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Ian Cockshott, Technical Service Manager for Ross in the Middle East & Africa looks at practical ways to manage stock in hot weather
Extremely high temperatures have a much greater effect on the faster growing, higher yielding broiler of today than its less efficient ancestors. When it's hot outside, it is essential to create an environment inside the poultry house that allows the birds to dissipate excess body heat and remain comfortable. Recent advances in housing design have greatly improved our ability to create a good environment inside the poultry house, providing the opportunity to maximise poultry performance in hot climates. In such high temperature climates, secondary issues to the environmental conditions are those such as the presence of insect vectors, bacteria and mycotoxins. In these challenging conditions it is essential that key management techniques are applied in order to gain maximum performance of stock.
In the extremes of the Middle East climate, ambient temperatures can range from anything between -10ºC to 55ºC during the year and the diurnal temperature range (the difference between that during the day and that during the night) can be 20ºC. Relative humidity, which will affect the apparent temperature the birds feel, can range from 10% inland, to 90% by the sea.
Bird Biology in Relation to Temperature
The chicken's body temperature is approximately 41ºC, although this rises slightly during the day and falls slightly during the night. The bird maintains it by employing sensible heat loss methods i.e. heat loss from the body to environment by radiation, convection and conduction and also to some extent by water evaporation from the skin or latent heat loss. These methods must be equal to the heat produced within the body as a result of digestion, absorption and metabolism of feed, so that the bird balances energy and heat production to maintain body temperature.
An important mechanism in the process of heat regulation is the control of blood flow to the peripheral tissues, especially the comb, wattles and legs. When the bird needs to lose heat, blood flow to these parts increases and it warms up. This process, known as peripheral vasodilatation, moves heat from deep inside the body to the surface, to be lost to the surrounding environment.
The Effect of Heat Stress
As environmental temperature rises, a change in behaviour of the birds will become evident. Key points to note are: wings being held away from the body to assist heat loss from the unfeathered areas on the underside of the body; reduced activity to limit heat production from muscular efforts; an increase in water consumption and a decrease in feed intake.
About 75% of the metabolisable energy consumed by the bird will be converted to body heat and require to be lost to the environment. Thus reduction in feed intake is an important physiological safety mechanism to reduce heat stress.
As temperatures rise, the ability to lose heat by conduction, convection and radiation decreases. At this point, the bird will then try to loose heat by panting, which assists the evaporation of water from the moist linings of the respiratory system. This evaporative cooling initially involves the process of passing air rapidly in and out of the mouth and is the principal means of regulating body temperature in heat stress. However, at higher temperatures water also evaporates from the air sacs within the lungs during panting, lowering the levels of blood carbon dioxide and inducing a process called respiratory alkalosis. This condition can have a serious impact on broiler performance particularly when accompanied by decreased feed intake, due to the decreased potassium and minerals balance.
In general, birds with higher metabolic loads e.g. male broilers and laying birds will be more sensitive to heat stress. When heat production exceeds the bird's ability to dissipate heat, birds will lie prostrate and gasping on the floor, which results in them becoming more weak and susceptible to dying from respiratory, circulatory and/or metabolic imbalance.
Managing the Poultry House Environment
Ensuring a good environment inside the poultry house and providing the opportunity for birds to dissipate excess body heat and remain comfortable can be accomplished by keeping ambient temperatures in the poultry house at recommended levels. If this is not possible, an alternative approach is to increase the speed of the air flowing over birds to accelerate body heat dissipation and the loss of heat by convection.
This accelerated heat dispersal from birds, otherwise known as wind-chill cooling, can be accomplished using tunnel ventilation and makes the birds feel that they are in a cooler environment. This is particularly important at higher humidity levels when the effectiveness of evaporative heat loss, which occurs when birds pant, is reduced. At higher relative humidity, increasing the air flow over the birds promotes heat loss by convection.
The litter is a significant source of moisture and so should be managed carefully to maintain relative humidity levels in the poultry house of no more than 70%.
There is some evidence that by acclimatizing birds at an early age they are more capable of surviving a heat stress later on.
No direct sunlight should penetrate into the floor space of the house and outside the shed the area should be kept clear for up to 3 metres to prevent restriction of the airflow into the shed.
Bird Management and Nutrition
One of the key factors to consider is stocking density. Reducing the stocking density reduces the number of birds producing heat and so reduces the amount of heat that must be removed form the house to maintain temperature. Future hot weather can be anticipated and placement numbers should be planned accordingly, taking into account the likely outside temperature and humidity, the type of housing, the capacity of the ventilation system and the type of stock housed.
Table 1: Recommendations for house type and stocking density for Broilers
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House Type
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MAX Stocking Density at Slaughter(Kg/m2)
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Closed
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30
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Closed hottest time of the year
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24-26
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Open - Sided (OS)
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20-25
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OS hottest time of the year
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16-18
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Water Management and Supplements
Water consumption increases during hot weather and so an adequate supply of cool, fresh water should be available to birds at all times. As an approximate guide, water consumption increases by 6% for every 1ºC rise in temperature from that at 20ºC where it is approximately 1.8 - 2.0 times feed quantity. Care should be taken to ensure drinkers are working properly and that there is enough space to allow birds free access.
The addition of 8g per 100 litres of sodium bicarbonate to the drinking water (or 25g/kg in the feed) can be useful in heat stressed broilers to stimulate water consumption.
Fortification of water with vitamins and electrolytes is also prudent especially in circumstances where feed intakes are low due to the effects of hot weather.
Feed Specification
Increasing nutrient intake during heat stress, by changing the feed specification, may have an adverse affect on survivability, but increasing the digestibility of nutrients and the use of specialist micro ingredients has been shown to have benefits.
The principle nutrients to consider are;
- Proteins and amino acids: nutrient digestibility should be increased rather than nutrient density, minimize excess protein and balance amino acids and minimize the crude protein level in the diet.
- Energy: the diet should be supplemented with fat rather than carbohydrate. Increasing the energy density of the diet will increase growth rate but will also increase heat output.
- Vitamins and Minerals: certain vitamins are known to have a positive effect on the birds' response to heat stress including Vitamin E, D, A, C, B2 and nicotinic acid. Under no circumstances should vitamins be withdrawn from the diet.
Feeding Management
As temperatures rise, the bird has to maintain the balance between heat production and heat loss, and so will reduce its feed intake. Trials indicate that feed intake is reduced by 5% for every 1ºC rise in temperature between 32-38ºC.
Reduced feed intake is the main cause of poor performance at high temperatures and the feeding practises below have been shown to have a positive affect on survivability and performance of birds experiencing heat stress:
- Ensure good physical quality of feed (crumb, pellets or mash) to encourage appetite. If floor space allows add extra feeders.
- Feed should not be stored for longer than one week to reduce the possibility of mycotoxin build up.
- Encourage eating at cooler times of the day as it takes 2-4 hours after feeding before the maximum energy is generated and the bird must dissipate the metabolic heat generated.
- Remove feed 4 to 6 hours prior to an anticipated heat stress period. Birds should not be fed or disturbed during the hottest part of the day.
- Dim the lights while feeding - low light intensity during periodic feeding reduces activity which reduces heat load.
Other Points for Breeder Flocks
- Try to plan flock placements to avoid peak production at the time of the greatest heat challenge.
- Monitor eating up times and record them on a daily basis.
- Stressful procedures such as beak trimming and grading should be delayed until the weather cools off.
- Males with a full comb will be much more capable of losing heat than those without.
- Reduced feed intake can increase susceptibility to calcium tetany. To ensure adequate calcium is available for eggshell production, feed oyster shell grit as a scratch feed. If feed intake is reduced by 20g per bird per day, then calcium intake falls by approximately 0.56g. Feeding 1.5g of oyster shell grit per bird will replace this.
Other Points for Broiler Flocks
- Sexed growing allows separate ventilation of slower feathering and faster growing males.
- A lower daily feed intake (80%-90%) is compensated for by a longer growing period.
- Frequent feeding and stirring of feed in the feeder should be encouraged to stimulate intake.
- Intermittent lighting programmes can be helpful in closed housing. Studies have shown improved growth performance and immune response with a continuous 1 hour light and 3 hours darkness intermittent programme.
- Depletion should be well organized and slower than usual. Water should be available until the last birds have been depleted and feed withdrawal should occur 2-6 hours before depletion. Efforts should be made to avoid moving birds in the hottest part of the day and to eliminate waiting at the factory.
Summary
Good management practice plays an important role in minimizing the effects of heat stress in hot weather. Advance planning of flock placement and good management practices can significantly reduce the impact of high temperatures. The advice given here will help to maximize the dissipation of heat produced by the bird in such an environment, while minimizing any negative impact on biological performance.
Courtesy of Poultry Middle East & North Africa, March/April 2004
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