Effects of using an oregano aqueous extract on performance, gut microbiota and immune function in broiler chickens.

A total of 150, 1-day-old female broilers (Ross 308) were divided into 2 groups of 75 birds each and fed a starter diet from 1 to 21 days and a grower-finisher diet from 22 to 56 days. The two experimental diets were based on a standard commercial feed used as control (C group) which was supplemented with 2 g/kg oregano aqueous extract (OAE) (O group). Individual body weight (BW) and feed conversion efficiency (FCE) were measured. Blood samples from 5 chickens/group were collected for IgG titration at 22 (T1) and 57 days (T2). At the same time intervals, 8 samples were collected for intestinal microflora examination. Physico-chemical parameters were determined on 10 breast meat samples of both groups. The OAE supplementation affected the BW of birds (P<0.01) up to 22 d of age, while no effects were observed at 36 d and at the end of the experiment. A numerically lower FCE was observed at 36 and 57 d in birds fed the OAE diet. Although the dietary treatment did not appear to affect mean serum IgG values in terms of absolute numbers, their increases (expressed in percentages) from T1 to T2 revealed a significant (P<0.05) dietary effect with the highest value in the O group. Regarding gut microbiota data, coliforms were lower (P<0.001) in the cecum of the O group. The Enterococcus spp. resulted higher in the OAE group (P<0.001), particularly in the caecum tract, and its value increased at T2, supporting the hypothesis of a time-dependent effect. Birds in the C group showed the highest values for Lactobacilli in the ileum and cecum tracts at T1. Values increased (P