In this study, the effects of peanut shell (PS), sodium bicarbonate (NaHCO₃) and magnesium oxide (MgO) additives to the total mixed ration (TMR) used in dairy cow feeding on rumen fluid parameters were investigated. In the study, 0.2% peanut shell (R2), sodium bicarbonate (R3) and magnesium oxide (R4) were added to the control group (R1). In addition, 0.4% magnesium oxide (R5) was added to the control group and the effect of dose interaction via MgO was examined. In order to examine the effects of the addition of PS, NaHCO3 and MgO to the ration, two different solutions with standard (S) and low (L) pH values were prepared and mixed with rumen fluid at a ratio of 2/1. The pH values in the rumen fluid mixture were determined as 7.45 in S group and 6.95 in L group. , In the study, pH value, protozoa number and viscosity values were measured at the end of 1, 2 and 4 hours of incubation. It was determined that buffering capacity of PS additive was high at low pH conditions. It was determined that low pH level had a negative effect on protozoa. The viscosity value of rumen fluid increased as the incubation period passed. While adding MgO to the ration, it was determined that 0.4% dose addition instead of 0.2% had more positive effect on rumen microorganisms. As a result, it was determined that the use of waste peanut shell in the rations of ruminant animals will provide both economic and ecological benefits.