The trial included 32 Holstein dairy cows with an average milk yield of 10,005 litres in the previous lactation. In each group, 8 were selected for sampling rumen fluid and of which in each group 4 for monitoring the pH and temperature in rumen boluses eCOW use. The experimental period lasted 12 weeks, respectively 4 periods after three weeks. In the first period, group A received a ration (TMR) with a control (K) compound feed (KS) D01K and a group B TMR with a KS D01R containing 5% of formulation R. At the end of each period, the KS was replaced. Dairy cows, fed a ration experimental group was statistically significant (P 0.05) was the amount of milk milked. Key words: rumen; milk; feeding; pH; bolus eCOW