The Amounts of Short Chain Acids Formed during Rumen Fermentation

The concentration of acetic, propionic, and butyric acids in 3 bovine rumens was determined at various times after feeding either an all hay ration or one consisting largely of concentrates. Two trials were conducted on each ration. The concentration of each acid first increased and then decreased with time after feeding. The values obtained were fitted to turnover curves. Acetic acid disappeared from the rumen at the rate of 3.3% per hour and butyric acid at the rate of 2.7% per hour. The standard error was 0.3%. The disappearance rate of propionic acid on the high concentrate ration was 4.6% per hour versus 3.2% per hour on the hay ration. The rates for conversion of feed to short chain acids ranged from 28 to 84% per hour. Pooling data from the 4 trials, the mM of acids per 100 gm. of rumen liquid which were produced from 1 lb. of T.D.N. were, 0.24 to 0.67 acetic, 0.02 to 0.26 propionic, and 0.04 to 0.21 butyric (P .05). The average rumen in these trials was estimated to contain 70 kg. of liquid. Using these values, it was computed that the cow obtains 3 to 13% of its energy from short chain acids.