Impacts of Heat Stress on Some Performance Parameters of Broiler Chicken Reared Under Different Stocking Densities

The current study was designed to investigate the impacts of heat stress (HS) on performance parameters of broiler chicken reared at different stocking densities, also study assessed the effects of anti-stress (vitamin) supplementation in the mitigation of different levels of stress. A total of 720 7th-day-old Cobb ® chicks were randomly distributed into 18 groups, (two replicates within each group). The experiment with a factorial arrangement of treatments (3x3x2), 3 levels of stocking densities (RSD: 10 chicks/m2, MSD: 14 chicks/m2, and HSD: 18 chicks/m2), 2 levels of vitamin supplementation (0 mg/l and combination of 250 mg/l ascorbic acid plus 0.5 ml/l Vit E + Se) and three temperatures (Thermoneutral temperature (TN), sudden chronic heat stress exposure (CHS) and gradual chronic heat stress exposure). Broilers were kept either under thermoneutral conditions (24 ± 1 ºC) during the whole life period or slowly introduced to CHS from 7th to 21st d of age and kept at high temperature thereafter and the third chamber had chicks that were exposed to CHS (32 ± 2 ºC for 8 h/day) during the period from 21st: 42nd day of age. Chicks were reared on a deep litter system and had free access to feed and water. Performance parameters (FI, BW, BWG, and FCR) were determined on the 42nd day of age. The results showed HSD had adverse effects on the growth performance of broilers reared under thermoneutral or CHS conditions where the differences between densities were significant (P<0.05) under TN and sudden CHS conditions and insignificant in case of gradual CHS exposure conditions for most of the performance parameters. Vitamins supplementation had improved growth performance (BW and FCR) of broilers kept under MSD or HSD and exposed to thermoneutral or sudden CHS conditions as compared to corresponding not supplemented birds. While it was effective in combating the adverse effects of gradual HS exposure in RSD and MSD kept broilers only. In addition, there was no significant difference between RSD not supplemented broilers and MSD-supplemented birds under TN conditions; concluding that broilers can be stocked at MSD under thermoneutral conditions if they were supplemented with vitamins.