Studies of the effects on the fermentation pattern in the rumen of the addition of various sources and levels of the lower volatile fatty acids

Abstract The short term effects on rumen fermentation of the direct addition to the rumen of 1·5 M and 3 M of acetate, propionate and butyrate, given as the Ca2+, Na+, and NH+4 salts and as the free acid were measured in a mature cow. Longer term effects of the oral addition of I·5 M of calcium and ammonium acetates were also measured in growing heifers. For all volatile fatty acids (VFA) each rate of addition consistently increased the level of VFA in rumen liquor, but these fell gradually over about 4 h. Total volatile fatty acids (TVFA) were lower when free acids were given than when their salts were used. There was little effect on rumen pH. Calcium acetate was unpalatable when offered orally, and it tended to depress TVFA levels. Mean effects of acetate salts given orally on molar percentage of acetate in rumen liquor were smaller than those found by direct addition.