Vetcare Update bulletin - Management in Summer Stress

Chickens, unlike most other animals, do not possess sweat glands to aid in heat loss. The chicken removes excess body heat in four ways. Body heat can be lost by radiation from the skin surface through thr air to another object (i.e., another bird). Heat can be directly transferred by conduction to cooler objects with which the bird is in contact, such as the cage, litter, or slats. Body heat is also lost to b surounding air by convection. When the environmental temperatures are between 28⁰C and 35⁰C (82⁰F and 95⁰F), radiation, conduction, and convection heat losses are usually adequate to maintain the bird's body temperature. The bird dilates the blood vessels of the skin, sattles and comb to bring the internal body head to the skin surface to facilitate conductive and radiation heat loss. Floor birds will search for cool places in the house and dig into the litter to increase the conductive and convective heat loss. Drooping of the wings promotes convective heat loss by increasing heat stress because they are unable to seek a cooler place and thee is less conductive heat loss in cages. As the environmental temperature approaches the body temperature of the bird, 41⁰C (106⁰F), the efficiency of these heat loss mechanisms diminish. At this point the evaporation of water from the respiratory tract becomes the major heat loss mechanism of the bird. The evaporation of one gram of water dissipates 540 calories of maintenance energy. Birds pant (open mount breathing), or hyperventilate to increase evaporative cooling. When panting fails to prevent the rise in body temperature the bird becomes listless, then comatose, and soon dies. Birds raised from young aga at high environmental temperatures will acclimate to higher environmental temperatures and can maintain good productivity. The non-acclimated flock exposed to rapid increases in environmental temperature (acute heat stress) typically has the greatest loss in production and mortality.

Heat-stressed flocks usually experience a loss in appetite. This decreased feed intake can be compensated by formulating a more concentrated feed. The actual energy requirement of the bird is reduced at high environmental temperatures because the bird derives more of its required energy from the environment. All the other dietary nutrients (i.e., protein, minerals, and vitamins) remain the same, except possibly for phosphorus (which is increased). The following feeding changes during periods of increased temperatures are generally regarded as appropriate.

Under hot and humid conditions, feed should not be stored for longer than a week. The bird's body temperature increases after feed ingestion due to the thermogenic processes of digestion and metabolism. With morning feeding, the thermogenic effect coincides with the rising environmental temperature, aggravating heat stress, The thermogenic effect lasts for 8-10 hours at 35⁰C, compared to just 2 hours at 20⁰C. Metabolic heat production is 20-70% less in starved birds than in fed birds. Therefore, during hot weather, birds should be deprived of feed while the temperature is reaching and at its peak. Feeding during early and late hours of the day will help to minimize growth checks and mortality in broilers. Intermittent feeding, i.e. providing the light for 30 minutes followed by 3 hours dark, may also reduce the activity (heat production) of the bird but 20-30% more feeder and waterier space will be required. For layers, feeding during later part of the day will ensure sufficient calcium is available for optimum shell calcification,

Low feed intake is the main cause of poor performance at high temperatures. The following practices can help to raise feed consumption and may be worthwhile considering:

Energy intake is the most important nutrient limiting bird performance at high temperatures. The energy requirement for maintenance decreases by about 30kcal/day with increase in environmental temperature above 210C. Although the energy requirement for maintenance is lower at higher temperatures, most of the energy is wasted in heat dissipation, so the absolute energy requirement is not affected by heat stress.

The feed energy concentration should be adjusted to allow for the reduction in feed intake at higher temperatures. Feed intake changes about 1.72% for every 1⁰C variation in ambient temperature between 18 and 32⁰C. However, the decline is much faster (5% for each 10C) when the temperature rises to 32-380C. Measures to increase feed intake include the inclusion of fat in the diet. Feed consumption increased up to 17% by 5% fat supplementation in heat stressed birds because fat improves palatability. In addition, fat offers an extra calorific value by decreasing the rate of passage of digest, thereby increasing the utilization of nutrients.

Fats or oils with more saturated fatty acids are preferred in hot humid climates. The concentration of energy should be increased by 10% during heat stress, whilst the concentration of other nutrients should be increased by 25%.

The requirements for protein and amino acids are independent of environmental temperature so heat stress does not affect bird performance as long as the protein requirement is met. However, heat stress reduces feed intake and the levels of protein/amino acids need to be increased with the environmental temperature up to 30⁰C. At even higher temperatures, heat stress has a direct effect on production and there is no benefit in raising the protein level.

The correct amino acid balance in the diet minimizes fat deposition in the liver, thereby increasing the survival of birds under heat stress. So, a low protein diet with balanced critical amino acids (methionine and lysine) is more beneficial than a diet high in total protein during hot periods. The oxidation of excess protein or amino acids generates metabolic heat.

Heat stress reduces calcium intake and the conversion of Vitamin D₃ to its metabolically active form, 1,25(OH)2D3 , which is essential for the absorption and utilization of calcium. In effect, the calcium requirement of layers, particularly older birds, is increased at high environmental temperatures. To overcome this effect, extra calcium should be provided at the rate of 1g/bird in the summer months in the form of oyster shell grit or limestone. Supplementation should be made over the normal dietary calcium level (3.75g/bird/d) recommended for layers.

However, excessive levels of calcium reduce feed intake due to the physiological limit of calcium appetite and also reduced palatability Instead of increasing the diet specification, the calcium should be offered separately as a choice feed. Better results are obtained by offering the calcium source in the afternoon. The optimum particle size is the one that supplies the required calcium at the of time of shell formation. The minimum size to improve gizzard retention is about 1mm.

The phosphorus level in diet must not be forgotten as excessive phosphorus inhibits the release of bone calcium and the formation of calcium carbonate in shell gland, thereby reducing the shell quality.

Additional allowances of ascorbic acid (vitamin C), vitamins A, E, and D₃ and thiamine can improve bird performance at higher temperatures. However, the loss of vitamin activity either in premix or in feed during storage particularly at elevated environmental temperature is a prime concern and probably explains the conflicting results on the effects of vitamin supplementation during heat stress. High temperature, moisture, rancid fats, trace minerals and choline speed up the denaturation of vitamins. Vitamin activity in feeds can be maintained by using feed antioxidants, gelatin encapsulated vitamins, appropriate storing conditions and adding choline and trace minerals separately from other vitamins.

Ascorbic acid synthesis is decreased at elevated environmental temperature, making it an essential dietary supplement during the summer. The vitamin helps to control the increase in body temperature and plasma corticosterone concentration. It also improves eggshell quality via its role in the formation of the shell's organic matrix. Furthermore, it protects the immune system and reduces mortality in growing birds infected with IBD in a hot environment by protecting the lymphoid organs and thyroid activity. Supplementation of ascorbic acid (200-600mg/kg diet) improves growth, egg production, number of hatching eggs, feed efficiency, egg weight, shell quality and livability during heat stress.

The absorption of vitamin A declines at high temperatures. In broiler breeders, a three fold increase in supplementation has been found to be beneficial.

Vitamin E protects the cell membrane and boosts the immune system so additional dietary supplementation may be advantageous during hot weather. Mortality due to E. coli infection reduced significantly by supplementation of vitamin E in diet.

Heat stress is known to interfere with the conversion of vitamin D₃ to its metabolically active form, i.e. 1,25(OH)2D₃, so higher dietary levels maybe justified during periods of high temperature. The active form of vitamin D₃ is involved in the synthesis of calcium binding protein, essential for calcium and phosphorus homeostasis.

A number of compounds are effective in reducing the ill effects associated with hyperthermia although their cost may be prohibitive. Antipyretic compounds, e.g. salicylic acid and aspirin, minimize the levels of catecholamine in the blood during heat stress. The performance of heat stressed birds can be increased with magnesium aspartate, zinc Sulphate, diazepam, metyrapone or clonidine in the feed. Aureomycin has been found to alleviate the stress (growth depression) caused by injection of foreign protein or salmonella end toxin but it has not always been found to be beneficial. Acetylsalicylic acid (3% of the diet) increased me weight gain and shell quality in some reports but the effects are inconsistent. Resin pine, an alkaloid from the Rawolfia plant is known to prevent the loss of carbon dioxide from birds subjected to high environmental temperature, thus stabilizing the blood acid base balance. Flunixin, an anti inflammatory analgesic drug at 0.28 - 2.2mg/kg bodyweight per day increased water consumption by 150 - 300ml/bird/day . The anti-coccidial compound, nicarbazine (at the standard dose of 125mg/kg), has increased the mortality of broilers up to 90% during heat stress. Adding potassium chloride in drinking water can ameliorate the toxic effects.

Supplementing the diet with 0.5% sodium bicarbonate or 0.3-1.0% ammonium chloride or sodium zeolites can alleviate the alkalosis caused by heat stress. Sodium bicarbonate stimulates feed and .water intake at high environmental temperature. The body weight gain can be increased up to 9% by addition of these chemicals in the feed of heat-stressed broilers.

The excretion of potassium through urine is significantly higher at 35⁰C than at 24⁰C. The potassium requirement increases from 0.4-0.6% with a rise in temperature from 25 to 38⁰C. Each bird for maximum weight gain under hot conditions needs a daily potassium intake of 1.8-2.3g potassium .

To compensate for the reduced feed intake under heat stress, dietary allowances for electrolytes (sodium, potassium and chloride) may be increased by 1.5% for each 1⁰C rise in temperature above 20⁰C. Electrolytes are also present in the drinking water and these levels need to be taken into consideration. Excess intake of electrolytes can lead to wet droppings, Potassium chloride can be added to the drinking water (to give 0.24-0.30% K) but care must be taken to avoid imbalances. Excess chloride is known to decrease the blood bicarbonate concentration.

In emergency situations the flock can be sprayed with cool water to save the birds' lives. Comatose birds are rarely saved.
Check and insure that the ventilation system is operating at its maximum.
Potassium chloride or ammonium chloride (4-6Lbs/ton of feed) has been beneficial in reducing the mortality in acutely heat stressed flocks. These compounds replace electrolytes, which can correct the acid/base imbalances occurring during heat stress, and encourage consumption of water.

The fans and intake louvers should be cleaned. The fan belts should be tightened or changed to avoid slipping or breaking during the periods of high temperature. The inlets must be adequate to supply the airflow needed to ventilate the house during warm weather. Inadequate inlet space will throttle down the fans and decrease airflow. The inlets should be kept clean and free of anything that might restrict the flow of incoming air. Use baffle boards to direct the incoming air onto the birds.
The thermostats should be checked for accuracy. An auxiliary power system must be in place in the case of a power outage during hot weather.
In houses equipped with evaporative cooling systems, the pads should be cleaned or replaced when they become clogged. Water flow over the pads should be checked to see that it is evenly distributed across the pads. Air will flow preferentially through dry areas since there is less resistance in these areas.
Check the water filters and change if necessary. Clogged water filters can restrict the flow of fresh drinking water into the house.
Remove manure from the house often during the summer. The heat produced as manure decomposes adds to the heat load of the house. The presence of large amounts of manure can restrict the movement of air beneath slats and cages.
Do not overcrowd houses during the warm weather months.

Trace Minerals	Oxidation and Antioxidation	Immunology	Probiotics	Wingrot	Aflatoxin	Avian Gout	Quality Control in Feed Manufacturing
Ascites	Lean Tissue Deposition	Litter Management	Immunosuppression	Early Chick Mortality	Cannibalism & its management	Biosecurity	Water