Concentrations of Volatile Fatty Acids and Lactic Acid in the Rumen as Influenced by Diet and Post-Feeding Time

Abstract

The rations described were fed to rumen-fistulated steers for a period of 3 weeks prior to sampling. The concentrates were all fed as 80% of the diet with 20% alfalfa hay. On the sampling day one-half the daily ration was fed, and samples of rumen fluid collected for lactic acid and volatile fatty acid (VFA) analyses at 10 min. intervals after the start of feeding. The rations, the maximum lactate concentration (mg/100), the time after feeding for the maxima, and the acetic -propionic ratios respectively were; alfalfa hay, 3.0 to 5.0 over a 3 hr. period 4.0; pelleted dehydrated alfalfa, 25.5 at 50 min. 3.0; rolled barley, 22.0 at 50 min. 2.1; ground milo, 15.5 at 40 min. 4.4; dried beet pulp, 73.0 at 100 min. 4.8; flaked corn, 17.9 at 50 min. 1.2; flaked corn plus silage, 26.5 at 30 min. 2.8; and cracked corn plus silage, 58.9 at 40 min. 3.1. Lactate concentrations returned to pre-feeding levels in approximately the same time as required to reach the maximum. Comparisons failed to reveal any pattern which could be interpreted specifically as conversion of lactate to individual VFA at various times after feeding. Infusion into the rumen of 200 gm. of neutralized lactic acid resulted in high negative correlations between ruminal lactate and both propionate and butyrate.