Osmolality, pH, products of fermentation, volume and temperature of the fermentation vat are regulated.
Microorganisms living in the rumen depend for their survival on the food that the animal eats.
Population shifts may occur with some species of microorganisms increasing in numbers and other species being eliminated. The pH of the ruminoreticulum, which is usually in the range 5.8-7.0, decreases after feeding. A fall in pH is especially marked when the diet contains large amounts of fermentable carbohydrate. During fasting, the concentration of VFA decreases and the pH of the rumen liquid may rise above 7.0. The speed at which carbohydrates are fermented in the rumen varies with their accessibility.