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

Abstract

This experiment was conducted to investigate the effect of <em>in ovo</em> feeding (IOF) and dietary feeding of <em>Silybum marianum</em> (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 <em>in ovo</em> 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 <em>infectious bursal disease</em> (IBD) by feeding extract. White blood cell counts was significantly higher (P<0.01), and heterophile/<em>lymphocyte</em>(Het/Lym) ratio was lower in dietary-feeding SMextract 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 <em>in ovo</em> feeding of the extract had no much impact on immunity parameters.