Relationships among rate of passage of feed, dry matter intake and chemical components of several diets

Abstract

Relationships among feed dry matter intake (DMI), rate of passage of feed through the rumen (ROP) and content of chemical components of feeds were determined to investigate the possibility of developing prediction equations for DMI and ruminal passage rates of digesta. ROP determined as exponential rate of marker decline in either feces (ROPf) or rumen contents (ROPr), DMI and body weight (BWt) of animals were determined using six mature steers in a 6 × 6 Latin square design experiment. Alfalfa hay (AA), orchard-grass hay (OG), alfalfa silage (AS), corn silage (CS), 70 + 30: cracked corn and OG (70G), and 70 + 30: barley straw and AA (70S) were used in the experiment. Chemical composition of feeds (protein, neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent insoluble nitrogen (ADIN) and lignin) was determined and, along with BWt of the steers, was regressed against DMI, while DMI was also included among the factors regressed against ROPf and ROPr. Even though animal factors, such as DMI and BWt, and feed factors, including the chemical components, were regressed against ROPf and ROPr, only protein and ADIN content in feed were significant factors included for ROPr (r2 = 0.358), while for ROPf, protein, ADIN and lignin content were the three significant factors (r2 = 0.362). However, DMI of the steers was predictable from the equation DMI (kg) = 15.52−0.080 NDF−0.101 ADF + 9.462 ADIN (as % of DM) (R = 0.84; P < 0.0001; residual standard deviation (rsd) = 1.01) with an R2 value of 0.702, but accurate estimation of rate of passage from feed and animal factors requires more research. Key words: Prediction of rate of passage, chromium mordanted neutral detergent fibre, intake, steers, forages