External marker concentrations overtime in cattle feces after pulse dosed with ytterbium

Two methods for fitting nonlinear compartmental, age-dependent digestion models: A comparison with empirical data. The objective of this research was to compare similar parameters generated by fitting the G2 and G2G1 models to fecal marker excretion datasets using published data from cattle given pulse doses of Yb using either SAS (Version 9.4; SAS Inst., Inc.) and R (R Core Team, 2017) software, and to compare the digesta kinetics estimates calculated with these different sets of parameters. We hypothesize that the model parameters and digesta kinetics estimates will not be different between the 2 software sources. Furthermore, we will characterize the bias and SD of differences between methods to determine whether these methods may be considered interchangeable.