Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/1996
Publication Date: N/A
Technical Abstract: Two models were used to predict intake of five switchgrass hays varying in maturity from vegetative to heading. The first model (M1) consisted of four compartments and required IVDMD, NDF, and CP as inputs. The second model (M2) consisted of 12 compartments and required analysis of three masticate particle size classes and the IVDMD and NDF of each class. Model predictions of rate of passage (ROP), rumen fill (fill), fecal output (FO) and DMI were compared to experimental observations of steers consuming the switchgrass (Panicum virgatum L.) hays. Observations indicated that, with increasing maturity, ROP declined from 3.25 to 2.14%/h, fill increased from 1.36 to 1.64%BW, FO decreased from .66 to .58%BW/d, and DMI decreased from 1.76 to 1.13%BW/d. If equal weight is given to all 4 variables, the simpler M1 outperformed the relatively complex M2. With the parameters of M2 adjusted for inadequate protein based on the results of the M1 simulations the results were better than either M1 or M2 alone. This approach yielded predictions that, with increasing maturity, ROP declined from 2.07 to 1.45% /h, fill increased from 1.89 to 2.02%BW, FO decreased from .80 to .65%BW/d, and DMI decreased from 2.46 to 1.38%BW/d. Correlations between observations and predictions were .91 (P=.030) for fill, .68 (P=.203) for FO, and .97 (P=.007) for DMI.