Alleviation of thermal and overcrowding stress in finishing broilers by dietary propolis supplementation

The current study investigated the efficacy of propolis supplementation (bee glue; BG) on ameliorating overcrowding and heat stress-induced impairment of growth performance, immunity, some stress indicators, and jejunum morphology in broilers. Three hundred eighty 21-d-old Ross 308 male broilers were randomly divided into 6 treatments. From d 22, the birds were either kept at thermoneutral zone (22 degrees C) or subjected to cyclic heat stress by exposing them daily to 32 degrees C for 10h (from 0800 to 1800) and 22 degrees C from 1800 to 0800. The 2 levels of stocking density include the experimental groups with low stocking density (LSD; 10 chickens/m(2)) and those with a HSD (18 chickens/m(2)). A basal diet supplemented with BG (4g/kg of diet) was fed to 2 groups, one with HSD and the other with LSD. The heat stress resulted in a significant decrease in broiler performance, coefficient of ileal digestibility (CIAD) of nitrogen (N), apparent metabolisable energy (AME), relative weight of lymphoid organs, morphometric indices, and increased mRNA levels of heat shock protein 70 (HSP70) in breast muscle. Overcrowding stress reduced performance parameters, heterophil:lymphocyte (H:L) ratio but increased levels of IgA, IgM, nitric oxide (NO), corticosterone (CS), and HSP70. Growth performance, CIAD of N, AME, relative lymphoid organs weight, and jejunum villus height were increased by BG supplementation in the chickens stocked at HSD than those housed at LSD. In addition, BG supplementation reduced blood NO and CS concentrations, and mRNA levels of HSP70 but elevated H:L ratio in heat-stressed broiler compared those reared under thermoneutral zone. It was concluded that dietary use of BG as a feed supplement can reduce some of the detrimental effects of heat stress and HSD in broilers.