When birds get dehydrated, they have an increased risk of dying and poor start.

It is often assumed that dehydration is the result of a low relative humidity in combination with long transporting times. However, this is not the main reason for dehydration.

When birds digest feed or yolk, the metabolic water that is produced by that digestion supplies them with enough water to survive if the conditions are optimal. Additional water supply will help the birds, but additional feed has a similar effect, as the digestion will provide water as well.

When the body temperature of day old chicks gets above 40oC, they have to increase their heat loss to keep the body temperature on the desired level of 40oC. The first mechanism that they use is panting. They increase their respiration (beak open) to evaporate more water and therefore cool themselves.

Under optimal circumstances, day-old chicks will lose approximately 1 to 2 gram of body weight per 24 hours, due to moisture loss by normal breathing. Too high temperatures and with panting, will result in a significant weight loss and a significant dehydration. Under extreme situations, day-old chicks can lose 5 to 10 grams of body weight (water) in 24 hours.

When we increase relative humidity, we make it more difficult for the birds to evaporate water, and in that way we prevent weight loss. However, we also make more difficult for them to lose their body heat. And at high temperatures, that will result in an increase in mortality.

Dehydration must be prevented by controlling temperature, to keep the body temperature at the desired 40oC level, without forcing the birds to control it by panting.