RESUMEN
This study was conducted to evaluate the effect of a blend of essential oils (EOB) derived from thyme (Thymus vulgaris), peppermint (Mentha piperita) and eucalyptus (Eucalyptus globules) as a natural growth promoter. Five dosages (0 (CON), 50, 100, 150 and 200 ppm) of EOB were added daily to the drinking water to determine its effect on growth performance, carcass quality, blood biochemistry, immune response and ileal morphology in Ross 308 broiler chicks. A total of 500, 10-day-old male Ross 308 broilers were allocated into five treatments with four replicates each. Inclusion of EOB at 150 ppm improved (p < 0.05) body weight gain, feed conversion ratio and production index by 11.73, 10.81 and 24.13% compared to CON respectively. The inclusion of EOB at 100, 150 and 200 ppm increased (p < 0.05) carcass yield and thigh muscle compared to CON. Serum concentration of hepatic enzymes (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase) was decreased while the ileal villus height and ratio of villus height to crypt depth were improved (p < 0.05) in response to inclusion of 150 and 200 ppm of EOB compared to CON. The ileal Escherichia coli count was lower and Lactobacillus count was higher in EOB-200 and EOB-150, respectively, compared to CON at 21 and 42 days of age (p < 0.05). Antibody titre of Newcastle, bronchitis and infectious bursal disease was linearly increased (p < 0.05) by increasing supplemental level of EOB at day 4 post-inoculation. Our results suggested that supplementation of EOB at the 150 ppm into drinking water during day 11-42 could improve growth performance, humoral immunity and ileal morphology and microflora in broilers, and thus, EOB has merit to be used as an alternative to antibiotic growth promoters.
