When dairy cows feed on chewy feed, the microorganisms attach to the feed particles by forming a thick mucus like biofilm, which acts as a bridge between microorganisms and feed particles. Next, these microbes begin to multiply at the attachment site to form colonies and secrete digestive enzymes. Rumen microorganisms can cooperate with each other to complete adhesion and fermentation to fully digest the diet.
The decomposed food carbohydrates (cellulose, hemicellulose, pectin, starch, sugar) are converted into volatile fatty acids (VFA) under the action of microorganisms. They are absorbed by rumen wall and enter the liver with blood circulation. In the liver, they are converted into energy substances needed by dairy cows. Among them, acetic acid, propionic acid and butyric acid are the three main VFA. Acetic acid is mainly produced by cellulose decomposing bacteria, which is usually related to the synthesis of milk fat. Propionic acid is mainly produced by starch decomposing bacteria to decompose starch and sugar. In short, propionic acid is the main energy source (glucose) for milk production and weight gain of dairy cows.Butyric acid is produced by specific butyric acid decomposing bacteria or body fat mobilization, which can use other VFA to form butyric acid, which is also related to milk fat synthesis.