Plasma glucose
The overall mean values of plasma glucose (m mol L
-1) of female
Marwari sheep during moderate ambience and cold ambience were 2.82 and 3.08 (Table 1). The overall mean values of plasma glucose showed a significant increase (9.21%) as compared to moderate ambience. The range of per cent increase was 3.95 to 11.48 (Fig 1a). Maximum and minimum increases were observed in the mean values of 2.5 BCS and 4.0 BCS. All the categories of BCS in the present study showed significant effects of ambience on plasma glucose, indicating that cold affected the animals regardless of body composition in relation to body muscle and fat. Cold conditions function as stressors to the animal and there is increased secretion of glucocorticoids in animals. Glucocorticoids are well known for their gluconeogenic effect thereby increasing the blood glucose level and decreasing its peripheral utilization in stressed animals. Small ruminants have been found to exhibit elevated plasma glucose concentrations in cold environments
(Zhang et al., 2022; García et al., 2020). The remarkable influence of glucose levels on all categories of sheep and goats were probably caused by increased energy consumption during cold stress (
AL-Musawi et al., 2017). Higher blood glucose levels to the increased feed intake as a result of increased metabolism during extreme cold ambience
(Maurya et al., 2013). Increased blood glucose levels helped the animal to fight against cold stress. Increased cortisol activity leads higher blood glucose levels during superimposed stressors in sheep (
Pareek and Kataria, 2020). Increased glucose levels were due to activation of sympathetic nervous system and an increase in adrenal cortical activity
(Avci et al., 2008). Catecholamine and glucocorticoids increase the glycogenolysis and gluconeogenesis and secondarily glycemia (
Ganong, 1998).
All the categories of BCS showed a significant increase in the values of plasma glucose. In the present study the glucose level was less in the sheep of low body condition score. The decrease in plasma glucose concentration was related to less availability of substrate for glucose formation in the body of energy depleted sheep. Cows in moderate-to-thin conditions require more glucose than cows in obese conditions due to their higher maintenance needs. Hence, the higher demand for glucose in low-condition groups’ blood glucose levels reduces
(Singh et al., 2009). Animals that have extremely excellent body conditions (3 to 5) may lose up to a point of body condition where they are unable to maintain appropriate blood metabolites, physiological responses and growth
(Maurya et al., 2012) .
Total plasma proteins
The overall mean values of total plasma proteins (g L
-1) of female
Marwari sheep during moderate and cold ambience were 60.91 and 57.14, respectively (Table 1). The overall mean values of total plasma proteins showed a significant decrease (6.18%) as compared to moderate ambience. The results indicated that there is excessive breakdown of proteins as an alternate source to meet the higher demand of energy during cold stress.
Halliwell and Gutteridge (1990) opined that total serum proteins and albumin are the potential targets of oxidative injury. Animals’ blood cortisol levels can be stimulated via the hypothalamic-pituitary-adrenal and sympathetic-adrenal medullary axis to maintain homeostasis in response to environmental changes
(Sejian et al., 2018). Cortisol enhances the proteolysis and decrease the level of proteins.
All the categories of BCS showed a decrease in the values of total plasma proteins with advancement of score. The range of per cent decrease was 3.46 to 10.54 (Fig 1b). Maximum and minimum decrease were observed in the mean values of BCS 4.5 (10.53) and BCS 2.5 (3.45). The minimum loss of total plasma proteins occurred in 2.5 BCS is suggestive of better sustainability and maintenance of protein reserve of animal. BCS 4.5 animals were most severely stricken by extreme cold ambience and lost their plasma pool of proteins.
Plasma creatinine
The overall mean values of plasma creatinine (µ mol L
-1) of female
Marwari sheep during moderate and extreme cold ambience were 71.35 and 76.82, respectively (Table 2). The overall mean values of plasma creatinine showed a significant increase (7.66%) as compared to moderate ambience. The normal values of metabolites can be affected by age and sex of animals. Metabolic status of the animal is reflected by levels of creatinine. Most of the creatinine excreted by urine originates from endogenous creatine. Creatine circulates in plasma and taken up by the muscles, where it stores energy in the form of phosphocreatine. In muscles phosphocreatine breaks to form inorganic phosphate and creatinine to provide energy. Serum creatinine is proportional to muscle mass (
Kreider, 2003;
Cirillo, 2010;
Samra and Abcar, 2012) and increasing level represents the development of animal. In present study maximum mean values of serum creatinine during extreme cold condition were 90.94. The phenomenon of increase in creatinine may be a consequence of increased skeletal muscle breakdown or due to increased protein metabolism.
All the categories of BCS showed a significant increase in the values during cold ambience. The range of percent increase was 6.08 to 13.89 (Fig 1c). The present study indicates the increasing levels of plasma creatinine with increase in BCS from 2.0 to 4.5 except 3.0. There was a non-significant change in the mean values of plasma creatinine in BCS 2.0, 2.5, 3.0 and 3.5 where as significant changes in mean values were observed in 4.0 and 4.5 BCS in respect to 2 to 3.5 BCS during moderate ambience. In the present investigation the mean values of plasma creatinine were maximum in 4.5 BCS. The high BCS indicates the increase body reserve which can be utilized to meet the requirement when nutrient supply is limited. During extreme cold condition the body reserves are mobilized to yield energy. The breakdown of reserves and combined effect of cold stress may be the reason for higher values of creatinine in the plasma.
Kazumasa et al., (1998) explained that creatinine was an intrinsic substance which played an important role in oxidative stress and its products can be used as markers of oxidative stress. The maximum per cent variations were observed in the mean values of 2.0 BCS indicating that there was no fat reserve and for energy purpose there was mobilization of intrinsic substance leading to increased plasma creatinine levels.
Plasma urea
The overall mean values of plasma urea (m mol L
-1) of female
Marwari sheep during moderate and extreme cold ambience were 6.81 and 7.41, respectively (Table 2). The overall mean values of plasma urea showed a significant increase (8.81%) as compared to moderate ambience. The range of per cent increase was 4.28 to 21.83 (Fig 1d). Maximum and minimum increases were observed in the mean values of 4.5 BCS and 2.5 BCS. Stress from extreme environments can affect the urea cycle (
Wotron,1971). Higher plasma urea showed increased hepatocyte activity, causing a profound effect during extreme cold conditions
(Nazifi et al. 2003). Earlier scientists also indicated the role of urea and possible development of oxidative stress due to extreme ambience.
Chena et al., (2008) correlated the serum urea with the parameters of oxidative stress. This may be due to the fact that as a part of the oxidative stress mediated solute-signaling pathway in tissues, urea increases the expression of oxidative stress responsive transcription factors and is therefore associated with oxidative stress.
All of the categories of BCS showed a significant increase in the value of cold ambience. In the present investigation, the mean values of plasma urea were maximum in 2.0 BCS. The values fell progressively and was minimum in 4.5 BCS. However,
Caldeira et al., (2007) and
Carlos et al., (2015) observed highest plasma urea in 4 and 3 BCS, respectively and below that BCS there was a decrease in the plasma urea values were found. The maximum percentage change was observed in the mean values of 4.5 BCS. Similarly, total serum proteins showed maximum per cent change in 4.5 BCS. By comparing both the results, it can be interpreted that the breakdown of proteins resulted in increased plasma urea values.
Plasma cholesterol
The overall mean values of plasma cholesterol (m mol L
-1) of female
Marwari sheep during moderate ambience were 1.52 and 1.73 respectively (Table 2). The overall mean values of plasma cholesterol showed a significant increase (13.81%) as compared to moderate ambience. The range of per cent increase was 10.96 to 18.47 (Fig 1e). Maximum and minimum increases were observed in the mean values of 2.5 BCS and 4.0 BCS. Higher cholesterol levels can be attributed to higher thyroid activity in cold ambience as an increase in BMR is required with the need for extra production of heat to maintain body temperature
(Kataria et al., 2000) which increases turnover of basic fuel molecules in the blood. When newborn lambs are exposed to cold environments, their brown adipose tissues and plasma lipid undergo dramatic changes. This elevated lipid levels during cold stress is caused by the expression of genes (UCP2 and CPT1B) linked to fatty acid oxidation and thermogenesis
(Baumgartner et al., 2022).
All the categories of BCS showed a decrease in the value of plasma cholesterol in both the ambience. Significant differences in the overall mean values were observed in BCS 2.0, 3.5 and 4.5. In the present investigation, the mean values of plasma cholesterol were maximum in BCS 2.0. These animals represent the minimum amount of body reserve as fat. The higher BCS group represents a great amount of fat as body reserve and they moved their body reserve in cold stress.
Caldeira and Portugal, (1991) observed significant changes in serum cholesterol only in increasing BCS state of animals, whereas in the other states, values remained unchanged, reflecting remarkable stability in concentrations because of structural roles. Increasing total cholesterol during the increase in BCS states may be due to greater availability of nutrients for their synthesis. Lower cholesterol values during food restriction may be explained by the sudden decrease in nutrient availability for synthesis and or a decrease in 3-hydroxy-3-methylglutaryl COA reductase by excess of hepatic ketone bodies (
Vernon and Peaker, 1983) and reduction in hepatic synthesis of cholesterol transporter lipoproteins
(Remesy et al., 1983).