Effects of age and stocking density on leg weakness in broiler chickens.

The effects of stocking density (STD) on leg weakness in broiler chickens was assessed in two trials. The interaction between age and STD on leg weakness was further evaluated in one trial. In Trial 1, walking ability was assessed at 28, 42, and 49 d of age. Birds were stocked at 833, 625, or 435 cm2 per bird. In Trial 2, birds were stocked at 625 or 455 cm2 per bird and assessed for tibial dyschondroplasia (TD) by radiographic examination at 28 d and walking ability at 35 d. Foot pad burn, hock burn, and angulation of the hock joint were also assessed at slaughter on Day 42. Body weight was measured during both trials. At 4 wk of age, leg weakness was a relatively minor problem; few severely lame birds had a gait score (GS) of 4 or 5 at any density. However, 2 wk later, the birds had substantially poorer walking ability. Further deterioration had occurred by 7 wk of age. At all ages, males exhibited greater leg weakness than did females, and the proportion of severely lame birds increased with age of assessment. The effect of STD was consistent across both trials; higher STD were associated with poorer walking ability and reduced live weights. In Trial 2, higher STD resulted in more foot and hock burns. Females were more sensitive to STD than were males However, there was no effect of STD on the prevalence of TD or angulation of the hock joint. The effect of high STD on walking ability was apparent even at 4 wk of age. Adjusting the observations for differences in BW did not alter the findings. It was concluded that the lower STD substantially reduced the prevalence of leg weakness.