मवेशियों में ग्रीष्मकालीन तनाव को कम करने के लिए व्यापक रणनीतियाँ
The inability of the animal to release enough heat to sustain homeostasis leads to heat stress. The ability of animals to disperse heat is compromised by high ambient temperature, relative humidity, and radiant energy. Animal health and productivity may be impacted by heat stress, particularly when air temperatures rise.
Heat stress is becoming more prevalent, especially in tropical regions. Animal production suffers significant financial losses as a result of heat stress. The intake of feed, growth rate, egg production, reproduction efficiency, and production efficiency as measured by weight gain or milk yield per unit of feed energy are all impacted by heat stress.
There hasn't been enough research done on the physiological reasons underpinning how heat stress affects domestic animals' declining output performance.
Impact of Heat Stress on Zebu Cattle
Bos taurus breeds are less adept at controlling body temperature under extreme heat stress than Bos indicus breeds due to variations in metabolic rate, water and food consumption, sweating rate, coat characteristics, and color.
Bos indicus has a higher density of arteriovenous anastomoses than vascular tubes including capillary networks, which reduces tissue resistance to heat transport from the core of the body to the surface and promotes enhanced blood flow to the skin during heat stress (Hales et al., 1978).
Additionally, to maintain normal body temperatures, Bos taurus need to drain significantly more sweating than Bos indicus due to their higher skin heat loading.
Zebu cattle's bright, shiny, and smooth coats also contribute to a decrease in heat exchange through radiation (Hutchinson and Brown, 1969). Heat stress and providing shade for feedlot cattle are welfare problems. Cattle highly seek shade in hot weather, which can lower the radiant heat load by up to 30%.
General Effects of Heat Stress
1. Major signs of Heat Stress:
Respiration rate
80 to 120 / minute- moderate heat stress,
120-160 / minute- moderate-severe heat stress;
>160 breaths/ minute severe heat stress,
seeking shade, refusing to lie down, reduced feed intake, crowding around water trough, body splashing, agitation and restlessness, reduced or no rumen contractions, open-mouthed panting/gasping, excessive drooling of saliva, recumbency, collapse, convulsions and coma, death.
2. Other signs:
restlessness, reduced rates of GIT motility, lethargy, reduced weight gain in growing animals, frequent laminitis, increased incidence of milk fever, uterine prolapse, mammary gland infections, uterine infections, udder edema, increased sweating, water intake, rectal temperature, reduced heart rate and drop in milk production.
Water and Electrolyte loss during Heat Stress
Sweating and panting cause the body to lose water and electrolytes (K and Na) due to evaporation when under heat stress. Urinary Na excretion balances excess K loss, preserving the proper ratio of K to sodium ions.
Additionally, panting causes a loss of CO2 that results in respiratory alkalosis, which is made up for by the excretion of HCO3 in the urine.
Proper management to reduce heat stress:
These steps are classified into the following categories-
1. Feeding and Watering Management
The greatest number of locally accessible, low heat increment diets—such as highly digestible, low fiber, low protein, and high-calorie feed—should be included in feeding plans throughout the summer.
Rumen degradable protein should be avoided to increase the availability of high-quality protein during the hot season. Yeast cultures, fungal compounds, and buffers are examples of digestive and rumen stabilizing aids that ought to be used.
Niacin, enzymatic antioxidants (such as catalase, superoxide dismutase, and glutathione peroxidase), non-enzymatic antioxidants (such as vitamins C, A, and E), proteins (such as transferrin and albumin), peptides (such as glutathione), zinc, and chromium, and feed supplements are crucial for preventing heat stress.
Feeding frequency should be higher but bulk feeding at a time and sudden changes in ratio composition should be avoided.
2. Housing Management
As moisture from their leaves evaporates, trees provide great natural shading that reduces heat from the sun and cools the air around them. To effectively manage heat stress, permanent shades should carefully take into account factors including direction, floor area, height, ventilation, roof and wall construction material, feeding and watering facilities, and waste disposal system.
Animal heat load will be decreased by light-colored walls that reflect the most solar radiation, low stocking density, enough air movement, cooling pads, foggers, misters, sprayers, sprinklers, and fan cooling systems.
3. Milking Management
Reduced milking time, milking during cooler times of the day, decreased animal density, avoiding animals walking long distances to reach the milking parlor, providing drinking water, physically altering the parlor, and other measures should all be taken to lessen heat stress in the milking parlor.
4. Health Management
Deworming, routine shed cleaning and disinfection, preventing water logging, caulking crevices and gaps, and boosting sunshine exposure and ventilation in animal sheds are all examples of preventive actions that should be implemented.
5. Breeding Management
The goal of the breeding strategy should be to create breeds that retain the ideal balance between productivity and heat tolerance through selective breeding via regulated mating.
Moreover, embryo transfer technology can address issues with quiet or absent oestrus, low conception rates brought on by heat stress, and infertility.
The roles of genes and molecules involved in thermo-tolerance and thermo-sensitivity (Heat shock protein, HSP-70) are being identified and understood through the use of genomic and proteomic techniques.
Conclusion
Farmers have a very difficult challenge during the summer months of keeping the livestock healthy and productive. Heat-related losses in milk production result in significant financial losses for our nation each year. Better feeding, housing, health, and breeding management practices can reduce productive loss and the impact of heat stress on livestock.
References
Hales, J. R. S., Iriki, M., Tsuchiya, K., & Kozawa, E. (1978). Thermally-induced cutaneous sympathetic activity related to blood flow through capillaries and arteriovenous anastomoses. Pflügers Archiv, 375(1), 17-24.
Hutchinson, J. C., & Brown, G. D. (1969). Penetrance of cattle coats by radiation. Journal of Applied Physiology, 26(4), 454-464.
Authors:
Karishma Choudhary and Vinod Kumar Palsaniya
V. Sc (LPM), CVAS, Navania, Udaipur.
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