Abstract
Broiler chickens are increasingly at the forefront of global meat production but the consequences of fast growth and selection for an increase in body mass on bird health are an ongoing concern for industry and consumers. To better understand the implications of selection we evaluated energetics and behaviour over the 6-week hatch-to-slaughter developmental period in a commercial broiler. The effect of posture on resting metabolic rate becomes increasingly significant as broilers grow, as standing became more energetically expensive than sitting. The proportion of overall metabolic rate accounted for by locomotor behaviour decreased over development, corresponding to declining activity levels, mean and peak walking speeds. These data are consistent with the inference that broilers allocate energy to activity within a constrained metabolic budget and that there is a reducing metabolic scope for exercise throughout their development. Comparison with similarly sized galliforms reveals that locomotion is relatively energetically expensive in broilers.
Highlights
Broiler chickens are increasingly at the forefront of global meat production but the consequences of fast growth and selection for an increase in body mass on bird health are an ongoing concern for industry and consumers
Changes in behaviour were correlated with increasing body mass until a breakpoint value of 0.911 ± 0.135 kg (Davies’ test P < 0.001), after which further declines in performance were negligible
Across the size range studied, broiler cost of transport (CoT) follows a negative relationship with increasing body mass (Fig. 4b, Table 2), indicating that locomotion becomes energetically cheaper on a mass-specific basis in larger birds
Summary
Broiler chickens are increasingly at the forefront of global meat production but the consequences of fast growth and selection for an increase in body mass on bird health are an ongoing concern for industry and consumers. For each bird in the chamber, the magnitude of RMRstand: RMRsit was calculated according to body mass using the relationship determined in our analysis of postural energetics.
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