Effects of stocking density on growth performance, growth regulatory factors, and endocrine hormones in broilers under appropriate environments.

Stocking density is an important environment factor that affects the development of poultry farming, which has caused widespread concern. This study was carried out to determine the effects of stocking density on growth performance, growth regulatory factors, and endocrine hormones in broilers under appropriate environments. A total of 144 Arbor Acres male broilers (BW 1000 ± 70 g) were randomly divided into low stocking density (LSD; 6.25 birds/m2), medium stocking density (MSD; 12.50 birds/m2), and high stocking density (HSD; 18.75 birds/m2) groups, with 6 replicates in each group, and raised in 3 environmental chambers (same size) from 29-day-old to 42-day-old, respectively. The trial period lasted for 14 D with 21 ± 1°C and 60 ± 7% relative humidity, wind speed < 0.5 m/s, ammonia level<5 ppm. The results indicated that average daily food intake and average daily gain in HSD group showed significantly lower than other 2 groups (P < 0.05). Besides, the HSD group significantly reduced breast muscle yield, tibial length, tibial width, and tibial weight of broilers (P < 0.05). The HSD group increased the mRNA expression level of myostatin, and reduced the mRNA expression levels of insulin-like growth factor 1 (IGF-1) and myogenic determination factor 1 (P < 0.05). The HSD group significantly reduced the expression of parathyroid hormone-related protein in tibial growth plate (P < 0.05). The HSD group increased the serum corticosterone levels of broilers (P < 0.05), and decreased the serum IGF-1 and thyroxine (T4) levels of broiler chickens (P < 0.05) than other stocking density groups. Moreover, the serum alkaline phosphatase levels were decreased (P < 0.05) with increasing stocking density, whereas there were no significant effects on the serum 3,5,3'-triiodothyronine (T3) concentrations in 3 groups (P > 0.05). In conclusion, under appropriate environments HSD reduced the growth performance of broilers and this negative effect was likely associated with decreased growth of muscle and bone.