Effect of in ovo Feeding and Dietary Feeding of Silybum marianum Extract on Performance, Immunity and Blood Cation-Anion Balance of Broiler Chickens Exposed to High Temperatures

This experiment was conducted to investigate the effect of in ovo feeding (IOF) and dietary feeding of Silybum marianum (SM) extract on the immunity of chicken under heat stress conditions. A total of 360 fertile eggs from a commercial broiler breeder (Ross-308) farm was used for in ovo feeding of 0, 100 and 200 mg/L SM water extract at day 17.5 of incubation. After hatching, 240 chicks were transferred to the experimental cages. Two types of diet were used; one of them without extract and the other one containing 100 mg/kg of SM extract. Then chicks were exposed to elevated temperatures 4 °C above optimum from 7 to 28 days of age for 4 h daily and then they were kept at the optimum temperature. The chicks were divided into six treatments with four replicates as a completely randomized design with 2 × 3 factorial arrangement. The results showed that chicks fed diet containing the extract had the highest feed intake, daily weight gain and final body weight and lowest feed conversion ratio (P 0.01). At 28 and 42 days, dietary feeding of the extract increased the relative weights of bursa (P 0.05), thymus and spleen (P 0.01) significantly. Results showed a significant increase (P 0.05) in antibody titer against infectious bursal disease (IBD) by feeding extract. White blood cell counts was significantly higher (P 0.01), and heterophile/lymphocyte (Het/Lym) ratio was lower in dietary-feeding SM extract treatments (P 0.01). The dietary feeding of extract increased blood cationic charge (Na^+ and K^+) at 28 d and led to increase cation-anion equation (P 0.01). However at 42 d, effect of dietary feeding of extract on these parameters was not significant. The ash percentage was significantly higher in chicks fed 100 mg/kg of extract at 28 d (P 0.01). It seems that dietary feeding of the extract to broiler chickens considerably increased immunity response under elevated temperatures, but in ovo feeding of the extract had no much impact on immunity parameters.