ZnCP treatments had positive effect on average daily gain (ADG) (linear, P=0.005; quadratic, P = .093) of broilere during 1-21 days. The population of Escherichia coli in cecal content decreased linearly (P=0.048) and quadratically (P=0.0045) on day 21 and day 42 (linear. P=0.032; quadratic, P=0.081) with increasing ZnCP levels.