Introduction

This study was conducted to investigate the efficacy of monensin on milk fatty acid profile in Holstein dairy cows. For this study 12 cows with initial weight 625 ± 48 kg were allocated to control group and monensin group, with 6 replication in each group using completely randomized design (CRD). The experiment was accomplished during 21 days including pre trial period (14d) and feedlot period (7d). Diet was given twice daily to each group. The conjugated linoleic acid content of diets with monensin was higher than other and there were significant differences (P < 0.05).