Behavioural responses to humans and the productivity of commercial broiler chickens

Abstract

The effects of differing degrees of previous exposure to humans on the subsequent behavioural and adrenocortical responses of broiler chickens to approach and restraint by an experimenter were measured in Experiment 1. A higher proportion of birds that had received minimal human contact withdrew as an experimenter approached in a standard test than birds that had received regular human contact (0.77 vs. 0.46, P<0.05). Furthermore, these birds that had received minimal human contact had higher plasma corticosterone concentrations after 12 min of handling than birds in the latter treatment (12.61 vs. 5.40 nmol l −1, P<0.05). The usefulness of behavioural measures as indicators of the bird's fear of humans is demonstrated by these results in which handling treatments, designed to affect differentially fear of humans, caused divergence in the behavioural and adrenocortical responses of birds to humans. The major objective of the present study was addressed in Experiment 2, in which the between-farm relationships between the behavioural responses to humans and the productivity of broiler chickens were examined at 22 commercial farms. Some of the behavioural variables were significantly correlated with feed conversion (feed to gain ratio). For example, the average number of birds that approached or remained within 750 mm of an experimenter in a standard test (variable BIRDS s) and the number of birds that remained forward and oriented forward or to the side when an experimenter closely approached in another standard test (REMAIN FS) were significantly ( P<0.01 and P<0.05, respectively) and negatively correlated with feed to gain ratio (FC) at the farm. The direction of these significant correlations indicate that feed conversion was poor at farms in which birds avoided the experimenter in the two standard tests. The variable BIRDS s was found to predict FC significantly ( P<0.02), and this variable accounted for 28% of the variance in feed conversion at the farms. These significant relationships between the behavioural responses of birds to an experimenter and feed conversion suggest that fear of humans may be an important factor limiting the productivity of commercial broiler chickens. The precise mechanism(s) responsible for this inverse fear-productivity relationship in broiler chickens is unclear. However, attention is drawn to the potential for improving the productivity and welfare of commercial broiler chickens by identifying and manipulating those human factors which are influential in commercial units.