Relationships Between Efficiency of Milk Production and Ruminal Volatile Fatty Acids of Cows Fed Isocaloric (ENE) Rations of Varied Concentrate Levels

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Abstract
Increasing the level of concentrates from 30 to 90% of the dietary ENE (relative to hay) decreased the requirement, above maintenance, per pound of milk (4% fat-corrected) from 0.82 to 0.55 therms digestible energy (DE) and from 0.40 to 0.28 lb total digestible nutrients (TDN). As the percent of concentrates in the ration increased, total ruminal volatile fatty acids (VFA) decreased. The proportion of acetic acid decreased, butyric acid increased, and propionic acid was unaffected. The amount of TDN required for milk production was significantly correlated with concentrations of total ruminal VFA (+0.63), butyric and higher acids (-0.81) and the acetic-to-butyric acid ratio (+0.90). Correlations of VFA and the DE requirement for milk production were similar to those for TDN, but were smaller.