singh, nitinFactors affecting pH and the mechanism of rumen pH control are poorly understood. Meta-analysis was conducted to estimate the effect of sodium bicarbonate (NaHCO3) on rumen pH. Addition of NaHCO3 increased strong ion difference (SID) and rumen pH while, volatile fatty acid concentration remained unaffected. Single-compartment model is proposed to predict the changes in rumen pH when NaHCO3 is added to diet. Prediction of model was acceptable and there were no significant mean or linear biases. An in-vitro study was conducted to determine uptake of macro-minerals by rumen microbes and the changes in SID. Differences were found in microbial mineral composition due to different pellet (liquid and solid-associated bacteria), buffer strength, pH, feed (alfalfa hay, corn grain) and length of incubation (4, 14, or 24 h). On average microbes took up more cations than anions. The values obtained from these experiments can be used to predict changes in rumen SID.en-USThesisAgriculture, Animal Culture and Nutrition