During transportation, flexible behavioral responses are impossible and exposure to certain weather conditions may result in birds suffering or dying from heat or cold stress. Panting adversely alters the microclimate in the crate, making it increasingly difficult for adjacent birds to lose heat. It is therefore essential that adequate air flow is maintained to replenish the air around all birds with cooler, drier air. The rate of heat loss by convection and radiation depends on cooler and drier air. A model of such a transporter was developed at the Roslin Institute in the U.K and it seems to fit the requirements.
Heat loss is performed by blood convection to the comb, wattles and feet.
Since broilers are slaughtered when at very young age, blood cooling of the comb and wattles does not give a satisfactory solution since they are not developed enough anatomically. During cold stress, which is not very common, hypothermia is likely to occur during cold ambient temperatures when wind speeds are high. The insulating properties of feathers are significantly diminished when wet. Moreover birds may also lose more heat by convection because increased relative humidity increases the conductive properties of air. The use of tarpaulin sheeting on cold days may worsen the problem in some cases, since the material may cause a pressure drop and pull water onto the sides of the lorry, soaking the outermost birds.