Effects of Scrophularia striata extract, vitamin E, vitamin C, and selenium on performance, immune response, and blood parameters of broilers under heat stress conditions

To evaluate the effect of hydroalcoholic extract of Scrophularia striata (SSE), vitamin E, vitamin C, and selenium on performance, blood parameters, and immune response of broilers under heat stress conditions, an experiment was performed using 350 one-day-old male broilers (Ross 308) in a completely randomized design with seven treatments and five replicates (10 chickens per replicate). Experimental groups were a group under normal environmental conditions (negative control), a group under heat stress (positive control), and other groups under heat stress and fed with the diet supplemented with 200 ppm vitamin E, 500 ppm vitamin C, 0.3 ppm selenium, or 200 and 400 ppm SSE. From day 1 to the end of the breeding period, a temperature of 34 ± 2 °C was applied to create heat stress for 8 h (10 am to 6 pm). The results showed that all treatments improved (P<0.05) body weight gain, feed conversion ratio, performance index, heterophil to lymphocyte ratio, total and IgG titers against sheep red blood cells, and cellular immunity (toe web swelling skin in response to phytohemagglutinin injection), and the best performance was observed in the negative control, high SSE and vitamin E, respectively. All experimental treatments, except for low SSE and selenium treatments, increased blood lymphocytes and potassium compared to the positive treatment (P<0.05). In general, the inclusion of 400 ppm of SSE in the diet had a beneficial effect on growth performance, blood parameters, and immune response during heat stress.