In tropical countries like Nigeria, hot weather is a common problem where temperature can rise above 30^oC. It is a well-known fact that hot weather leads to poor performance in birds. It leads to low feed consumption and high water intake. Layers under hot weather will lay fewer eggs, grow slower, easily get sick (think Newcastle disease), lay small eggs, watery eggs and eggs with thin shells. In broilers, growth rates, feed efficiency, immunity and carcass quality will be negatively affected. In breeders, egg hatchability is negatively affected.

For optimum performance, chickens require a temperature and humidity range of 18-24°C (65-80°F.) and 60-80% relative humidity. For every 1^oC lower than 20^oC, the bird will consume extra 1.5g of feed per day (5). When temperature rises above 24^oC, egg weight and shell quality tend to suffer.

Signs of Heat Stress

Signs of a heat-stressed bird are panting, holding the wings out, wings droop and are held slightly away from the body, standing or lying down, and closed eyes.

Birds can tolerate gradual increase in temperature but sudden change to very high temperature will lead to heavy mortalities.

Feeding Strategies

There are various methods of minimizing heat stress, but we’ll be focusing on the feeding aspect.

1. Increase Nutrient Density of the Feed

This applies if you formulate your own feed. When the weather is hot, the birds eat less and at the end of the day, they won’t eat enough to meet their nutrient needs. This can be solved by increasing the nutrient density of the feed.  If layers that are supposed to eat 125g/bird/day are eating 100g/bird/day, they’re loosing all the nutrients in 25g of feed. By formulating your feed base on 100g/bird/day, you can include all the nutrients they need in it.

a. Energy Content

The energy content of the feed should be increase using fat because fat metabolism produces less heat than carbohydrate metabolism. Fat also increases palatability of feeds. However, beware that fat are prone to rancidity and you should prevent this by including antioxidants and antitoxins in the feed.

b. Protein Content

Protein content should be increased from 16% to 17-18%. A better alternative is to increase and balance essential amino acids because increase in protein level can increase heat production during protein metabolism. What animals need is not protein, but the amino acids it contains. So even if a diet is low in protein but the amino acid content is balanced, performance will not be affected. If protein level must be increased, use protein from vegetable sources (soya, sesame, sunflower etc) since those from animal source will produce more heat during metabolism. Vegetable proteins are rich in arginine (an amino acid), an important protein needed during heat stress.

c. Feed a Source of Calcium Carbonate

The calcium content of the diet should be increased base on feed intake, such that each bird consumes the right amount per day. For laying hens, top dressing feed with oyster shell or large particulate limestone is beneficial and can stimulate feed consumption. Limestone and oyster chips can be given at a rate of 625 g per 100 hens.

d. Supplement Minerals and Vitamins

To avoid imbalances in acid-base balance due to heat stress, various compounds can be added in the diet or water. These include sodium bicarbonate (NaHCO3), potassium chloride (KCl), calcium chloride (CaCl2), ammonium chloride (NH4Cl) and vitamin C (ascorbic acid). Ascorbic acid and NaHCo3 seems to be the most popular in the tropics. Sodium zeolite and aspirin are also beneficial in reducing the effects of heat stress in laying hens. Commercial anti-heat stress packs are also available.

Stressors such as diseases and heat stress may increase the chickens’ need for vitamin C.  Vitamin C is needed for amino acid and mineral metabolism as well as for synthesis of hormones. It is also needed for the synthesis of sex hormones such as testosterone, which is essential to the reproductive performance of males. Adding vitamin C in drinking water at a rate of 40 milligrams per bird per day is beneficial for broilers while laying hens need 20 milligrams per liter of water. Alternatively, vit. C can be added to feed at 150-400g/ton. Vitamin E can be added at 50-100ppm in feed (i.e. 0.005-0.01g/kg feed).

Aspirin can be used for its antipyretic (cooling) effect at the rate of 0.3 grams per litre of water. Research has shown that sodium bicarbonate at high temperature stimulates water and feed consumption as well as contributing to improved weight gain. 8 grams of sodium bicarbonate in 100 litres of water can stimulate water consumption in stressed broilers (Butcher & Miles, 2003). For broiler breeders, 0.05 to 0.30% are reported to give beneficial results (Naseem et al., 2005).

In moderately hot weather, you can use the following combinations per liter of water:

62.5mg/l Ascorbic acid + 62.5mg/l Acetylsalicyclic acid (aspirin) + 75mg/l sodium bicarbonate + 125mg/l potassium chloride.

In heat stress condition, use the following:

400mg/l vitamin C + Electrolytes (as recommended by manufacturer) + Acetylsalicyclic acid (Disprin 1 tablet/5l) + 1g/l sodium bicarbonate

2. Increase Feed Consumption

Low feed consumption under high temperature is the main cause of poor performance. The strategies below can help you increase feed consumption.

1. Give feed with good physical quality as this will encourage birds to eat more.
2. If there is enough floor space, add extra feeders.
3. Don’t store feed for more than 2 months when it is hot. This reduces the possibility of mycotoxin build up.
4. Feed the birds at cooler times of the day – early morning and evening.
5. Remove feed 4 to 5 hours prior to an anticipated heat stress period. Feed intake and digestion can produce nearly 7% additional heat which is maximum 4-5 hours after feed intake. This should not coincide with the hottest part of the day (2-3pm), so feed can be withdrawn at 9am till 4pm. But note that if biosecurity is poor, feed withdrawal may lead to coccidiosis or necrotic enterisis, so keep medication at hand. Note: The anticoccidials, Nicarbazine and Monensin should not be used in hot weather. The former decreases tolerance to heat and the later depress water intake.
6. Birds should not be fed or disturbed during the hottest part of the day.
7. Midnight feeding: For laying hens, this involves turning the lights on for 1 hour in the middle of the night so that the hens can eat more and increase their production level. You can start this when 5% of the flock start laying and stop at any time or when the birds have achieved the desired bodyweight. The 1 hour of light can be added all at once. But when you want to remove it, do so gradually at the rate of 15 minutes per week.

Midnight feeding will increase feed intake by about 2-5 g/day per bird. This technique can be used any time more feed intake is desired in either growing pullets or laying flocks. For other poultry like broilers where light control is not necessary, night feeding is advisable. In that case you don’t need to pay attention to how long you leave the lights on, but you have to give them enough dark periods for rest.

3. Supply Cool Water

Cool water at 10-12^oC is helpful. Protect water tanks and pipes from sun because birds will reject warm water. Water at 5^oC during the hottest part of the day will help reduce the effect of heat stress.

Conclusion

Heat stress results in lower feed intake and higher water intake. The decline in feed intake leads to poor bird performance. There is no single solution to heat stress so using a combination of solutions listed here is recommended. Also see other methods of minimizing heat stress apart from manipulating feeding.