An experiment was conducted to investigate the effects of thyme (Thymus vulgaris) and satureja (Satureja khuzestanica) ethanolic extracts on the performance, blood metabolites and immune response of broiler chickens. 300 day-old Ross chicks were assigned to six dietary treatments in a randomized 2 × 3 factorial block design. Each treatment was given to five replicates of ten birds. Variables were T. vulgaris extract (0% or 1%) and S. khuzestanica extract (0%, 1% or 2%) in drinking water. Body weight (BW), feed intake (FI) and feed conversion ratio (FCR) was recorded at the end of the experiment. Serum glucose, total pro-tein (TP), triglycerides (TG), low-density lipoprotein cholesterol (LDL-ch) and high-density lipoprotein cholesterol (HDL-ch) were measured after blood sampling at 42 days of age. Specific IgG and IgM against sheep red blood cells (SRBC) were quantified six days after the injection of SRBC into breast muscle on day 23 and day 30. The plant extracts did not affect BW, FI or FCR, or the relative weights of the cloacal bursa, spleen or thymus gland (P>0.05). S. khuzestanica extract increased TG, total cholesterol and HDL-ch (P<0.05). The plant extracts did not affect the humoral immune response against SRBC (P>0.05). However, 2% S. khuzestanica extract alone, or 1% T. vulgaris extract alone or in combination with 1% S. khuzestanica extract increased the heterophil percentage (H) and heterophil:lymphocyte ratio (H/L) (P>0.05), while it diminished the lymphocyte percentage (L) (P>0.05). Breast meat pH, redness (a*), yellowness (b*) and lightness (L*) were not affected by dietary treatments. However 2% and 1% S. khuzestanica extract respectively decreased thigh meat’s pH 24 h postmortem and its a* and b* values (P<0.05). 1% T. vulgaris extract, and 1% and 2% S. khuzestanica extract, increased pH in breast meat (P<0.05). It was concluded that under these research conditions, low levels of these extracts decreased H and H/L and may be beneficial to broiler chickens’ immunity.

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