Abstract
The dietary supplementation of trace minerals and probiotics has long been practiced to reduce the harmful effects of high environmental temperature in poultry. The study aimed to assess the effect of single or combined supplementation of ZnSO4 center dot H2O and probiotic (Protexin (R)) on the growth performance, gut biometry and immune organs histomorphology in broilers reared under cyclic heat stress. For this purpose, 280 day-old broiler chicks were randomly divided into seven groups designated as control (basal diet), HS (heat stress + basal diet), HS-Zn30 (HS + 30 mg ZnSO4 center dot H2O/kg feed), HS-Zn60 (HS + 60 mg ZnSO4 center dot H2O/kg feed), HS-Pro (HS + 0.1 g Protexin (R)/kg feed), HS-Zn30-Pro (HS + 30 mg ZnSO4 center dot H2O/kg feed + 0.1 g Protexin (R)/kg feed), and HS-Zn60-Pro (HS + 60 mg ZnSO4 center dot H2O/kg feed + 0.1 g Protexin (R)/kg feed). Each group consisted of five replicates (8 birds per replicate). The birds were fed on starter (0 - 21days) and grower (22 - 42 days) diets. From day 22 onwards, the birds were exposed to cyclic heat stress (temperature and relative humidity at 35 +/- 1 degrees C and 75 +/- 5% respectively) for 8 hours. The results revealed that birds exposed to heat stress showed significant decrease in body weight (BW) and increase in feed conversion ratio (FCR) compared to the control group. The dietary supplementation of ZnSO4 center dot H2O and probiotic either singly or in combination improved BW and FCR throughout the experimental period in heat-stressed broilers. Area of lymphatic nodule and lymphoid follicle in caecal tonsils and bursa of Fabricius increased in HS-Pro, HS-Zn30-Pro and HS-Zn60-Pro groups compared to HS group. In conclusion, zinc and probiotics combination partially improved performance and immune organs histomorphology in heat-stressed broilers.