Effects of thyme and oregano on growth performance of broilers from 4 to 42 days of age and on microbial counts in crop, small intestine and caecum of 42-day-old broilers

This study evaluated the effects of thyme (experiment 1) or oregano (experiment 2) on growth performance and gastrointestinal microflora in broilers. In each experiment a total of 120 four-day-old Ross 308 boiler chickens were assigned to the basal control diet or the basal diet supplemented with either 10, 15, 20, 25 or 30 g/kg of thyme or oregano (n = 10 per diet, each replicate consists of two birds). Overall growth performance of the broilers fed the basal diet was below standards with 42-day body weights ranging from slightly above 1500 g to about 1900 g. As all diets including the control had the same energy and nutrient concentrations, this should not compromise the comparison among the diets. Improvements for body weight gain and feed conversion ratio (P < 0.05) were observed in both experiments, however feed intake was increased (P < 0.001) only by oregano addition. Colony forming units of Lactobacillus spp. were reduced (P < 0.05) for thyme and oregano supplemented groups, whereas no changes were observed for colony forming units of total plate counts. In conclusion, thyme and oregano supplemented at 15 or 20 g/kg diet can be used as effective feed additives to improve performance of broilers.