HERTFORDSHIRE/UK, April 12th (Biermann) – Dr. L. Sherlock, from The Royal Veterinary College, Hertfordshire, and colleagues raised three batches with each 2128 broiler chickens. The birds 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 investigators observed the activity of focal individuals (24 per batch) at 2, 4 and 6 weeks of age. Leg health was assessed weekly, based on gait score, as well as the prevalence of burns on the hock and foot pad, and angulation and rotation of the leg at the intertarsal joint. Furthermore, cortical bone density and thickness and area moments of inertia of the mid-physis tibiotarsus were measured post mortem at 6 weeks of age.

Analysis showed that the step-wise change in light intensity did not affect overall performance, activity or leg health. Apart from that, the researchers found, that 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," Sherlock and colleagues report. However, they add, 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.

The authors conclude "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."

References

• British Poultry Science, Volume 51, Issue 1 February 2010 , pages 22 - 30