By – Dr Surinder Khanna, Poultry Consultant
Open mouth panting is a sure sign of heat stress
The signs of heat stress are open mouth panting, wing spreading,
and squatting close to the ground. By adjusting the position of their
feathers, the birds are trying to lose heat. By gasping they are losing
water in their breath and cooling themselves by evaporation from the
surface of the lungs.
At an environmental temperature of 28°C (82°F) appetite is depressed
by 12% and where high rela¬tive humidity is also present, by as much
as 50%.
Visible signs of heat stress in poultry
In general, birds will be suffering heat stress when any of the following signs are evident:
Gasping, panting, panting respiration – up to 250 breaths per minute – mediating evaporative cooling from the surface of the lungs (80% of heat is lost this way)
wings spreading
Stupor, staggers and terminal convulsions.
Slowness and lethargy.
Increased cannibalism
More Carcass down grades.
Light body weight, poor colouring and rough skin.
Egg production drop for no apparent reason
Reduced egg size, poorer egg shell quality
Increased mortality
Increased output of urine – further loss of electrolytes
Wet droppings develop
Thirst increases- many times
Bone metabolism is disturbed e.g. tibial dyschondroplasia
Ascites incidence increases
Immunity to intercurrent disease is lowered
Appetite is depressed, there is some indigestibility of feed
and gut motility is slowed. Nutrient deficiencies may occur.
There is loss of body weight
Downgrading of over-fat carcasses
Fertility is lowered
Growth and growth rate are depressed
Replacement pullets are lighter, lay later and lay fewer eggs
Egg weight decreases
Egg downgrades increase
The absorption of minerals is altered
Birds grow unevenly
Force feeding for higher consumption levels leads to greater
mortality.
In Breeders, reduced fertility, due to less mating, poorer semen
quality and female infertility
Invisible signs of heat stress in poultry
ph of blood plasma rises
pH within the cells falls
Urine output increases and so does electrolytes
Bicarbonate (HCO3) is lost
Stress hormones appear in the blood
Gene function is disturbed
Resources being diverted to unproductive efforts by the
animal (bird) to restore balance (homeostasis)
Heat shock proteins are activated to shut down metabolic
reactions and to protect heat-sensitive tissues.
Responses to intercurrent diseases or pathogens decline rapidly.
All production is stopped due to loss of homeostasis
Water alone is not enough
Learn how birds regulate their deep body temperature
It is not enough to give the bird water alone. This only increases the problem, by further stimulating the loss of electrolytes. When birds are sick or stressed, they have a higher body temper¬ature. (For every 1°C rise in body temperature, metabolism increases 20-30%.) Birds drink more, respiration rate increases, pulse rate falls and the amount of wet droppings increases. Diarrhoea hastens dehydration.
Clinical signs at post-mortem of poultry suffering from heat stress
Broiler and layer chickens produced in tropical climates struggle to
perform in high temperature and humidity conditions. These birds
display external signs of heat stress; including open mouthed breathing,
wing spreading, performance loss and sometimes mortality. With these obvious signs of heat stress come less obvious signs such as deep body temperature increase and the biochemical and physiological changes that take place as a result.
When deep body temperature is elevated for prolonged periods,
biochemical and physiological changes damage vital body organs such as the heart,lung, liver and kidney.
At post-mortem obvious signs of organ damage present with
the following characteristics:
The heart muscle increases in size at the right atrium with
significant blood accumulation. Lesions are often present.
Congestion and build up of fluids and blood is common. Lesions
are often present.
Colour changes to a pale yellow and is congested. Lesions are
often present.
Kidney
Swells and is inflamed, water blood and urine accumulates.
Other obvious signs at post mortem:
Muscles are dry and sticky to touch.
Blood is thicker and darker than normal.
Crop and gizzard are empty and dry. Gizzard
lin¬ing peels off easily.
The above clinical signs emphasize the need for poultry producers
to do everything possible to minimize the increase in deep body
temperature .
Nutritional changes in the feed along with change in management practices can minimize the heat stress losses in summers.
1. Energy: – Energy intake is one of the most important factors during summer season. Because of higher climate temperature, bird needs lesser energy by 30 kcal per day but on the same time bird wants energy to dissipate body heat so net energy requirement is almost same. But as the shed temperature keeps on increasing the fed intake goes down.With each one-degree Celsius rise in temp, the feed intake fall by almost 2% and at 39 to 40 degree Celsius it falls by 5%, so this is the time farmer can add some oil in feed to increase feed density. As the oil have lesser heat increment & also feedstuff passes slowly through gut, so more nutrients can be absorbed. Oil also increases the palatability of feeds that can lead to increase in feed intake to some extent.( dose: 0.5 to 1% can be added ).
2. Proteins: – Giving a high level of protein at a very high temperature can lead to heat prostration because heat increment of proteins is much more than carbohydrates and fats. So bird has to dissipate more body heat, which can lead to heat stoke. Maintaining ideal levels of essential amino acids (lysine & methonine) rather than increasing protein level is a much better option though.
3. Calcium, Phosphorous: – High level of calcium in feed also reduce feed intake so optimum level of calcium is required. However top dressing of marble chips or shell grit during afternoon can be done to meet calcium requirement. The phosphorous levels in feed is also very important.Excessive level inhibits the release of bone calcium & the formation of calcium bicarbonate in shell gland thereby reducing the shell quality.
4. Vitamins: – Additional supplementation of ascorbic acids (vitamin c), vitamin A, E, d3 & thiamine can improve bird’s performance during high shed temperatures. However, vitamins have a tendency to loose their activity at high shed conditions . Rancid fats, moisture, trace minerals & choline speeds up the devaluation of vitamins, so should be added separately or coated vitamins should be used along with proper storage. Vitamin C helps to control the body temperature & Plasma corticosterone concentration hence decreases stress level of birds. It also improves shell quality due to role of formation shell organic matrix. It also protects immune system. Additional supplementation of 200 – 600 Gms per kg diet is required during hot climate.
• Vitamin A: – absorption at high temp. goes down so three fold vitamin supplementation can be given.
• Vitamin E: – It protects cell membranes & boost immune response so additional dietary supplementation is required.
• Vitamin D3:- Heat stress interferes with conversion of vitamin D3 to metabolic active form which in turn is responsible for production of calcium binding proteins & also essential for calcium & phosphorous homeostasis’s
Techniques to reduce losses during hot climates
1. Water dropping system on side curtains can be installed to reduce the temperature of hot air across the shed. Once the air temperature goes down, birds will dissipate more heat from the body & chances of heat prostration will reduce.
2. Fans along with the foggers can be installed to increase the airflow inside sheds particularly in hot & humid climates. Fans should also be kept switched on during night hours so that bird loose extra body heat & get ready for the next day challenge.
3. A layer of Thatch or Zinc paint can be provided on the roof to avoid heating of roof.
4. Fresh & cool water should be provided particularly during hot hours of daytime.
5. Feeding during hot hours should be avoided because that will lead to production of heat in the body hence heat prostration will occur. So feeding during morning & evening time is suggested.
6. Grass can be cultivated in between the sheds to reduce reflection of radiations.
Advice for the upcoming Farmers
As the land price are very high these days particularly, people trying to have a maximum laying capacity in a given area compromising with the comfort level of the birds.
As a new farms with four row sheds, six to seven birds per cage are coming, the comfort level of the bird is compromised in terms of lesser feed space and more number of birds per unit area. Sheds with 4-5 birds per cage are much better in this regard.
The height of the sheds particularly in four row sheds should not be less than 12feet. Also the gap between the two rows should not be less than 4.5 ft to 5 ft. The gap in-between the sheds should not be less than 55 to 60 ft.
In these types of sheds bird remain much comfortable because of following reasons.
1. Lesser number of birds per unit area will have low temperature of the shed.
2. Effect of heat radiation generated by heated building sheds during hot climate will be much lesser. Suspactibilty to diseases also decreases.
