High ambient temperatures, especially above 30°C, leads to physiological and behavioural changes that negatively affect productivity. Heat stress reduces feed intake and therefore causes lower egg production as a result.

Eggshell quality is also affected because as birds pant to lose heat, there is excessive loss of CO2 in blood, which in turn causes blood pH to rise (alkalosis) and it reduces the activity of the enzyme carbonic anhydrase, resulting in lower calcium and carbonate ions transferred from blood to the oviduct, leading to fragile eggshells.

Several management practices can reduce the effects of heat stress in laying hens. Providing adequate ventilation to keep the shed under 26 oC, protecting the header tanks and water pipes from direct sunlight, flushing the drinking lines to keep the water cool, and feeding the flock during the cooler parts of the day is essential to help the flock during hot weather conditions.

Nutritional adjustments, such as the addition of potassium chloride or ammonium chloride can reduce the blood alkalosis, and the addition of sodium bicarbonate increases the availability of bicarbonate ion in blood for the deposition of calcium carbonate in the oviduct. The digestion of protein increases the heat production during digestion. Reducing the percentage of crude protein using sources of protein containing highly available amino acids and increasing the proportion of energy from highly digestible lipids, rather than starch or proteins, will reduce the heat production during digestion.

Supplements through the drinking water containing electrolytes, vitamins, chelated zinc and copper contribute to ameliorate the effects of the heat stress on the hens. Zinc also improves the activity of the enzyme carbonic anhydrase.