Abstract
A total of 636 1-day-old male Cobb chicks were randomly assigned to seven treatments. The chicks were offered feed and
water ad libitum throughout the experimental period. The first three groups included different stocking densities of broiler
birds (low stocking density, LSD: 23 kg/m2; medium stocking density, MSD: 34 kg birds/m2; and high stocking density
HSD: 39 kg birds/m2). The LSD group was considered a control group. The other four groups included MSD or HSD broiler
birds supplemented with either Vit E (100 mg/kg DM diet; MSDVE and HSDVE) or Zn (100 mg/kg DM diet; MSDZn
and HSDZn) in their basal diet. The main findings indicated that HSD and MSD negatively affected (p < 0.05) all variables
under investigation compared with LSD. Compared with LSD, broiler birds in the MSD and HSD groups had lower body
weights and higher feed conversion ratios, higher concentrations of blood plasma hormones (triiodothyronine thyroxine and
corticosterone), and downregulated expression levels of hepatic growth hormone and insulin-like growth factor-l. In addition,
broiler birds stocked at medium or high densities resulted in less economic return and profit. Vit E or Zn supplementation to
broiler birds stocked at medium or high densities significantly reversed all adverse effects of HSD (> 23 kg/m2) on growth
performance, hormones, and gene expression. It could be recommended that adding Zn at a level of 100 mg/kg per DM diet
allows increasing the stocking density of broiler birds from 23 kg/m2 to 34 birds/m2 while maintaining the birds, welfare