| Summary: | The present study was to evaluate thyme and ajwain as antibiotic growth promoter substitutions on growth performance, carcass characteristics and serum biochemistry in Japanese quails (Coturnix japonica). A feeding trial was conducted over 28 d with 4 groups of Japanese quails fed experimental diets formulated to provide no supplementation (control), or control + 55 mg zinc bacitracin/kg, 2 g thyme/kg, and 2 g ajwain/kg. At 35 d of age, 2 quails from each replicate were sacrificed and eviscerated. Liver, empty small intestine and heart were weighed and calculated as a percentage of live body weight. The carcasses were weighed and the cuts were performed to evaluate the yield of legs and breast. At 35 d of age, 2 quails per replicate were chosen and approximately 1-mL blood samples were collected through brachial vein, and concentrations of albumin, total protein, triglyceride, total cholesterol, and high density lipoprotein (HDL) -cholesterol were determined. Final body weight were not affected by the dietary treatment whereas, it tended to increase in quails supplemented with antibiotic. Overall feed conversation ratio values were similar though it tended to improve in quails supplemented with thyme compared with other groups. Daily feed intake, internal organ weights and carcass traits were not influenced by the dietary treatments. Serum total cholesterol contents were lower (P < 0.05) in quails supplemented with ajwain compared with control and quails supplemented with antibiotic and thyme. The highest serum HDL-cholesterol was seen in the group supplemented with thyme compared with other groups. It was concluded that the addition of 2 g/kg thyme can improve serum biochemistry in quails, although its effects on performance criteria was negligible. Keywords: Quail, Thyme, Ajwain, Performance, Carcass characteristics, Serum biochemistry
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