The Absorption of Volatile Fatty Acids from the Rumen

Abstract

1. Mixtures of acetic and propionic acids introduced into the rumen at pH 8.5 showed no significant changes in the relative proportions of the acids in a period of 6 hr. 2. Pectin was shown to remain unchanged and unabsorbed in the ‘isolated’ rumen. By using it as a marker the course taken by fatty acids introduced into the empty rumen was followed. The acids found their way from the rumen, in part by absorption through the rumen wall and in part by passing on to the abomasum. 3. Absorption of both acetic and propionic acids took place readily at acid reactions. Between 10 and 14% of the acetic acid and about 47% of the propionic acid introduced was absorbed within 6 hr. The amounts absorbed were not altered by the inclusion of inorganic phosphate in the mixture. Absorption did not occur to any significant extent from similar solutions introduced at reactions≥pH 7.5. 4. In two experiments acetic acid was not absorbed from an ‘isolated’ rumen when introduced as a slightly alkaline (about pH 7.5) solution of sodium acetate. Recovery after 3 hr. was measured directly and found to be 96%. In the same experiments the indirect method of Danielli et al. (1945) yielded varying results (89 and 109% recovery). 5. It is concluded that while rapid absorption of fatty acids from the rumen takes place at acid reactions, there is no absorption at all from alkaline solutions.