General Beven Mundida
This article evaluates some of the effects of heat stress on birds, and suggests ways by which poultry producer can help to alleviate some of the detrimental effects of heat stress on their birds and as such improve the birds’ productivity.
What is Heat Stress- Heat stress is a condition that occurs when the body’s means of regulating either the external (environmental) or the internal (within the body) heat fails and the body temperature rises to critical levels leading to other medical conditions such as heat exhaustion or heat stroke. Heat exhaustion is a result of the combination of excessive heat and dehydration. Heat stress is a common cause of death in birds especially broilers. It also predisposes layers to low productivity. It is mostly seen during the hot season and dry season especially when the population of the birds exceeds the capacity of the pen or cage size. During this period, the chickens have to make major thermo-regulatory adaptations while the farmers also need to make some adjustments in management practices to help the birds overcome this condition.
Factors that predispose to heat stress – Heat is essentially produced by the activities that go on within the body (metabolism) which is used for maintenance, growth and egg production. Heat production is influenced by body weight, species, breed, level of production, amount of feed intake, feed quality and in some cases, the level of activity and exercise. Also if the stocking density is too high for the size and design of poultry pen or house, the temperature will rise significantly. There will be more metabolic heat being added to the hot air within the pen. Radiant transfer from bird to bird is greater increased and stagnant hot air is trapped between the birds. The heat (hot air) within the pen is an accumulation of metabolic (body) heat, added to the air of a building, heat from electric lights, heat from the roof and walls, and heat from the fermentation of the litter or accumulated droppings. Of these, the dominant source of heat is body heat. Fermentation of litter is usually at least equaled by the heat absorbed in evaporating litter moisture. The heat of electric lights and other heat-generating devices such as electric motors is a very small fraction of that produced by body metabolism (normally less than 1%). However, radiated heat coming from a poorly insulated roof can make heat stress worse in hot weather. Some natural characteristics of birds that affect heat loss to the environment include; their feather cover, size of their combs and wattles and the posture in which they assume.
Indicators of heat stress – Change in room temperature or body temperature of the birds: can be measured with a thermometer and it is the simplest method of detection of thermal strain on birds as side other clinical signs that the birds show. The body temperature of a hen varies between 40 and 42°C, depending on the time of day (before and after feeding, night time), feather cover (in connection with moulting), brooding, and environmental temperature. The ideal environmental temperature for chickens is 18-24°C. However, if the temperatures exceed 24°C, the bird uses 4 possible ways to release this excessive body heat ie. radiation, conduction, evaporation, and convection. The main indicator of heat stress in chicken is continuous/prolonged panting, gasping and dropped wings. If this is not rectified, it will lead to the collapse and death of the birds. Other clinical signs include; wet dropping, slowness, lethargy, increased water intake, reduced feed consumption, reduced egg production, poor colouring, rough skin, and cyanotic combs and wattle.
Tips on handling heat stress
1. Avoid overcrowding: Heat loss often depends on the difference between the body temperature of birds and the ambient temperature. If stocking density is high, the radiant heat between the birds accumulates and the temperature increases. Therefore, birds cannot lose body temperature.
2. Avoid unnecessary bird handling: Any form of stress on the birds especially during the hotter periods of the day should be avoided. Vaccination, transfer, beak trimming, or any other kind of handling should be done in the early hours of the morning or after the sunset at night. Moreover, handle the birds as calmly and gently as possible.
3. Provide cold water in hot weather: Ensure sure that there is constant water available for the birds more preferably chilled when the weather is hot.
4. Supplement drinking water with electrolytes: When chickens pants, it alters their electrolytes, so adding electrolytes helps re-balance them. It also increases the water intake by the birds, and the more water they drink the better for them.
5. Feeding at cool periods of the day: During the heat of the day chickens tend to eat less, so it is preferable that you feed the chickens during the early hours of the morning and cool hour of the evening because digestion naturally increased body heat generation.
6. Install fans and other cooling systems: A misting or fogging system or a normal fan helps lower the temperature within the pen and that of the chicken body. It sprinkles water on the chickens’ bodies and helps to cool them.
7. Keep chickens in a well-ventilated area with adequate airflow: The design and construction of the pens or poultry house should be in such a way that it is well ventilated. Accessory windows and sufficient routes of aeration of the pen or house is created in case of emergencies. That could encourage natural ventilation or compliment the fans or the cooling system.
8. Provision of well-insulated ceilings: This helps to reduce the intensity and effect of heat directly from the sun and roof into the pen and on the birds.
9. Regular changing of litter: The litter should be changed regularly and properly dispose to prevent accumulation and decomposition of the litter which and heat generation by this process. Removal also keeps pests to a minimum.
10. Install emergency temperature alarm systems and generators: This helps to detect an increase in temperature within the poultry house and in turn, automatically switches on the cooling system. The generators, on the other hand, should be kept on standby in case of electricity failure.
Poultry farmers are therefore saddled with the responsibility of helping their chickens survive the effects of heat stress. Through guided and careful approaches mentioned.
Contact General Beven Mundida (Animal Production Specialist) for more information, +263776420161 +263715009507
Photographs provided by General Beven Mundida
First published on ZiMunda Farming Magazine issue 3.