Importance of Considering Rate of Passage When Determining Energy Content of Forages for High Producing Animals

Importance of Considering Rate of Passage When Determining Energy Content of Forages for High Producing Animals

The objective of this study was to determine the effect of higher rates of passage and correspondingly lower rumen retention times on digestion of forages. One hundred and fifty samples of legumes, grasses and grass-legume mixtures were collected from farmer samples submitted to commercial forage testing laboratories and 32 samples of alfalfa at varying maturity were collected from research plots. In vitro digestions were performed for either 24 or 48 hours followed by neutral detergent analysis. Neither acid detergent fiber (ADF) nor neutral detergent fiber (NDF) predicted the standard 48-hour digestion very well (r² = -0.38 and B0.26, respectively). Similar results were noted for 24-hour digestion (r² = -0.48 and B0.47, respectively). While the correlation was high between 24- and 48-hour digestions (r² = 0.86), individual samples showed considerable variation. It is recommended that digestion kinetics be considered with determining energy availability for forages for higher producing animals.