This study investigated the responses of low-weight day-old chicks to
zinc bacitracin and Bacillus mixture on growth performance,
hematology, intestinal selected microbiota populations, and carcass
characteristics. A total of 192 unsexed Lohman MB-202 day-old broiler
chicks were randomly allotted to four dietary treatment groups of 48
chicks each (6 replicates of 8 chicks) and fed for 35 days. The four
treatments were CONT (basal diet without supplementation), AGP
(basal diet with 0.04% zinc bacitracin), PROB (basal diet supplemented
with 0.5% Bacillus mixture), and PROB+AGP (basal diet supplemented
with 0.5% Bacillus mixture and 0.04% zinc bacitracin). There were no
significant differences in final body weight, feed intake, and feed
conversion ratio of broilers. The relative weight of thymus was higher
(P= 0.01) in AGP than that in PROB and PROB+AGP birds. Birds in
PROB+AGP had lower (P= 0.04) values of alanine aminotransferase
(ALT) enzyme compared to those in CONT and AGP groups, but the
difference was not significant when compared with birds in PROB
group. Serum creatinine was lower (P < 0.01) in PROB+AGP than in
CONT and AGP birds. Birds in AGP group tended (P = 0.09) to have
higher globulin concentration in the serum compared to other birds.
There was also a tendency (P = 0.07) for PROB+AGP birds to have
higher albumin to globulin ratio compared with other birds. There was
more lactic acid bacteria in ileal digesta (P = 0.05) in PROB+AGP than
in AGP birds, but the difference was not significant when compared to
CONT and PROB birds. Birds in AGP group had higher (P = 0.05)
relative breast weight compared to other birds. In conclusion, Bacillus
mixture did not affect performance and hematological parameters, but
increased the intestinal population of lactic acid bacteria in broiler
chicks