Effects of zinc methionine and selenium yeast on growth performance, antioxidant capacity, immune function and intestinal morphology of broiler chickens under heat stress

1. This study evaluated the effects of zinc methionine (Zn-met) and selenium (Se) yeast on growth performance, antioxidant capacity, immune function and intestinal morphology of broiler chickens under heat stress (HS).2. A total of 54, yellow-feather male broilers (35-d old) were randomly allocated to one of three groups; a control group (CON) fed a basal diet and maintained at 26 ± 1°C, a group fed the basal diet with cyclic HS alone or + Zn-met + Se yeast group (HZS) fed a basal diet supplemented with 250 mg/kg Zn-met and 150 mg/kg Se yeast. After the 7-d prep-trial period, the birds in the HS and the HZS groups were exposed to cyclic HS treatment (30 ± 1 to 34 ± 1°C) from d 8 for 2 weeks.3. The HS treated birds had reduced body weight, daily gain, feed intake and feed conversion ratio (<i>p</i> < 0.01) and increased mortality and rectal temperature, whereas the HZS group had a lower mortality rate and rectal temperature. The HS group had higher blood triglyceride (<i>p</i> < 0.01) and lower potassium (0.05) levels than the CON group. Exposure to HS increased the lipopolysaccharide levels (<i>p</i> < 0.05) and decreased the levels of immunoglobulin (Ig) A and IgG (<i>p</i> < 0.05), which were improved in the HZS group. The HZS group reversed the increase in blood catalase activity caused by heat stress and increased glutathione peroxidase levels (<i>p</i> < 0.05). Heat stress decreased villus height in the duodenum and jejunum, increased the crypt depth and decreased the villus height to crypt depth ratio in the small intestine, which were improved in the HZS group (<i>p</i> < 0.05).4. Dietary supplementation with Zn-met and Se yeast was shown to be an effective nutritional regulation strategy for alleviating any negative effects of heat stress in broiler performance.