B S Khadda, Kanak Lata, Raj Kumar, J K Jadav, S Khajuria and A K Rai
ICAR-Krishi Vigyan Kendra (CIAH), Panchmahal,
Godhra-Baroda Highway, Vejalpur-389 340 (Gujarat)
Corresponding author: B S Khadda, E-mail firstname.lastname@example.org
The environment can be defined as the combination of external conditions which have an impact on animals and humans. Perhaps the most important physiological response of poultry to the environment is the constant maintenance of a homoeothermic state during exposure to extreme ambient temperatures. Environmental stress causes adverse effects on performance of poultry. There are different types of stressors, namely:
- Climatic stress i.e. heat and cold stress.
- Managemental stress i.e. poor ventilation, excess light, wet litter, etc.
- Nutritional stress i.e. imbalanced ration and low nutrients.
- Physiological stress i.e. sexual maturity and rapid growth.
- Physical stress i.e. transportation, catching, injection, immobilization, etc.
- Social stress i.e. overcrowding, poor body weight.
- Psychological stress i.e. fear and harsh caretakers.
Among all these types of stressors, environmental stress adversely affects the production performance of commercial poultry. In general the ideal temperature under which chicken feels comfortable, functions normally and also for optimum poultry production is 65-80oF. Birds like mammals are homoeothermic which means they can maintain a relatively constant deep body temperature 41.7oC (107oF). After 101o F and above temperature is often referred to as lethal temperature and chicken possess into a state of shock culminating death.
The environment in which poultry is maintained is the single most important factor affecting productivity. The thermoregulatory mechanism in birds is effective only upon the ambient temperature within certain limits (18-28o C). Beyond this birds cannot adjust well. The upper lethal temperature in birds is about 47o C (116.8oF), this is called thermo neutral or zone of comfort during which birds do not change their behavior or signs of discomfort and use minimum amount of metabolic energy to maintain homoeothermic range of body temperature. Within the thermo neutral zone, body temperature is maintained by the thermal equation (heat production =heat loss).
MANAGEMENT OF CHICKS DURING SUMMER
Summer season causes number of deleterious effects on broilers and layers which ultimately reduces profitability. Summer stress a serious concern for poultry producers as it directly leads to financial losses by impaired poultry performance. Heat stress begins when the ambient temperature climbs above 80o F and is readily apparent above 85o F. When a bird begins to pant, physiological changes have already started within its body to dissipate excess heat. Even before the bird reaches this point anything that you do to help birds remain comfortable will help to maintain optimum growth rates, hatchability, egg size, egg-shell quality and egg production. During summer month when daily temperature regularly reaches 90o F, it becomes critical for the birds to dissipate body heat to the surrounding environment. Birds become heat stressed when they have difficulty in achieving balance between body heat loss and body heat production, the normal body temperature of poultry being 41°C (105.8o F). When environmental temperature exceeds 35o C bird is likely to experience heat stress. In an effect to maintain body temperature birds first rely on losing heat from blood vessels near surface of skin by process called non-evaporative cooling. However, this mechanism is only effective when ambient temperature is lower than bird’s body temperature. As ambient temperature increases beyond bird’s thermo neutral zone, non-evaporative cooling becomes ineffective. At these higher temperatures, bird relies on panting/ evaporative cooling as mechanism for controlling body temperature. Panting is an effective but energy expensive way for the bird to control body temperature and typically results in lower feed intake and growth as well as reduced feed efficiency between 20-30o C feed intakes is reduced by 1-1.5% for 1o C rise in temperature and by 5% above 32o C.
The will increase water intake to offset water loss but situation is complicated by the fact that body’s ability to retain water is reduced as the evaporative cooling process escalates. During high ambient temperatures, the birds increase panting up to 10 times from a normal rate of 25 breathes/ minute to 250 breathes/ minute.This leads to an excessive loss of carbon dioxide resulting in raised blood plasma bicarbonate levels and increased blood ph. The bird attempts to correct blood ph by excreting bicarbonates via urine. Bicarbonates are negatively charged ions that must be coupled with positively charged ions such as potassium to be excreted in urine. However, as potassium is important in maintain intracellular water balance, a loss of potassium ions via urine reduces ability to maintain this water balance. Consequently, while birds do compensate for water losses associated with panting by consuming more water, its retention in the body cells is limited by simultaneous loss of electrolytes such as potassium in urine.
EFFECT OF HEAT
Most important effect of heat stress is decrease in body resistance and more susceptibility to E.coli and CRD etc. In summer outbreaks of gout may be seen in broilers and layers. In heat stressed birds blood flow increases to upper respiratory tract, skin and abdominal muscles for relieving heat, however, blood flow to intestinal tract is decreased. As a result there is reduction in appetite leading to lower feed intake. Concurrently water intake is increased resulting in fluid contents in intestinal tract. This further cause’s diarrhea that results in loss of electrolytes needed to maintain acid base balance.
Symptoms of heat stressed:
The following signs will be observed in heat stressed birds:
- Rapid respiration / Panting
- Reduced appetite
- Reduction of egg production
- Poor egg shell quality
- More intake of water
- Reduced feed efficiency
- Less body weight gain in broilers
- Increase in body temperature
Steps to combat heat stress
The aim of adopting measures to combat heat stress is not only to keep birds alive but also to get production out of them to achieve targeted figures i.e. number of egg from layers and a better body weight at particular age with specific FCR in broilers.
Management practices which help to combat heat stress in birds:
- Housing Management
- Feed Management
- Water Management
- General Management
- Orient the long axis of poultry house should be east-west direction to minimize solar heating and direct access to sunlight.
- Poultry houses should have good roof insulation in arid and semi arid region (if possible with false roof to reduce the conduction of heat) with support of foggers and cooler systems.
- In open sided houses, width of house will be a limiting factor so keep the optimum width (24-32 ft) based on temperature, humidity and wind velocity, type of house and nature of bird for effective cross ventilation.
- Increased air movement over the birds by cooler fans/ exhaust to produce a wind chill effect which will cool birds even without drop in the house temperature.
- Shed design and construction should not allow direct sunlight on birds.
- Thatching of roof with straw will reduce temperature inside the shed.
- The roof should be painted with white wash to reflect sun light.
- Shades from tall trees and plantation around the sheds can reduce the radiant heat. The plantation of trees should be such that trees will be leafy during summer and bald during winter.
- Roof overhangs should be sufficient (3-5 ft) to protect the birds from strong sunrays.
- During summer season feed intake of birds is reduced considerably as results to reduced body weight, egg production and egg quality.
- Increase the frequency of feeding.
- Do not offer feed during day time in broilers.
- Certain changes in feed formulations are necessary.
- Increase nutrient density of feed to compensate for depressed feed intake.
- Energy level of feed should be reduced.
- Crude protein content should not be increased because heat generated by one gram of fat is 16.5% or one gram of protein is 22.5%.
- Similarly 25-30% extra vitamins and trace minerals should be added in the feed during summer season.
- Available phosphorus content of feed should be increased.
- Vitamin C is necessary to maintain integrity of blood vessels, so supplementation of vitamin C at the rate of 250-500 gm /ton feed will be beneficial.
- Vitamin E at the rate of 50-60 gm /ton feed will also be beneficial.
- Pelleted feed is beneficial where low energy fiber diets are used.
- Add soda-bicarbonate at the rate of 0.1% for improvement of shell quality of the eggs.
- The diet should be balanced with limiting amino-acids, methionine and lysine which will give better results.
- Increase the calcium level from 2.5-3.5% in layer diet.
- Addition of vitamin A 8000 IU and vitamin E 250 mg/ kg diet for better performance and combat heat stress.
Practically water is the most important criteria of these four managemental factors during summer. In summer water consumption is increased 3-4 times. Even a minor deficit of water can lead to heat stroke and mortality. Normally feed and water consumption ratio is 1: 2 but when temperature shoots beyond 95oF, this ratio may increase up to 1: 4 or more. The following points to be taken into consideration:
- Supply of plenty of clean and cool water (60-70oF) must be ensured during summer season.
- Use good quality sanitizers in water to control infections through water.
- For day old chicksprovide cool water and electrolytes on their arrival to farm before offering feed to avoid dehydration after transportation.
- Cover water tanks with wet gunny bags to avoid direct exposure to sun.
- Increase number of waterers by 25%.
- Increase frequency of watering.
- In case of nipple drinkers, insulate nipple pipe with wet gunny cloth.
- Provide electrolyte (1-2 gm/liter) in water during hot hours.
- Addition of 0.25% of salt to drinking water increases water consumption.
- Adjust the amounts of medications and volumes of water used for water vaccinationto reflect the increase water consumption of the flock during hot weather.
- Do not withhold drinking water from the flock when vaccine is provided through drinking water.
- Cover water tanks with wet gunny bags to avoid direct exposure to sun heat.
- Litter preferably fresh litter of 2 inches thickness with racking or stirring of litter 2-3 times a day during cool hours is recommended.
- 10-15% extra floor space should be provided during summer season.
- Overcrowding of birds should be avoided.
- Shifting, transportation, de-beaking and vaccination should be done during night or cool hours of the day.
- Birds severely heat stressed may be dipped in cold water for 2-3 minutes keeping their neck and head above water level.
- Proper cross ventilation should be providing.
- Fans (pedestal, ceiling or exhaust) may be fitted in sheds.
- Use foggers in the shed which could reduce the shed temperature up to 5-10oC depending upon quality.
- Use of white paint ,white lime, etc practically reduces the shed temperature up to 2-5oC
- Use side curtain in shed which should be sprinkled with water.
- Provide 3 exhaust fans on one side and pad cooling on other side (200 ft) which completely seals the shed sides and brings down temperature below 8-10o
- Use sprinklers on the top or inside shed.
- Thatched roof is suitable for hot areas.
- The house should be situated away from other buildings in order to facilitate free movement of air.
- High altitude of roof is ordinarily 2.6 to 3.3 m from foundation to the roof line to provide maximum ventilation.
- Provide 1-1.25 meter overhang to cut the direct sun and rain into the house.