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Journal of Dairy Science Vol. 98 No. 9, 2015
UPDATING AND ASSESSING THE CNCPS FEED LIBRARY
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Therefore, the variation encompassed is what might be
expected if a user ran a simulation in the CNCPS using
feeds from the feed library with no information on ac-
tual feed chemistry. The mean, SD, and distribution for
the components considered in our analysis are in Table
4 and are similar to other reports where the same com-
ponents and feeds are presented (Kertz, 1998; Lanzas
et al., 2007a,b). Data rarely fit a normal distribution
and were more commonly represented by a loglogistic
distribution, similar to the findings of Lanzas et al.
(2007a,b). The data of some components were skewed
and were better represented by distributions, such as
the Beta, Pearson, or Weibull (Table 4). When data are
skewed, the mean and SD are less appropriate in de-
scribing centrality and dispersion of a population (Law
and Kelton, 2000). Outputs of deterministic models,
such as the CNCPS, represent an average (Lanzas et
al., 2007b); however, when input variation is accounted
for, the mean value may no longer represent the most
likely value. For example, in Figure 7A, the mean value
for ME allowable milk is 34.1 kg/d; however, the most
likely value based on frequency of occurrence is 36.3
kg/d. These types of considerations are particularly
important when conducting model evaluations, as stud-
ies rarely report adequate information to complete a
robust model simulation (Higgs et al., 2012, Pacheco
Figure 4.
Change in model output from a 1-SD increase in both the chemical components and digestion rates of carbohydrate and protein
fractions of feeds used in the reference diet. Items are ranked in order of importance. CB1 = starch; CB2 = soluble fiber; CB3 = digestible fiber;
PB1 = insoluble true protein.