This experiment was conducted on 40 newborn Holstein female calves comprising two experimental groups, with 20 calves in each group to investigate the effects of Macleaya cordata extract (MCE), on calf body weight and health which added to milk replacer. In both group calves fed on the same terms. Differently, 10 g /head/ day dosages MCE added to the milk replacer of the trial group from day 3 to day 25. Afterward, calves continued to feed until 3 months old and weighed on the birth, 15th,

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... 60th and 90th days. At the end of the experiment, there was no significant difference at the weights on the birth and 15th days. However, on the 40th, 60th and 90th days weighing in favor of the control group, a significant difference was found (P<0.05). At the end of the experiment in favor of the trial group, there was a significant difference with clinical pneumonia and aspiration pneumonia (P<0.05). The results obtained in the research; MCE which added the milk replacer as a feed additive indicated no positive effect on calf body weight. From a health point of view, MCE has reduced the incidence of respiratory diseases in particular.