In this period a chicken cannot regulate its own body temperature. If environmental variables, such as air temperature and air velocity, are not optimum, it will have a direct affect on the chicken's body temperature. If this body temperature is too high or too low, a chicken will not start eating and drinking and/or will suffer from stress. The first days of a chicken's life are decisive for the technical results subsequent to the growing period. The chicken strongly depends on the ambient conditions provided by its carers (poultry farmers).