The effects of garlic (Allium sativum) and thyme (Thymus vulgaris) extracts and a probiotic on growth performance, intestinal tissue morphology, and microbial flora in broilers were investigated. A total of 240 Ross 308 male broilers were divided into 4 treatments, with 4 replicates of 15 birds. Treatments were 2 plant extracts (1,000 ppm) and the probiotic (1,000 ppm from 0 to 7 d, 500 ppm from 8 to 21 d, and 250 ppm from 22 to 42 d) added to drinking water, and a control group with no additives. Birds in different treatments received the same diets during the experimental period. Feed intake, BW gain, and FCR were not influenced by the treatments. The weight of the ileum in birds receiving garlic was significantly lower than that in birds receiving thyme. The villus width in the duodenum of birds receiving garlic was lower than that of birds in control group (P < 0.05). A smaller villus width in the ileum was seen in birds fed garlic and the probiotic compared with birds fed the control diet. However, villus height and crypt depth were not affected by the treatments. At 20 d, birds fed garlic had significantly higher lactobacillus and lower coliform counts compared with birds fed the probiotic. Chickens that received thyme had lower total aerobic bacterial counts in the ileum than did birds in the control group. At 40 d, birds receiving the probiotic had higher total aerobic bacteria and lactobacillus counts in the crop than did birds receiving the control diet. It was concluded that these plant extracts and the probiotic can be used as natural growth promoters for broilers. The beneficial effects of plant extracts and the probiotic should be further studied on commercial farms.

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