by Dr. Tara Nath Gaire
Department of Veterinary Medicine and Public Health
Institute of Agriculture and Animal Science (IAAS), Rampur, Chitwan, Nepal.
Chickens may acclimatize to hot temperatures (30 – 35 degrees Celsius) over a period of 5 days but become vulnerable to very high temperatures because they are unable to adjust to very hot weather (35-45 degrees Celsius) that appears suddenly. A heat stress prevention strategy is therefore needed before, during and after these very hot days if losses are to be avoided.
Signs and Symptoms
Appetite is depressed – water consumption rises.
Heat is lost by increasing the evaporation of water from the wings, air sacs and bronchial tree – and to a lesser extent, the skin.
- Respiration rates increase even beyond 250 breaths/minutes in severe Heat Stress and panting and gasping is quite common.
Activities are usually shifted to early morning or early evening.
Effect of Temperature and relative humidity on poultry
| Temperature | Relative humidity | Effect on living conditions of poultry | |
| F | C | ||
| 68 to 78 F | 20 to 26 C | Up to 40% | Optimum |
| 78 to 86 F | 26 to 30 C | 40 – 75% | Harsh |
| 86 to 104 F | 30 to 40 C | Up to 45% | Progressively extreme |
| 86 to 104F | 30 to 40 C | 65% and above | Impossible |
Diagnosis
In heat stress, intracellular calcium concentration increases which gives rise to efflux of Creatininekinase from cells to plasma. Elevation of plasma creatinine kinase is indicator of heat stress in chickens. But routinely laboratory tests are not necessary to diagnose heat stress condition.
PM Changes
In dead birds autolytic changes set in fast and in the post mortem examination of fresh carcasses, engorgement of subcutaneous capillaries, congestion of abdominal and breast muscles(cooked meat appearance), congestion of trachea, combs and wattles may be seen.
General Recommendations Concerning Heat Stress
- Under normal conditions, birds should be fed so as to attain optimum daily intakes of essential nutrients.
- Ventilation
- Installation of evaporative cooling system on farms
Daily management
Feed withdrawal from 9am to 4.30 pm.: This is very effective in reducing heat stress mortality. Feed intake and digestion produce nearly 7% additional heat in the body which is maximum 4 to 5 hours after feed intake. This should not coincide with hottest part of the day (2 to 3 pm) Birds fasted in the day compensate intake in the night time and it should be seen that lights do not go off in night.
If biosecurity is poor, feed withdrawal may lead to coccidiosis, necrotic enteritis. Necessary medicines may be kept at hand in case such eventuality arises.
Drinking Water: Cool Water (at 10-12 C) should be supplied continuously to birds. Watering space should be doubled.
a) In moderate hot weather
Ascorbic acid….62.5 mg/litre
+ Acetylsalicylic acid 62.5 mg/litre
+ Sodium bi carbonate 75 mg/litre
+ Potassium chloride ( KCl) 125 mg/Litre
b) In heat stress
Vit C 400 mg/ L
+ Electrolytes
+ Acetyl salicylic acid ( Disprin 1 tablet/5 L)
+ Sodium bicarbonate 1gr/Litre
Feed Formula
Increase the energy level of the diet (2850 Kcal ME/kg minimum) ideally by incorporation of fats or oils. Limit the use of fibrous ingredients if possible.
Reduce crude protein component (17% CP maximum) while maintaining daily intakes of methionine (360 mg) and lysine (720mg).
Increase mineral-vitamin premix in accord with anticipated change in feed intake. Maintain daily intakes of calcium (3.5g) and available phosphorus (400 mg).
Vitamin C: Because of the release of corticosteroids in heat stress, there is increased demand for Vit C by adrenal glands for controlled production of hormones needed for gluconeogenesis. In heat stress there is also reduced synthesis and partial depletion of Vit C. Inclusion of Vit C at 150 – 200-400 g/ton of feed is recommended in summer months. If included in feed , there is no need to give ;in water again.
Anti oxidants: In heat stress there is excessive oxidative metabolism and release of free radicals in the body. Free radicals damage all types of biological molecules, and cells of vital organs more so of immune system VitE captures and neutralizes free radicals and its inclusion at 50 to 100 ppm in feed is advisable. Vitamin C also has antioxidant property.
Toxin binders: In wet summer, there is rapid growth and toxin formation in feed. Good quality toxn binders at higher dose should be used in feed.
Vaccination: Strict cold chain should be maintained during transport storage and administration of vaccines. Vaccination should be carried out during cool hours. Immunostimulants should be given for three days following each vaccination.
Summary
Summer is a challenging season to poultry farming.There is no single solution to hot weather problems and series of measures are necessary to minimize losses due to heat stress.
