उच्च उपज देने वाले मवेशियों में गर्मी तनाव प्रबंधन
Sustainability in livestock production system is largely affected by climate change. An imbalance between metabolic heat production inside the animal body and its dissipation to the surroundings, leads to heat stress under high air temperature and humid climates.
The foremost reaction of high yielding cattle under thermal weather is increases in respiration rate, rectal temperature and heart rate. It directly affects feed intake thereby, reduces growth rate, milk yield, reproductive performance, and even death in extreme cases. Dairy breeds are typically more sensitive to heat stress than meat breeds, and higher producing animals are, furthermore, susceptible since they generate more metabolic heat.
Heat stress suppresses the immune and endocrine system thereby enhances susceptibility of an animal to various diseases. Hence, sustainable dairy farming remains a vast challenge in these changing climatic conditions globally.
India is first in milk production in the world production, with 78 million metric tons of milk from57 million cows 39 million buffaloes. This was possible only due to large scale crossbreeding of local breeds and non-descript breeds of cattle. Now crossbred cows are emerging as in important dairy animals. Nearly 9 to 11% of all the cows in milk are crossbred. The crossbred animals are more susceptible to heat stress.
Heat stress in dairy animals is one of the leading cause of decreased production and fertility during summer months. In India, the summer temperature goes beyond 45℃ and the upper critical temperature of dairy cattle is 18℃. When the temperature exceeds 27℃ even with low humidity, the temperature is above the comfort zone for the high producing dairy cattle. Humidity plays significant role in heat stress.
The crossbred / exotic animals are more prone to the heat stress losses as compared to indigenous cattle and the animal exhibits responses like reduced feed intake, increase water intake, change in the metabolic rate / maintenance requirement, increased evaporative loss, changes in blood hormones concentrations and increase in body temperature.
This productivity loss during summer can be reduced substantially by adopting the following heat stress management coupled with good health management like proper summer-oriented housing, animal cooling system, development of breeds tolerant to heat stress and high energy feeding.
How to reduce heat stress
Methods to reduce heat stress are managemental practices and nutritional correction. Under managemental practices, emphasis should be given on proper water supply, proper animal housing to reduce or to manage heat stress. Dairy animals need to increase water intake during time of heat stress to dissipate heat through respiration and sweating.
Water consumption increases by as much as 50% as the environmental temperature rises. Water should be fresh, clean at 70- 86 oF. It should be close to shed with enough water space. Minimum of 3 inches of depth of waterer are necessary to accommodate cattle muzzle. Provide at least two water locations per group.
Proper animal housing
The cattle sheds in Indian conditions should be designed to reduce the heat load because heat stress cause more damage to animals compared to winter. Animal can tolerate winter condition up to 15℃ without any difficulty. But the temperature above 30℃ result in drop in milk production and breeding efficiency. Therefore, our cattle’s specially crossbreds must be provided with proper housing.
Theoretically speaking, the best type of animal shelter is a one where the micro-environment temperature remains within 15℃ to 25℃ and humidity level around 10-12 mm Hg. Shades of trees provides an ideal protection from radiant heat, but do not fit because of other reasons.
Principles for creating an optimum micro-environment within an around the sheds are directed to reduce heat gain and promote heat losses from structure of animal’s house by radiation & condition. Proper ventilation at ridge level keeps two or three walls open.
Feeding and nutritional management
Points to be consider while feeding animals during hot weather, as feeding frequency, (extra feeding) time of feeding, (cooler time of a day, adequate feeding space and plenty of cool water. Modification in ration can help to minimize the drop in milk production, decreasing forage to concentrate ratio, result in more digestible rations.
Feeding buffers such as sodium bicarbonate and magnesium oxide allow higher concentrate rations and can help in low fat milk syndrome also. Hot weather increases the need of certain minerals. Minerals are also more easily depleted during hot summer months. The increase in respiration and perspiration will cause an excessive loss of water, thereby reducing mineral levels.
Potassium can be increased to 1.3 to 1.5 percent of the total dietary dry matter, sodium to 0.5 percent, and magnesium levels increased to 0.3 percent. If less forage is consumed, and the forage is high in quality, the cow's rumination activity may decrease. Consequently, the proper use of buffers becomes important to maintain intake, ruminal pH, and milk production.
Do not overfeed highly degradable protein during hot weather it should be 18% or less. Supplemental fat can be added in ration to increase energy in take. Also avoid feeding excess fat, overfeeding causes problem with rumen function supplementing extra vitamins during summer has no added advantage.
Animal cooling system
Rise in ambient temperature activates sweat glands to produce sweat. Each gram of sweat evaporated from skin utilises 590 calories from skin surface (Latent heat of evaporation of water). This process of evaporation causes cooling of skin. A part form sweating animals increase their respiration rate. (Induced evaporation of moisture from mouth/ lungs).
Breathing of animals at a much faster rate to combat heat stress leads to panting. To reduce the metabolic heat load, animals reject feed and fodder. Use of water as cooling agent either directly on animal body or for cooling the shelter microenvironment is as widely accepted practice.
Water can be used for spraying the floor and roof of shelter periodically or continuously during peak hot hours which lower their temperature and consequently reduces the heat load on animals. Grass screens on sides of shelter when with water considerably cool down the air passing through them.
It requires proper cross ventilation. During summer, we can reduce heat load of animals artificially by spraying small quantity of water on their body at repeated interval of 15-30 minutes. Fans or blowers fitted in cow she helps in increasing rate of evaporation of water. Skin cooling to the extent of 8 to150 C is achieved depending upon relative humidity.
Zero energy cooling
Cows having access to sheds with evaporated coolers had marked higher breeding efficiency than cows having access to only conventional sheds. The milk production is group maintained under cooled shed was 1.8 kg more per head than in conventionally shaded group.
Treatment
Immediate veterinary aid should be provided to the suffering animal. In the meantime, the animal shall be moved to a cooler place, given bath with cold water or wrapped in wet sheets and provided with fan.
Climate change characterized by a gradual incline in global temperature and frequent occurrence of extreme weather events is becoming a global issue that has significant impacts on performance and welfare of dairy cattle. In addition to impairment of lactational performance, heat stress has substantial impacts on a dairy cow's immune function and health at all stages of her life cycle.
During lactation, the summer season is associated with increased disease incidence in cows, which may partially result from reduced immune cell function under heat stress. The loss of electrolytes via skin secretions has to be minimized by improvement of housing and cooling of the animals.
Hence, the proper managemental practices is must require to maintain the productional efficiency of cattle during heat stress.
Authors:
Anjali, Lipika Sarma, Priyanka M. Kittur, Rishi Nanda
Division of Physiology and Climatology
ICAR-Indian Veterinary Research Institute, Izzatnagar-243122, India
Email: <