Heat stress Effects on Hematological and Biochemical Responses of Sheep and Goats
Satya Prakash Yadav*, Ajeet Kumar, Himalaya Bhardwaj
Bihar Veterinary College, Bihar Animal Sciences University, Patna, Bihar.
*Corresponding author: drsatya202118@gmail.com
The blood profile of animals is sensitive to changes in the environmental temperature and is an important indicator of physiological responses to the stressing agent. Determination of blood parameters may be important in establishing the effect of Heat Stress (HS). HS affects animals as revealed by changes in hematological parameters, i.e. red blood cells, white blood cells, hemoglobin, lymphocytes, neutrophils, eosinophils, monocytes, granulocytes, packed cell volume, and blood pH. When exposed to HS, goats showed an increased amount of red blood cells, packed cell volume, hemoglobin, white blood cells, neutrophils, eosinophils, lymphocytes, and monocytes. Also, packed cell volume, hemoglobin, and red blood cells were higher under HS in goats and sheep. In contrast, HS decreases packed cell volume and hemoglobin in sheep and goats, and white blood cells in goats. However, higher packed cell volume values are an adaptive mechanism of animals to provide the necessary amount of water, where more water is transported into the circulatory system, required for the evaporative cooling processes.
Another explanation of the increase in packed cell volume and hemoglobin levels could be either increased un-attack of free radicals on the red blood cells membrane, which is rich in lipid content and ultimate lysis of red blood cells, or availability of adequate nutrients for synthesis of hemoglobin as the animal consumes more feed or decreases voluntary intake under HS. The acid-base balance is a complex physiological process to maintain a stable pH in an animal’s body. The body utilizes different mechanisms to combat any change in acid-base balance, i.e. chemical buffering, respiratory adjustment of blood carbonic acid (H2CO3 ), and excretion of hydrogen ions or bicarbonate (HCO3-) by the kidneys. Metabolic acidosis and alkalosis involving HCO3- as well as respiratory acidosis and alkalosis related to the partial pressure of CO2 may occur under HS.
The vital limits of pH variation for mammals are between 7.35 and 7.45 and are regulated by a complex system of buffers (H2CO3 and HCO3-). Blood pH increased under HS in sheep and goats. The increase in pH may be due to reduced H2CO3, total CO2, HCO3- and base excess in blood and extra-cellular fluid. The secretion of HCO3- in urine and its reabsorption suggest a large requirement and turnover of body HCO3- to maintain blood pH during HS. Blood biochemical parameters reflect the health (detecting possible diseases) and the metabolic status of an animal (evaluating the body’s internal condition, the function of organs [e.g. kidneys and liver], and metabolic processes in the body), which are widely used in clinical situations.
HS affects biochemical parameters, i.e. alkaline phosphatase, alanine aminotransferase, aspartate transaminase, lactate dehydrogenase, total protein, albumin, globulin, glucose, cholesterol, blood urea nitrogen, non-ester fatty acids, beta-hydroxybutyrate, creatinine, triiodothyronine, thyroxine, cortisol, prolactin, sodium, potassium, chloride, calcium, magnesium, iron, manganese, copper, zinc and oxidative stress parameters (glutathione peroxidase, glutathione reductase, superoxide dismutase and lipid peroxides).
Enzymes Metabolic regulators are important in elucidating a picture of modulation in physiological mechanisms during stressed conditions and are best assessed by determining the enzymes governing various metabolic reactions in plasma/serum. Enzyme levels reflect the metabolic activities during stress. HS reduces alkaline phosphatase and lactate dehydrogenase activity in sheep and goats. The decrease in these enzymes during HS is due to the decrease in thyroid activity during HS. Serum levels of aspartate transaminase and alanine aminotransferase are helpful in the diagnosis of the welfare of animals. The serum alanine aminotransferase value increases during HS in goats. Proteins A Significant decrease in total protein concentration in goats has been reported during HS.
Total plasma protein, albumin, and globulin levels decrease in goats subjected to HS. This may be due to an increase in plasma volume as a result of HS, which results in a decrease in plasma protein concentration. In contrast, HS increased total protein and albumin in goats and could be due to dehydration which has been reported to occur as a result of increased respiration rate.
Studies on glucose, cholesterol, blood urea nitrogen, non-ester fatty acids, and beta-hydroxybutyrate in response to HS are conflicting. Glucose and cholesterol levels show greater differences under HS conditions than in the comfort zone. HS conditions decrease glucose and cholesterol levels in goats. The decrease in glucose level could be related to the decrease in the availability of nutrients and the lower rate of propionate production. or due to the increase in plasma glucose utilization to provide energy for muscular expenditure required for high muscular activity associated with increased respiration rate. The decrease in cholesterol level may have a relation with the increase in total body water or the decrease in acetate concentration, which is the primary precursor for the synthesis of cholesterol. Exposure to HS resulted in higher non-ester fatty acids in sheep and beta-hydroxybutyrate concentration in goats.
