Stocking density affects the growth performance of broilers in a sex-dependent fashion.

The effects of stocking density, sex, and dietary ME concentration on live performance, footpad burns, and leg weakness of broilers were investigated. A total of 876 male and 1,020 female 1-d-old chicks were placed in 24 pens to simulate final stocking density treatments of 26 kg (LSD; 10 males or 12 females/m(2)) and 42 kg (HSD; 16 males or 18 females/m(2)) of BW/m(2) floor space. Two series of experimental diets with a 150 kcal/kg difference in ME concentration (2,800, 2,900, and 3,000 or 2,950, 3,050, and 3,150 kcal of ME/kg) were compared in a 3-phase feeding program. The HSD treatment significantly decreased BW gain and feed conversion ratio (FCR). The HSD chickens consumed less feed by 35 d of age; thereafter, the reverse was true. Male chickens had significantly higher feed intake (FI), BW gain, and FCR compared with females. A significant interaction was found of stocking density and age for FI, BW gain, and FCR. Compared with LSD treatment, HSD broilers had a higher FI and a lower FCR from 36 to 42 d of age. Stocking density, sex, and age had a significant interaction for BW gain and FCR. Female broilers had worse BW gain and FCR when stocked at high density from 36 to 42 d of age. Stocking density had no significant influence on breast, thigh, or abdominal fat yield. Female broilers had significantly higher breast yield and abdominal fat. Male broilers and HSD treatment had high footpad burn and gait scores. A low ME diet increased footpad burn score but had no effect on gait score. The result indicated that stocking density had a more severe effect on the growth of male broilers before 35 d of age. Female broilers need more space than males at similar BW per square meter near marketing age. The incidence and severity of leg weakness are associated with sex, diet, and stocking density. This result suggests that the deteriorated effect of high stocking density is sex and age dependent.