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

The effects of stocking density (STD) on leg weakness in broiler chickens w as assessed in two trials. The interaction between age and STD on leg weakn ess was further evaluated in one trial. In Trial 1, walking ability was ass essed at 28, 42, and 49 d of age. Birds were stocked at 833, 625, or 435 cm (2) per bird. In Trial 2, birds were stocked at 625 or 455 cm(2) per bird a nd 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 w as measured during both trials. At 4 wk of age, leg weakness was a relative ly minor problem; few severely lame birds had a gait score (GS) of 4 or 5 a t any density. However, 2 wk later, the birds had substantially poorer walk ing 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 i n more foot and hock burns. Females were more sensitive to STD than were ma les However, there was no effect of STB on the prevalence of TD or angulati on of the hock joint. The effect of high STD on walking ability was apparen t 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.