standard errors of the means of the ileal
digestibility values of crude protein and
amino acids when the inclusion level of
peas was increased from 168 to 504 g kg^1.
This shows that the accuracy of the deter-
mination of apparent ileal amino acid
digestibility values by the difference method
is dependent on the inclusion level of the
assay feed ingredient (peas) in the assay diet.
For estimating the apparent ileal
digestibility values of crude protein and
amino acids in the assay feed ingredient
(peas) by the regression method, the linear
relationships between the apparent ileal
digestibility values in the diets (diets 2, 3,
4 and 5) and the contribution levels of
crude protein and amino acids from the
basal feed ingredient (wheat) to the diets
were analysed according to Equation 13.11.
The regression equations are presented in
Table 13.9. However, linear relationships
were not significant (P> 0.05) for crude
protein, alanine, glycine, histidine,
threonine and valine (Table 13.8). This was
due to the fact that the differences in
apparent ileal digestibility values of crude
protein and these amino acids between the
assay (peas) and the basal feed ingredient
(wheat) were not large enough to create
linear variations. The principle for deter-
mining apparent ileal amino acid digesti-
bility values in the assay feed ingredient
(peas) by the regression method is illus-
trated in Fig. 13.7 with cysteine as an
example. The apparent ileal digestibility
values of the majority of the amino acids in
peas were determined by the regression
method according to Equations 13.12 and
13.13 (Table 13.10). On the other hand, the
presence of linear relationships for the
majority of amino acids between the assay
(peas) and the basal feed ingredient (wheat)300 W.C. Sauer et al.
Table 13.9.The linear relationships between the apparent ileal digestibility values and the contribution
levels of crude protein and amino acids for the determination of apparent ileal digestibility values of amino
acids in peas with the regression method (Fan and Sauer, 1995b).
Items Regression equationsa,b r^2 Sy. xc
Crude proteind Y= 74.9 + 2.9X 0.09 2.98
Amino acids
Indispensable
Arginined Y= 89.4 + 7.9X 0.46 1.95
Histidine Y= 79.9 + 0.9X 0.01 2.58
Isoleucined Y= 74.9 + 7.0X 0.23 3.68
Leucined Y= 74.8 + 8.0X 0.33 3.39
Lysined Y= 82.5 + 17.7X 0.65 2.51
Methionined Y= 64.9 + 14.6X 0.56 4.24
Phenylalanined Y= 76.2 + 7.9X 0.42 2.77
Threonine Y= 67.2 + 1.0X 0.01 4.11
Valine Y = 72.5 + 5.8X 0.14 4.12
Dispensable
Alanine Y= 70.1 + 2.1X 0.01 4.86
Aspartic acidd Y= 77.6 + 8.6X 0.23 3.61
Cysteined Y= 56.5 + 26.1X 0.85 3.53
Glutamic acidd Y= 83.9 + 7.3X 0.58 2.07
Glycine Y= 65.8 + 4.0X 0.03 6.71
Serined Y= 71.9 + 7.7X 0.42 3.45
Tyrosined Y= 69.0 + 7.2X 0.26 3.61
aY= apparent ileal digestibility values of cude protein or amino acids (%) in the assay diets.
bX= the contribution levels of crude protein or amino acids from the basal feed ingredient (wheat) to the
content of the assay diets.
cStandard error of estimate of the regression equation.
dThe linear regression equation is significant (P< 0.05, n= 20).