HEAT STRESS ABATEMENT RESPONSES IN PRODUCTIVE ANIMALS
T.Kavin1, *, V. Leela 2, K.Rajamanickam 3, P.Visha 4, S.Alimudeen5
1- Post graduate research scholar, Department of Veterinary Physiology, Madras Veterinary College, TANUVAS.
2 – Professor and Head, Department of Veterinary Physiology, Madras Veterinary College, TANUVAS.
3 – Assistant Professor and Head, Department of Veterinary Physiology and Biochemistry, Veterinary College and Research Institute, Salem.
4 – Professor and Head, Department of Veterinary Physiology and Biochemistry, Veterinary College and Research Institute, Salem.
5 – Post graduate research scholar, Department of Animal Husbandry and Veterinary Extension, Kerala Veterinary and Animal Sciences University.
* – Corresponding author
kavint2013@gmail.com
Introduction
Optimum temperature is essential for the animal to show their maximum productivity in the aspect of milk and meat production. Genetic and epigenetic factors determine the productivity of animals. Among the various epigenetic factors, the environment has huge effect on productive traits. The environmental factors include air temperature, relative humidity, wind speed, and solar radiation. The temperature has an important role in animal productivity. Based on the fifth assessment report of IPCC, global temperature increases range between 0.3 to 4.8 o c by the year 2100. It indicates that environmental temperature increases as the year progressing. Changes in environmental factors will affect animal productivity due to their adaptive mechanisms.
Heat stress
Temperature severely affects animal productivity and health in the form of heat stress as compared to other factors. Temperature humidity index is an essential factor to identify heat stress in animals.THI ranges vary from 70-90. The optimum THI index for bovine is 72. Whenever THI index exceeds THIs level animal felt the heat stress condition. Generally, thermal stress is encountered by the animal when the temperature exceeds between the upper or lower critical temperature of animals requiring an increase in basal metabolism to maintain the normal homeostasis of the animal. Three major mechanisms elicited by the animal to maintain homeostasis are mentioned in Table-1.
| Mechanism | Response |
| Acclimation | Phenotypic response to specific stressor |
| Acclimatization | Long term physiological adjustment to multiple stressors |
| Adaptation | Systemic responses to stressors |
The mechanisms of adaptation include behavioural, physiological, and biochemical changes to overcome the stressor responses. The major physiological responses in animals during heat stress include body core temperature, skin temperature, sweating rate, respiration rate, feed intake, and productive performance. The adaptive mechanism could trigger the changes at the cellular level to produce certain kinds of proteins like heat shock protein (HSP) which aids the cell viability during adverse environmental conditions.
Body temperature
Heat stress will increase the body core temperature of the animals. Especially in cows, rectal temperature, rumen temperature, subcutaneous tissue temperature, and milk temperature. Vaginal temperature strongly correlates with rectal temperature at the same time vaginal temperature is least affected by external factors. In practice, rectal temperature is used as a sensitive index to identify heat stress in normal healthy animals. It positively correlates with THI index of the environment. Panting and sweating are the two primary systemic responses exhibited by the animal during heat stress. Buffaloes are easily susceptible to heat stress due to their anatomical confirmations like dark skin, less number of sweat glands, and sparse hair coat. Buffaloes are easily susceptible to heat stress than cattle. Hence buffalo requires additional factors like wallowing to ameliorate the heat stress condition. Behavioural response in distressed animals may seek shade places, change its orientation to the solar radiation and increase the water intake.
Respiratory rate
High ambient temperature will increase the respiration rate to enhance the evaporative heat loss in stressed animals. The respiratory rate significantly increased in heat-stressed animals compared to those in the thermo neutral zone. Respiratory rate will increase up to 3-4 folds in heat-stressed animals. Respiratory rate will significantly increase during the summer season compared to the spring and winter seasons. Increased oxygen demand during heat stress will result in an increased respiratory rate. Wallowing in buffaloes and providing fans and sprinkles will reduce the heat stress in order to that it will decrease the respiratory rate towards the normal range.
Heart rate and pulse rate
Heart rate and pulse rate are increased during the warm season due to their high THI index. Up surge in pulse rate and heart rate could increase the blood flow in the peripheral circulation to enhance the heat loss through conduction, convection, and radiation mechanism to the surrounding environment thereby maintain the homeostasis of animals during thermal stress.
Water intake and hydration status
Increased water intake in animals due to dehydration occurs during massive sweating to maintain the thermoregulatory mechanism. Increased core temperature causes increased peripheral circulation thereby increases skin temperature.it results initiate the various heat-dissipating mechanism leads to massive sweat gland secretion reduces the body hydration status of the animal. It will stimulate the Thirrst center in the hypothalamus results increased water intake of animals during heat load situations.
Neuro-endocrine responses
Heat stress triggers the neuro endocrine response cause changes in the circulatory hormones level especially cortisol and catecholamines to regulate the body energy metabolism. Major hormones responsible for thermal adaption are mentioned in the Table-2.
| Hormones | Circulatory level during heat stress |
| Cortisol | Increase |
| Thyroxine | Decrease |
| Prolactin | Increase |
| Insulin | Decrease |
| Growth hormone | Decrease |
Molecular responses during heat stress
Heat stress stimulates the production of a conserved family of proteins known as heat shock proteins (HSP) in all livestock species. Heat shock protein is a molecular chaperone involving the regulation of protein production.it will be expressed by the major cellular systems includes skeletal myocyte, hepatocyte, lung cell, kidney cell, adipocyte, blood cells, and myocardial cells. HSP maintains cellular integrity and viability during heat stress conditions. Major HSPs expressed during heat stress are HSP10, HSP27, HSP40, HSP60, HSP70, and HSP90. HSP70 is the most predominant HSP expressed in all cellular systems during heat stress.
Conclusion
Heat stress in productive animals affects milk and meat production during high ambient temperature conditions. Alterations in behavioral, physiological, neuroendocrine, and cellular responses provide thermal adaptability in animals. most of these responses could possibly ameliorate the drawbacks in the heat stress condition in productive animals and ensure their individual production capacity. Heat stress in productive animals affects milk and meat production during high ambient temperature conditions. Alterations in behavioral, physiological, neuroendocrine, and cellular responses provide thermal adaptability in animals. most of these responses could possibly ameliorate the drawbacks in the heat stress condition in productive animals and ensure their individual production capacity.
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https://dairy.extension.wisc.edu/articles/animal-handling-during-heat-stress/
