RESUMO
BACKGROUND: Heat stress is one of the most critical problems confronting the poultry industry. Stinging nettle (SN) is a medicinal plant with potent antioxidant properties. OBJECTIVE: The goal of this study was to evaluate the effects of dietary SN at two different levels (2 and 4%) on the serum levels of cortisol and some selected parameters of broilers exposed to chronic heat stress. METHODS: A total of 240 broiler chickens were randomly assigned to six dietary groups as follows: (1) control: fed the basal diet; (2) HS: heat-stressed broiler fed the basal diet; (3) HS-SN2: heat-stressed broiler fed 2% dietary SN; (4) HS-SN4: heat-stressed broilers fed 4% SN; (5) SN2: no heat-stressed broilers fed the basal diet supplemented with 2% SN; (6) SN4: no heat-stressed broilers fed the basal diet supplemented with 4% SN. Diet supplementation with SN was performed from days 14 to 35 and chronic heat stress was induced from days 22 to 29. The serum parameters were evaluated on days 14, 21, 29 and 35. RESULTS: HS had higher serum levels of cortisol, total cholesterol (TC), aspartate aminotransferase, alanine aminotransferase and creatine kinase (CK) compared to the other treatments. HS-SN4 had significantly lower cortisol, TC, alanine aminotransferase and CK compared to HS and HS-SN2. CONCLUSIONS: The inclusion of 4% SN powder in the broilers' diet alleviated the negative effects of heat stress by decreasing cortisol, TC and tissue damage indices. It seems that dietary SN could be used as a feed additive in the poultry diet for improving the health status and defence mechanisms of the birds under stressful conditions.
