Among all the morphological parameters, body height, body length and neck length were significantly higher, whereas girth of shank was lower in low lander Dromedarian as compared to native high lander Bactrian camels (p<0.05; Table 1). This variation in morphological parameters could be due their breed characteristics, as there body size is different in all the habitats. However, no significant variation was recorded in height of hump, distance b/w the eyes, girth of abdomen, and face length (p>0.05). Interestingly, body height, body length, height of hump were within the normal range of Dromedary, but lies towards higher side. Moreover, hump girth, and skin thickness of abdomen and shank were significantly higher in low lander Dromedarian as compared to native Bactrian (p<0.05). These are important morphological adaptation parameters which varies in cold and hypobaric hypoxia environment (Faye et al., 2001). The skin thickness and hump size are dependent on subcutaneous deposition of adipose tissue, which are primary source of non-glucose energy substrates in animals adapted to cold environment at high altitude (Faye et al., 2001; Kamili et al., 2006). Hence, these finding are indicative of morphological adaptation process of Dromedarian to cold oxidative stress conditions. However, high lander Bactrian camels have adapted very well in these conditions as indicated by lower girth of hump and skin thickness as compared to low lander camels. In the present study, these low lander Dromedarian camels were introduced to high altitude two years back. Hence, these Dromedarian camels were under the process of adaptation, and exhibited higher girth of hump, and skin thickness at shank and abdomen region. Various reports in literature have studied the morphological diversity in Ethiopian camels and Southern Moroccan camels to identify homogeneous groups depending on their body measurements (Higgins and Kock, 1984; Yosef et al., 2014; Boujenane et al., 2019). However, to the best of our knowledge there are no reports in literature on morphological parameters study of Bactrian camels. This is the first report on comparative study of all morphological parameters indicative of adaptation in low lander and native high lander camels to high altitude region. These morphological parameters and their reference ranges can also be helpful in the evaluation of overall growth of animal for further selection of elite breeds for logistic purpose e.g. endurance exercise, load carrying and patrolling.
Among all the physiological parameters, heart rate was significantly high, whereas the rectal temperature was low in Dromedarian camels than the Bactrian camels (p<0.05; Table 1). The heart rate and rectal temperature were within the normal reference range in native Bactrian camels. However, low lander Dromedarian camels showed very high heart rate which lies beyond the reference range of camel. This parameter at higher level is an indicative of adaptation changes in Dromedarian camels. High altitude stress conditions induces hormonal and neuronal changes in body by increasing the sympathetic nervous system activity (Simmonyi, 2014). This leads to a significant increase in blood pressure and heart rate in Dromedarian camels at high altitude. Interestingly, the rectal temperature was lower than the normal reference range in Dromedarian camels, which is indicative of poor energy metabolism. The body homeostasis is an important indicator of physiological status of animal adaptation to particular environment (Mohammed et al., 2007). However, both these parameters were within the normal range in Bactrian camel. These findings revealed that Bactrian camels are more adapted to these extreme conditions than the low lander Dromedarian camels even after two years of rearing of low lander at high altitude. The body temperature and heart rate are dependent on body metabolism and animal response to stress. Therefore, heart rate and rectal temperature of Dromedarian camel indicates these animals are having poor metabolism and adaptation response to stress prevalent at high altitude. Similar observations have been recorded in earlier reports on camels (Higgins and Kock, 1984; Al-Haidary et al., 2016).
Among all hematological parameters, platelets, ESR and lymphocytes levels were significantly high in native high lander Bactrian camels (p<0.05; Table 2). However, total leukocytes and neutrophils count were higher in low lander Dromedarian as compared to Bactrian camels (p<0.05). There was no significant variation in hemoglobin (Hb), PCV, erythrocytes, monocytes, eosinophil, basophils, MCV, MCH and MCHC levels between the two breeds of camels (P>0.05). The erythrocyte size of Dromedarian camel was significantly higher than the Bactrian camel (p<0.05; Table 2 and Fig 1, 2). Blood Hb concentration and erythrocytes count were almost similar and within the range in both the breeds.
Despite similar erythrocyte count and Hb levels, MCV (mean corpuscular volume) values in Dromedarian camels were greater than the Bactrian and normal reference range reported in literature (Table 2). This may be due to large size of immature erythrocytes which are also known as reticulocytes (Fig 2). The reticulocytes are capable of more cellular oxygen transport due to their high affinity to oxygen. The low lander Dromedarian camel rearing at high altitude need more efficient cellular oxygen transport system to adapt under hypobaric-hypoxia conditions of high altitude (Adili et al., 2013). The microscopic size measurements also revealed larger size of erythrocytes in Dromedarian camel (Fig. 2). The large size of erythrocytes are indicative that low lander camels are under the process of haematological adaptation to hypobaric hypoxia prevalent at high altitude (Banerjee et al., 1962).
The total leukocytes count was significantly high in low lander Dromedarian as compared to native Bactrian camels. Increase in leukocytes count could be due to compromised immune system under stressful conditions (Su et al., 2018). More leukocytes are required to cope up with these severe environmental stress condition in order to survive. Therefore, this increase in leukocytes count could be due to stress factors prevalent at high altitude hypoxia conditions, which triggers immune response for homeostasis maintenance (Ouajd and Kamel, 2009). However, low leukocytes count in Bactrian camel along with higher lymphocytes counts are indicative of better adaptation response to high altitude.
The morphological changes in neutrophils in the form of band shaped and segmented neutrophils were observed in both the breeds of camels (Fig. 1 and 2). However, these morphological changes and neutrophils number were significantly high in Dromedarian camels as compared to Bactrian camels (Table 2), whereas the number of lymphocytes were high in native Bactrian camels. These findings are indicative of free radicals generation and immunosuppression under high altitude stress conditions. (Zongping, 2003; Ouajd and Kamel, 2009). Various studies observed that more neutrophils are released to counter oxidative stress-induced free radicals and microbial infections (Higgins and Kock, 1984). Moreover, neutrophils number increases in acute response to stress conditions, whereas lymphocytes number increases in chronic response conditions (Klokker et al., 1993). This indicates that low lander camels are under the process of adaptation in response to high altitude, while high lander camels have adapted very well in these conditions resulting in lower neutrophils and higher lymphocytes count. Since, these high lander Bactrian camels are bred and reared for several generations under high altitude stress conditions, all these changes are likely to be acquired by them in response to high altitude conditions over several generations.
In the present study, the level of platelets were significantly high in both the breeds of camels, which could be due to stimulation of platelets precursors cells in response to hypoxia conditions at high altitude (Table 2). There is competitive response between stem cells of erythrocyte and platelets precursor cells. Hence, increase in platelets number is an indicative of adaptation changes to hypobaric hypoxia. The normal hematological findings reported here will be useful in the studies of clinical conditions of the camel at high altitude region. Several investigators have studied the hematological parameters and their reference ranges in camels in hot desert regions for clinical interpretation of data (Banerjee et al., 1962; Farooq et al., 2011; Elitok and Cirak, 2018; Islam et al., 2019). However, detailed studies of hematological parameters at high altitude region have not been carried out so far.
Biochemical and oxidative stress parameters
The biochemical parameters showed significantly higher level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and creatinine, whereas significant decrease in glucose and triglycerides levels in native Bactrian as compared to Dromedarian camels (p<0.05; Table 3). However, other parameters viz. albumin, total protein (TP), calcium, magnesium, uric acid and iron remain unaffected (Table 3). The high AST and ALT levels in Bactrian indicates that the liver metabolism is highly active under stress at high altitude region which releases more ALT and AST level into the blood during adaptation (Aragon & Younossi, 2010). Slightly higher creatinine and urea level in native Bactrian camels indicates more active renal metabolism, which might be a adaptive mechanism of water conservation in high altitude cold stress conditions (Samra & Abcar, 2012). Liver metabolism is a vital physiological process to maintain body homeostasis to fulfill cellular function under stressful conditions. The animal susceptible to environmental stress conditions have poor metabolism, and therefore their body temperature is lower than the normal, and they are more prone to stress mediated ailments. In present study, low lander camel has significantly low rectal temperature than the Bactrian camels and normal reference values, which is an indicative of poor liver metabolism at high altitude. Hence, our findings supported the hypothesis of higher liver and kidney metabolic activity required for metabolic adaptation to high altitude.
Interestingly, total serum glucose levels recorded in native Bactrian camels were very low as compared to Dromedarian camels (Table 3). Earlier reports have documented that exposure to high altitude region leads to transient increase in glycemic index initially, this could be an adaptive mechanism to low energy level which is effective in camel at high altitude (Brooks et al., 1991; Larsen et al., 1997). However, prolonged and continuous exposure to high altitude lowers glycemia in serum (Brooks et al., 1991). The acclimatization to high altitude seems to be the main reason for the increase ATP fuel dependency from non- glucose energy sources. Under cold stress, non-glucose energy substrates are more important and generally preferred for ATP generation. At high altitude, the glucose based energy diets are avoided and protein-fat based diets are preferred as adaptation mechanism for cellular energy generation. In present study, low glucose level were observed in native Bactrian, which is an indicative that native Bactrian camels are more dependent on non-glucose energy substrates. Whereas, high triglycerides and glucose levels were present in low lander camels, which shows that the energy metabolism in Dromedarian is more dependent on glucose and triglycerides rather than protein-fat diet. This further support the hypothesis that low lander camels are poorly metabolically adapted to high altitude conditions. All these important findings indicated the effect of climate on biochemical parameters, which is an important indicator of metabolic adaptation behavior in camel at high altitude (Omidi et al., 2015; Elitok & Cirak, 2018; Islam et al., 2019).
The present study observed no significant difference in oxidative stress markers, DPPH, and FRAP between low lander and high lander camels from different origins (Table 3). The high antioxidant levels help in reducing oxidative stress generated cellular damage in camels induced by high-altitude adverse conditions (Kumar et al., 2019). Hence, the oxidative stress reducing ability to protect important biomolecules like DNA, RNA, proteins, carbohydrates and lipids in their functional active state was very well documented in camels serum samples. These results suggests the importance of estimation of antioxidant parameters for monitoring health status and endurance parameters. In conclusion, the current study helped in understanding of morphological, haematological and physio-biochemical adaptation mechanism in camels to high altitude environment. These variations could be due to diversity in genetic makeup, environmental factors and altitude effect.