Effect of different levels of monensin in diet containing extruded whole soybeans on milk production, composition and fatty acids profile of lactating dairy cows

This study was conducted to evaluate the effects of monensin supplementation in the diets of lactating dairy cows containing extruded whole soybeans seed, as the main source of protein on feed intake, milk production and composition and milk fatty acids profile. Three multiparous Holstein lactating dairy cows (third parity; 627±31 kg of weight; 81±20 days in milk; were assigned to a balanced 3×3 Latin square design. Each experimental period was 21 days with 14 days for adaptation and 7 days of data collection. The control diet was a total mixed ration (TMR) consisting of 50% forage and 50% concentrate mixture on dry matter (DM) basis. Cows were randomly assigned to one of the three dietary treatments as their main source of fatty acids (FA) with or without monensin. The first treatment was the control diet (1) of extruded whole soybeans seed without monensin. Second was control diet supplemented with 24 mg of monensin/kg of DM (2) and the third was control diet supplemented with 30 mg of monensin/kg of DM (3). Dietary supplementation with extruded whole soybeans seed with monensin had no effect on milk DMI, FCM and protein. Milk production were affected by the dietary treatments (P0.05). Although inclusion of 24 mg/Kg DM monensin in diet with extruded whole soybeans seed in the diet elevated the milk fat concentration of c9,t11- CLA but this effect was not significant (P>0.05).