Relationship between physical activity and leg health in the broiler chicken

Why it matters

According to the researchers, there may be many causes of lameness in a broiler chicken, with the aetiology generally classified as developmental, degenerative or infectious. Poor leg health may affect the bird in several ways, with particular concern given to the possibility of pain. The differences in behaviour exhibited between sound and lame birds may indicate poor welfare caused in ways other than pain. Changes in husbandry such as stocking density or feeding regime can alleviate some causes of poor leg health. Another method found to be effective in encouraging activity in broiler chickens is providing step changes in light intensity. The authors aimed to investigate the relationship between physical activity and leg health of broiler chickens on a semi-commercial scale, exploring also the effect of step changes in light intensity on individual activity within a large flock.

Reference

The article appears in the February 2010 issue of the British Poultry Science journal (volume 51, issue 1, pages 22-30). Authors: L. Sherlock; T. G. M. Demmers; A. E. Goodship; I. D. Mccarthy & C. M. Wathes.

Abstract

The relationship between the physical activity and leg health of broiler chickens was assessed on a semi-commercial scale. Three batches of birds (2128 per batch) were raised under two lighting regimes during the photoperiod; either a step-wise change of light intensity alternating between an illuminance of 200 and 10 lx or a constant illuminance of 10 lx. The activity of focal individuals (24 per batch) was observed at 2, 4 and 6 weeks of age, and leg health assessed weekly, based on gait score, the prevalence of burns on the hock and foot pad, and angulation and rotation of the leg at the intertarsal joint. Cortical bone density and thickness and area moments of inertia of the mid-physis tibiotarsus were measured post mortem at 6 weeks of age. The step-wise change in light intensity did not affect overall performance, activity or leg health. An individual bird's activity did not affect its gait score, the prevalence of hock burn or foot pad burn, cortical density or thickness or shape of the tibiotarsus. Sex of the bird was the only factor to affect significantly the area moment of inertia in the horizontal and vertical planes of the tibiotarsus, with females showing a lower moment of inertia for both. No variable had a significant effect on cortical density or thickness. Mean cortical density was low across all birds and may indicate that, when allowed to move freely as much or as little as they choose, broiler chickens do not exercise enough or do not perform the higher impact activities required to affect bone quality. These findings imply that the activity of broiler chickens raised on a semi-commercial scale is unaffected by step-wise changes in light intensity and that other husbandry measures are needed to raise activity and hence improve leg health.