difference method using barley as the basal
feed ingredient. However, Fan and Sauer
(1995a) showed that the ileal digestibility
values of amino acids in barley, calculated
by the direct method, were underesti-
mated. Therefore, the ileal digestibility val-
ues of amino acids in canola meal
determined by the difference method were
probably overestimated at the low inclu-
sion level of canola meal (244 g kg^1 ).
Furthermore, there were no differences (P
0.05) in the ileal digestibility values of
amino acids in canola meal between the
inclusion levels of 305 and 366 g kg^1 as
determined by the difference method. The
inclusion of barley was lower at the higher
inclusion levels of canola meal (305 and
366 g kg^1 ). Therefore, the overestimation
of ileal digestibility values of amino acids
in canola meal determined by the differ-
ence method was eliminated at the higher
inclusion levels (305 and 366 g kg^1 ).
There were decreases in the standard errors
of the means of ileal digestibility values of
amino acids when the inclusion level of
canola meal was increased from 244 to
366 g kg^1. This shows once more that the
accuracy of the difference method depends
on the inclusion level of the assay feed
ingredient (canola meal) in the assay diet.
The higher the inclusion level, the more
accurate the estimation of ileal digestibility
values of amino acids by the difference
method.
For estimating the apparent ileal
digestibility values of crude protein and
amino acids in canola meal by the regres-
sion method, the linear relationships
between apparent ileal digestibility values
(diets 2, 3, 4 and 5) and the contribution
levels of crude protein and amino acids
from the basal feed ingredient (barley) to the
diets were analysed according to the model
described in Equation 13.11. The regression
equations are presented in Table 13.7.
Unexpectedly, linear relationships could not296 W.C. Sauer et al.
Table 13.6.Determination of the apparent ileal digestibility values^1 (%) of crude protein and amino acids in
barley by the direct, the difference and the regression methods (Fan and Sauer, 1995a).
Methods of determinationItems Direct method Difference method^2 Regression method
No. of observations 5 5 20
Crude protein 56.6 ± 1.88 58.9 ± 3.36 57.7 ± 2.83
Amino acids
Indispensable
Arginine^3 64.7 ± 1.93 69.8 ± 3.15 68.4 ± 2.39
Histidine 69.5 ± 2.68 71.9 ± 3.56 70.5 ± 2.27
Isoleucine 61.1 ± 3.29 66.9 ± 4.80 —
Leucine 66.6 ± 2.80 70.3 ± 3.79 —
Lysine^3 54.1 ± 4.18 61.3 ± 4.93 59.3 ± 4.65
Phenylalanine 69.6 ± 3.41 72.1 ± 4.28 —
Threonine 53.3 ± 3.12a 62.4 ± 3.90b —
Valine 62.6 ± 2.96 67.2 ± 3.94 —
Dispensable
Alanine 48.8 ± 2.96a 57.3 ± 3.39b 53.9 ± 2.81b
Aspartic acid 50.5 ± 3.83a 62.1 ± 4.68b —
Glutamic acid 75.1 ± 2.52 73.9 ± 2.10 72.2 ± 2.89
Glycine 31.7 ± 3.41a 48.1 ± 5.64b 34.5 ± 5.08b
Serine 58.4 ± 3.19a 64.8 ± 2.67b —
Tyrosine^3 51.5 ± 3.88 61.2 ± 5.62 58.2 ± 3.43
(^1) Mean and standard error of the mean.
(^2) Digestibility values calculated from diet 4 (675 g kg (^1) inclusion of barley).
(^3) Means in the same row show a trend to increase (P< 0.10, by one-tailed Student’s t-test).
a,bMeans in the same row with different superscript letters differ (P< 0.05).