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This experiment was conducted on 60 Hanwoo calves comprising five feed additive groups, with 12 calves in each group, to determine the effects of additives at pre-and post-weaning on growth performance and blood profile. The groups were control, antibiotic (Neomycin 110 ppm), illite (2%), fermented green tea probiotics (FGTP, 0.5%), and mixed additives (FGTP 0.25%, illite 1% and licorice 0.1%). The calves were offered experimental pellet feeds ad libitum and after one month were supplied with imported timothy hay. They moved freely within the group and suckled their mother's milk during the pre-weaning stage (birth to 3 months) and were separated from their dam during the post-weaning stage (4-5 months). During the pre-weaning stage, the highest average daily gain (ADG) was recorded in the antibiotic-and mixed additive-fed groups followed by FGTP, control and illite groups. In the post-weaning stage, significantly higher total weight gain and ADG were recorded in both the FGTP and mixed additive groups compared to the other groups (p<0.05). Feed efficiency of mixed additive-and illite-fed calves were almost similar with antibiotic-fed calves compared to the other two groups, but the ADG was lowest in illite-fed calves during the pre-weaning stage. In contrast, post-weaning calves fed FGTP and mixed additives showed better feed efficiency. The values of hematological indices, differential leukocyte count, blood proteins and immunoglobulin among the additive-fed calves were not significantly different (p>0.05), although hemoglobin and hematocrit values were lower in FGTP compared to control, but similar in mixed additive and antibiotic groups. These results indicate no detrimental effects of feed additives on the blood profile of calves at both pre-and post-weaning age. Serum albumin in post-weaning calves of all feed additive groups were similar but significantly lower (p<0.05) than in the control group. Post-weaning, IgM was significantly lower (p<0.05) in illite-fed calves compared to other treatment groups, but there was no difference at pre-weaning. Considering all factors, the mixed feed additives and FGTP can be the replacement feed formula for antibiotic for Hanwoo beef calf production, especially when used post-weaning.

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