By -Dr Ravindra Bharati, TVO, Buxar,
Heat stroke or Hyperthermia can be a common issue for all type of livestock. In most part of India where high ambient temperature occur during the summer months, the farmer must provide living condition which give protection from excessive heat.
Dairy cattle are unable to dissipate their heat load efficiently. Their sweating mechanism is poor and they rely on respiration to cool themselves. A further disadvantage is the fermentation process within the rumen generates additional heat that cattle need to disperse. As they cannot get rid of heat effectively they accumulate a heat load during the day and dissipate heat at night when it is cooler.
When cows cannot dissipate their body heat, in addition to depressed feed consumption, heat stress has also been shown to have an effect on milk production and composition including milk protein and butterfat content.
Heat stress has a dramatic impact on feed consumption and milk production. It is not only related to ambient temperature but also associated with humidity and air movement. When the humidity increases the cows evapo-transpiration is reduced and the animal cannot cool itself. This inability to cool itself increases the core body temperature and greatly depresses feed intake.
Dairy Cattle Temperature Humidity Index ———–
Temperature alone is not a good way of measuring heat stress. Various indexes have been developed which take into account such factors as ambient temperature, relative humidity and evaporation rate. These are known as THI (Temperature Humidity Index)
Dairy Cattle Zone of Comfort ————
The “Zone of Comfort” of Bos Taurus cattle range between a range of 4ºC – 24ºC (39° F- 75° F). Within this temperature range dairy cows are most efficient.
The “Zone of Comfort” of Bos Indicus e.g. Zebu, is 10°C (50 °F) to 27°C (81° F).
Each genotype has a different and characteristic “zone of comfort” Science has established that under heat stress conditions, Bos Indicus breeds and their crosses have better heat regulatory capacity than Bos Taurus breeds, due to differences in metabolic rate, food and water consumption, sweating rate, and coat characteristics and colour.
Heat Load in Dairy Cattle————
When the temperature increases above 24ºC (75°F) the deep body temperature of the cow rises and production is depressed. Research has shown that this effect is aggravated if relative humidity is in excess of 45%. Once the Temperature Humidity index (THI) reaches 78 there is a significant decline in milk yield
Experimentation has shown that exposure to 40°C (104°F) for 7-10 hours will induce severe panting, gasping and drooling, sweating and drastically increased water consumption.
When the relative humidity exceeds 50%, the dissipation of heat by evaporative cooling becomes much more difficult and signs of heat stress develop sooner.
Any deviation from optimal (Zone of Comfort) conditions results in physiological behavioural stress adaptation which is made at the expense of production – decreased live weight gains and reduced feed conversion efficiency are the readily-measured outcomes.
As this stress adaptation develops, diversionary activity within cells and in their membranes escalates, to protect their structures and productive machinery from heat damage. Cellular metabolism is disturbed and membranes close down some of their operations altogether.
As a result of these physiological responses there are changes in acid- base balance, there is loss of homeostasis and the frank loss of key electrolytes (Sodium, Potassium and Bicarbonate).
If the severity of the stress progresses, lethargy, lassitude, weakness, stupor, staggers and death may result.
Visible signs of Heat Stress in Dairy Cattle————-
Decreased activity.
Animals seek shade and/or wind.
Refusal to lie down.
Increased respiratory rate (open mouth panting).
Open mouth and laboured breathing.
Sweating and excessive drooling.
Reduced food intake.
Agitation and restlessness.
Thirst is increased. Drinking water intake increases markedly (5 times temperate climates).
Increased urination (with heavy electrolyte loss).
Crowding over the water troughs.
Excessive salivation.
Milk yield drops by as much as 50% or more. (Milk Yield – at 35ºC there is up to 33 % depression and at 40ºC, as much as 50 %.).
Loss of milk quality – fat and protein content declines.
Loss of body weight.
The incidence of milk fever increases.
Metritis is more widespread.
Uterine prolapse is more common.
Mammary gland infections increase.
There are increased uterine infections.
Udder oedema is more severe.
Laminitis is more frequent.
Keto-acidosis is a recurring problem.
Fertility is lowered – insemination success rate falls. Increased somatic cell counts and risk of Mastitis.
Embryo mortality increases.
Calves are often premature and small.
Growing animals have markedly reduced weight gains.
Inability to move.
Collapse, Convulsions, coma.
Invisible signs of heat stress in Dairy Cattle———–
Ruminal pH is typically lower in heat stressed cattle. Rates of gut and ruminal motility are reduced, thus slowing passage of feed through the digestive tract.
Increased peripheral blood flow.
Some indigestibility of feed.
The huge water flux resulting from increased water consumption also causes heavy loss of electrolytes. Potassium (K+ ) loss from the skin increases by 500% in unshaded cattle. In attempts to conserve K+, cows increase urinary excretion rates of sodium (Na+).
Alter the production of reproductive hormones essential for pregnancy. Changes the balance of developing follicles in the ovary.
Embryonic development is affected.
Bicarbonate (HCO3) is lost.
Stress hormones appear in the blood.
Gene function is disturbed.
Heat shock proteins are activated to shut down metabolic reactions and to protect heat-sensitive tissues.
Responses to intercurrent diseases or pathogens decline rapidly.
Resources being diverted to unproductive efforts by the animal to restore balance (homeostasis).
All production is stopped due to loss of homeostasis.
The animal has done all that it can do to stop deep body temperature from rising and assistance is needed to restore, and retain, electrolyte balance to the optimum range.
Heat stress is acidogenic and on the acid side of pH 6.8 there is probably widespread cell damage.
Dietary management——
Whenever feed intake decreases due to heat stress, nutrient concentration should increase to maintain adequate intake of all required nutrients. Low quality, stemmy forages generate more heat by fermentation inside the rumen. High quality forages are digested faster and result in less heat being produced.
Increasing the energy density might entail the use of greater amounts of concentrate and/or by-products. Increasing the energy density of the diet, using high quality forages and feeding more concentrates should help the animal maintain her energy requirements even though she consumes less dry matter.
However, care should be taken to balance diets properly in order to avoid digestive disorders such as acidosis and displaced abomasums.
Factors that can contribute to rumen acidosis problems are:
1. Decreased DM intake with lower proportion of forage and higher levels of fermentable carbohydrates.
2. Decreased rumination.
3. Decreased saliva to the gut, a source of bicarbonate, with a reduction of its buffering power due to increased CO2 expelled (panting).
4. The decreased rumen pH impairs fibres digestion efficiency: rumen fibrolytic bacteria are the most affected when rumen pH drops (below 6.0).
5. Poor mixing of feed, allowing cows to selectively eat.
All of these factors contribute to decreasing feed efficacy, and, consequently, milk yield, and often milk fat. Moreover, acidosis has been shown to affect the animals overall health status, fertility, and bovines longevity.
Treatment———
First, animals are move away from direct sunlight to cool area. Treatment goal is to manage the hyperthermia provides cardiovascular support and to treat complication associated hyperthermia. The prevention of myocardial injury gives the corticosteroid intravenous (i/v). To minimized complication of bacterial translation and sepsis by given the anti microbial therapy .The cows are treated with Inj.dexamethasone2 10ml(i/v), Inj. Oxytetracycline3 5-10mg/ kg bwt dilute in 4lit.NSS (i/v), Inj. vitamin B1, B2, B6 ( Tribivet1 15 ml) (i/v). Next to start, cool water (but not cold water) is sprinkle on the animal body .
Cooling method Six step of cooling method;
(A) The cool water is sprinkling continue for 15 minutes and stops for 5 minute,
(B) The cool water is sprinkling continue for 10 minutes and stops for 5 minute,
(C) The cool water is sprinkling continue for 10 minutes and stops for 5 minute,
(D) The cool water is sprinkling continue for 8 minutes and stops for 3-4 minute,
(E) Check the rectal temperature, (a) if the temperature above the 104 0 F, to continue sprinkle the cool water and follow up the above step no A,C,D.(b) if the temperature around the 1030 F follow up next step,
(F) After the one hour cool water is sprinkling every one hour for 5 minute and temperature is gradually decreases around the normal range (101-101.50 F) period of one and half hour. Animal is alert and start the feeding and rumination after 5-6 hour cooling therapy. After 5-6 hour giving the supportive and electrolyte therapy is very important in heat stroke patient and all the animals are treated with intravenous – inj. Intalyte1 500 ml, inj. Tribivet1 10 ml and per oral give Bolus.Rumentas1 2 boli, Bolus.Ecotas1 2 boli daily for 3 days, Polv. nutrimilk gold3 30gms and vitamix gold3 7ml daily for 30 days.
