Concentration of blood urea nitrogen (BUN) of calves at age of10 wk in group 10 wk had no significant difference with the control group but greater than that in the group 4 wk, 6 wk, and 8 wk. Concentration of BUN of calves at age of13 wk and 22 wk in group 4 wk, group 6 wk, group 8 wk and group 10 wk were less than that in the control group (p<0.05).
In our study, calves weaned at 8 wk and 10 wk had no significant difference of feed efficiency with those weaned after 22 wk, but calves weaned at 4 wk and 6 wk had significant higher feed efficiency than calves in group 8 wk and 10 wk in 11 to 13 wk, and calves weaned off at 4 wk and 6 wk had significant higher feed efficiency with those in group 10 wk in 14 to 22 wk, but no significant difference with calves in group 8 wk. Collectively, weaning calves as early as 4 or 6 weeks age increased their feed efficiency.
However, the WBC concentration of birds in the COS0.4 and ANTCOS group were higher (p<0.05) than that of birds in other groups at the end of the 6th wk.
In addition, the difference in WBC counts between the beginning and end of the experiment in COS0.4 and ANTCOS groups were significantly higher (p<0.05) than that of CON and ANT groups.