Effects of a Stepwise Replacement of Hay with Corn Silage on pH, Some Organic Metabolites, and their Changes in the Rumen Fluid of the Bovine after Feeding1,2

Abstract

Feeding of acid preserved forages such as corn silage does not affect rumen fermentation adversely. A complete replacement of hay with corn silage in rations of equal dry matter intake did not change the average pH nor the total volatile fatty acids in the rumen fluid. The content of total volatile bases and the proportion of acetic acid of the total volatile fatty acids decreased; however the proportions of propionic, iso-valeric, n-valeric and n-caproic acids increased. Changing proportions of iso-butyric and n-butyric acids were nonsignificant. Hay and corn silage, offered combined but not blended at 2 different proportions, decreased pH and the proportion of propionic acid and increased the total volatile fatty acids in the rumen fluid. Significant changes with time after feeding were observed in all rumen fluid constituents. Significant hour × ration interactions occurred for total volatile bases, proportions of iso-butyric, n-butyric, isovaleric and n-valeric acids of the total volatile fatty acids.Prediction equations expressed changes as a function of time after feeding. Means of samples collected at 9 hourly intervals once a day were compared with means of samples taken at 3 hours after feeding.Results showed that knowledge of changes of a rumen constituent after feeding is essential for a correct interpretation of data from a single sample collected at a specified time after feeding.