The haematological measures in the present study are indicative of the nutritional stress and provide a hint for future studies. Measuring the haematological attributes may well be less time-consuming and less costly than any other nutritional assessments in the sheep herd, and that could be even applicable to the transhumance system. As sheep are grazing across the elevational gradient, frequent measures of such attributes might facilitate in balancing the feeds and nutritional status of different physiological stages of animals and for different purposes that further might acknowledge the standards of feed and nutrition management regime (traditional transhumance or modern stall feeding).
Transhumance is an extensive system of livestock farming. Animals under such extensive care might expend more energy for physical and ranging activities, compared to animals having a sedentary life under intensive management which may expend less. Sheep and goats managed under traditional husbandry practices have low haematological values compared to modern husbandry practices, regardless of age, sex, and climate (Coles 1986). So therefore, haematological analyses may be indicative for maintaining the least-cost based production for traditionally farmed or herded sheep in the Himalayan landscapes. Blood is an important index of physiological and pathological changes in an organism (Mitruka and Rawnsley 1977). The examination of blood gives the opportunity to investigate the presence of several metabolites and other constituents within the body of animals, and blood plays a significant role within the physiological, nutrition-associated pathological standing of an organism (Aderemi 2004). Haematology and serum biochemistry assay of livestock determines the physiological disposition of the animals to their nutrition (Menon et al. 2013). Deficiency of both macro- and micro-nutrients triggers enormous discrepancies in haematological and serum biochemical profiles of livestock animals (Onasanya et al. 2015). Data in the present study has clearly demonstrated that changes in nutritional quality in the pasture had an impact on blood haematological profile, and such a trend had also been reported by Šoch et al. (2011). However, it was obvious that the pasture species were different due to altitudinal variations. Furthermore, the altitude causes immune suppressions in sheep (Meehan 1987), which is, however, observed at low altitude (increased WBC count) because of a decline in herbaceous quality. The measurement of other metabolic stressors has to be considered in future when the pasture species varies with the elevational pasture sites, as was the case in the present study.
The haemoglobin (Hb) plays a very important role in physiological adjustment to cope with hypoxic environments at high altitude (Coles 1986), while the poorer herb quality and the difference in herbage species may induce low Hb/RBC at low altitude sites. Likewise, lower PCV values at low grazing altitudes indicated that the flock was vulnerable to anaemic conditions, and such trends had been previously reported in several experiments. The increased tendency of blood erythrocytes in domestic cattle at high altitude is a commonly reported phenomenon (Hays et al. 1978). In the present study, the high RBC values were observed at higher altitude. An increased number of RBC in sheep when the animals were exposed to a higher altitude seems the most important haematological acclimatization’s response reported to a low oxygen environment (Monge and Leon-Velarde 1991; Weber 2007). RBC count significantly increased at a higher altitude due to the erythropoiesis process; such trends had also been observed (Al-Samarai and Al-Jbory 2017) in Iraqi Awassi sheep. At high altitude, an increase in RBC and a decrease in MCV occurred at the same time in the total count; therefore, the total surface of RBC was enlarged, which was advantageous for Hb to bind oxygen (Bunn 1980). Therefore, the increase in RBC and also the decrease in MCV are also the common haematologic mechanisms for mammals and birds to adapt to high-altitude hypoxia (Wu et al. 2005).
A decrease in lymphocytes with increasing age and an increase in neutrophils with decreasing age, which were determined in sheep, could be related to the immune response at the advancing stage of age. The contrasting result might be due to the nutritional status, geography, and seasonal and meteorological variations in the grazing sites respectively. Age and site were found to have a significant effect on haematocrit and mean corpuscular Hb levels. HCT and MCH levels observed were higher in animals below 1 year age when compared to an adult. An identical result was illustrated by Egbe-Nwiyi et al. (2000) in Nigeria where he observed high HCT and MCH level in 0 to 6 months of sheep than an adult.
In the present study, Hb level and haematocrit values were found to be increased significantly at a high altitude, and such trends in domestic cattle had been reported by Zemp et al. (1989). Previous researchers had additionally concluded that an increase in RBC, Hb, and haematocrit percentage is a compensatory mechanism of reduced oxygen saturation at high altitude (Yersin et al. 1992). Further, it was also reported that Hb with high oxygen affinities in high altitude species occur more than those of low land relatives (Storz 2007); Baruwal sheep might have gained such high-altitude adaptation characteristics. Hypoxic condition at high altitudes regulates partial pressure of oxygen in arteries that alters the physiological phenomenon either by changing Hb concentration in blood or by changing the oxygen-binding affinity of Hb (Storz and Moriyama 2008; Storz 2016). The former mechanism is more important in acclimatization response of low land natives, and the latter one is more important in genetically hypoxia-adapted high land natives (Bunn 1980). Higher values of RBC, Hb, and haematocrit levels indicated the response mechanism of Baruwal sheep in response to hypoxic conditions at high altitude, that helps to improve oxygen delivery capacity. Further, the higher values might be indicative of the abundance and availability of the better quality pasture species at high altitude. Lower RBC, Hb, HCT, and PCV values at the low altitude could also be due to the unavailability of essential minerals in the diet, due to the scanty and lower herbage availability during the winter season. Low concentration of blood macro-minerals during winter in Tibet had been also reported by Xin et al. (2011). As a mechanism of high altitude adaptation, the increase of Hb concentration in blood at high altitude has been repeatedly reported in other domestic species such as in cattle (Zemp et al. 1989) and yaks and their hybrids with cattle (Barsila et al. 2014).
Acute stress during the adaptation period at higher altitude can increase stress hormone level, but while persistently living at the thermo-comfortable environment at the higher site with relatively high humidity, an abundance of quality forage and fodder after the acclimatization phase may normalize the WBC (white blood cell) values at higher altitude. Meanwhile, various factors such as colder environment, low humidity, nutritional deficiencies, and unavailability of feed resources during winter at low altitude increase cortical level, thereby increasing leukocyte values at low altitude as compared to high grazing site in transhumance Baruwal sheep.
In the present study, the leukocyte level was found significant with changing altitude. The higher leucocyte values at low altitude grazing sites might be the indication of nutritional and environmental immune suppression, as the pasture condition was completely brownish and withered. It has been reported that WBC are at lower levels in different breeds of cattle throughout summer compared to spring (Mirzadeh et al. 2010).
In the present study, greater values of leukocytes in the lower site during winter as compared to higher altitude may be due to the stress imposed on transhumance sheep. The stress hormones, particularly cortisol and adrenaline, enhance the rise in WBC count and exert differential effects on leukocyte counts (Cupps and Fauci 1982). Acute stressors, e.g. cold stress, and the poor nutritional status might activate the hypothalamic-pituitary-adrenal axis, resulting in increased cortisol levels (Dantzer and Mormède 1983). Experiments conducted earlier additionally found an explicit increment in cortisol level in an animal exposed to cold stress due to lipolysis and utilization of brown adipose tissue for maintenance of body heat (Himms-Hagen 1990).
The pathological causes of changes in MPV values were not shown in the present study; however, greater MPV values at low altitude indicated grazing on thorny vegetation or some reasonably physical pain in sheep during the herbage selection. Likewise, the decreased MPV at high altitude in summer would be a reflection of relatively tender vegetation available for grazing.