 2-3 times to ensure thorough mixing and analyzed within 2 h in the laboratory using an automated hematology analyzer (VetScan HM2; Abaxis Veterinary Diagnostics). Each sample was analyzed for PLT, PCT, MPV and PDW, as well as RBC, Hematocrit (HCT), Hemoglobin (Hb), Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH) and Mean Corpuscular Hemoglobin Concentration (MCHC).

The data were statistically analyzed using SAS 8.1 program for Windows. The Shapiro-Wilk normality test was used to check all parameters and most of the parameters were distributed normality. Therefore, Pearson correlations were used in the analysis of correlations between PLT, PCT, MPV and PDW and parallel red cell indices, namely RBC, HCT, MCV and RDW (Schork and Remington, 2000).

RESULTS AND DISCUSSION

Means, standard deviations, variance and 95% ranges of excepted values for the platelet and red cell parameters are presented in Table 1. There were no obvious discrepancies between these parameters in male and female gazelles and the data for both sexes are therefore combined. None of the platelet variables was previously known in the mountain gazelle and with the exception of the Platelets number (PLT), none of these variables was reported in other species of gazelle. The mean PLT in the mountain gazelle was ~290 (x10³ μL^-1), which compares well to that reported in goitered (Yaralioglu et al., 2008) and Speke’s gazelles (Travis and Eby, 2006) as well as humans (Kim et al., 1986) but is lower than that reported in cattle, sheep and goats and higher than that in equines (Jain, 1993). In common with these various species, however, the PLT of the mountain gazelle exhibited a wide range of variation (117-601 x10³ μL^-1). The MPV also appears to vary with species. While, the mean value presently recorded in the mountain gazelle (7.2±0.83fl) was lower than that recorded in humans (Wiwanitkit, 2004), it exceeded that reported in cattle, sheep, goats and equines (Watson and Authi, 1996) as well as camels (unpublished data). On the other hand, the PCT in the mountain gazelle averaged 0.2%, which is higher than that reported in sheep (Abdelhamid et al., 2007) but less than half of that reported in cattle (Yilmaz and Yesilbag, 2008) and only slightly lower than humans (Tohgi et al., 1991). By contrast, the PDW in the mountain gazelle, averaging ~35%, was twice as high as that reported in bovines (Yilmaz and Yesilbag, 2008). The corresponding mean value of PDW in normal adult humans was variably given as 15.66±0.52% by Kim et al. (1986) and 46.79±2.7% by Wiwanitkit (2004).

The mean Hb, MCV, MCH and MCHC values in the mountain gazelles were comparable to while, the mean RBC and HCT values were higher than, those previously reported in this species (Rietkerk et al., 1994). The present values also fell within the normal ranges for Dorcas, Grant's and Thomson's gazelles reviewed by Bush et al. (1981). Mean Hb, PCV, MCH and MCHC values in the mountain gazelles were also comparable with those reported in goitered gazelles (Yaralioglu et al., 2008), while RBC was lower and MCV higher in the latter species compared to the mountain gazelle. The RDW is a measure of variability of red blood cell size and its value may change in various clinical conditions associated with abnormalities in red cell production. As shown in Table 1, normal RDW in mountain gazelles averaged ~20% (19.4-20.5%). This value is somewhat higher than that reported in humans (Wiwanitkit, 2004) cattle (Yilmaz et al., 2008), sheep (Abdelhamid et al., 2007) and equines (Thrall et al., 2004).

Correlations between PLT, MPV, PCT and PWD and between these indices and their parallel red cell parameters in the mountain gazelles are presented in Table 2 and 3, respectively. Significant correlations were recorded for PCT with PLT (p<0.0001), PCT with MCV (p<0.005) and PLT with MCV (p<0.005), while no significant correlations were found between PCT and HCT and between MPV and MCV. These findings agree with those reported in humans (Wiwanitkit, 2004).

The latter author suggested that the absence of significant correlations between PCT and HCT and between MPV and MCV indicated that the sizes of red blood cells and blood platelets were independent of each other. On the other hand, in contrast to humans (Wiwanitkit, 2004) there was no significant correlation between PWD and RWD in the mountain gazelles. Also, no significant correlation between PLT and RBC was found in the present animals, suggesting that the numbers of red cells and platelets may also be independent of each other.

Table 1:	Descriptive statistics of platelet indices and hematological parameters in mountain Gazelle

Table 2:	Correlation coefficients between platelet indices in mountain Gazelles
***p<0.0001

Table 3:	Correlation coefficients between platelet indices and parallel red blood cell indices in mountain Gazelles
**p<0.005

The present study provides hitherto unknown data on the platelet indices in mountain gazelles. Further studies should be undertaken to investigate these variables in more detail, including their clinical significance in gazelles.

CONCLUSION

The number of platelets in the Arabian mountain gazelle (Gazella gazella) ranges between 147.6-430 x10³ μL^-1 (mean 288.75±168.8 x10³ μL^-1). Other platelet index values range between 0.09-0.31% for PCT, 6.54-7.94 fL for MPV and 32.86-36.81% for PDW, with corresponding mean values of 0.2±0.13%, 7.24±0.84 fl and 34.84±2.36%, respectively. A significant correlation exists between PCT and platelet number, PCT and MCV and MPV and PDW. The results of this study provide baseline information for studies dealing with the physiological and clinical significance of platelet parameters in the mountain gazelle.

ACKNOWLEDGEMENTS

We are grateful to his Highness Prince Bandar bin Saud, Secretary General of the National Commission for Wildlife Conservation and Development and Dr Robbie Robinson, KKWRC Director, for encouragement and support.