Effect of age and presence of perches during rearing on tonic immobility fear reactions of broiler breeder pullets.

Broiler breeders were housed in pens in an all-litter house with an 8-h photoperiod from hatching to 20 wk of age. They were reared either in the presence or absence of perches (7 cm per bird) and on either a 14% or a 17% CP diet. The duration of the tonic immobility (TI) fear response was measured in 15- and in 20-wk-old birds; each pullet was tested individually and once only. There was an apparent age-related increase in the duration of TI, which was attenuated by the provision of perches during rearing. The results are discussed in terms of maturational and environmental influences on the development and alleviation of fear.