Farm Animal Metabolism and Nutrition

be established (P> 0.05) for aspartic acid,
isoleucine, leucine, phenylalanine, serine,
threonine and valine. This was due to the
fact that the differences in apparent ileal
digestibility values for these amino acids
between the assay (canola meal) and the
basal feed ingredient (barley) were not large
enough to create linear variations (Table
13.7). The principle of estimating apparent
ileal amino acid digestibility values in the
assay feed ingredient (canola meal) by the
regression method is illustrated in Fig. 13.6
for arginine. The ileal digestibility values of
crude protein and some amino acids in
canola meal were estimated by the regres-
sion method according to Equations 13.12
and 13.13. The ileal digestibility values of
amino acids in canola meal estimated by the
regression method are presented in Table
13.8. However, as mentioned previously, the
ileal digestibility values of several amino
acids in canola meal could not be estimated
(Table 13.8).

The apparent ileal digestibility values

of crude protein and amino acids in canola

meal were determined by the direct

method (Equation 13.5) from diet 5, and

the digestibility values are presented in

Table 13.8.

As shown in Table 13.8, the apparent

ileal digestibility values of crude protein

and amino acids in canola meal estimated

by the regression method were not

different (P> 0.05) from those determined

by the direct method and were very close

to (P> 0.05) the values determined by the

difference method at the higher inclusion

levels of canola meal (305 and 366 g kg
^1 ).

These values were usually lower than

those determined by the difference method

at the low inclusion level of canola meal

(244 g kg
^1 ). These results show that the

regression and direct methods are valid for

determining the apparent ileal digestibility

values of amino acids in protein supple-

ments. With respect to the difference

Methods for Measuring Ileal Amino Acid Digestibility 297

Table 13.7.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 canola meal with the regression method (Fan and Sauer, 1995a).

Items Regression equationsa,b r^2 Sy. xc Pd

Crude proteine Y= 64.3 + 6.6X 0.52 3.39 0.001 0.05
Amino acids
Indispensable
Argininee Y= 79.5 + 11.1X 0.69 2.49 0.001 0.01
Histidinee Y= 78.7 + 8.2X 0.48 2.71 0.001 0.05
Isoleucine Y= 67.1 + 2.6X 0.01 3.81 0.001 0.66
Leucine Y= 69.1 + 1.5X 0.01 3.75 0.001 0.78
Lysinee Y= 71.8 + 12.5X 0.72 3.54 0.001 0.01
Phenylalanine Y= 69.2 + 0.6X 0.01 4.41 0.001 0.91
Threonine Y= 64.2 + 1.9X 0.01 3.68 0.001 0.52
Valine Y= 65.4 + 1.5X 0.01 3.94 0.001 0.79
Dispensable
Alaninee Y= 66.6 + 12.7X 0.74 4.04 0.001 0.05
Aspartic acid Y= 62.0 + 1.9X 0.01 3.75 0.001 0.75
Glutamic acide Y= 79.6 + 7.4X 0.55 3.02 0.001 0.03
Glycinee Y= 62.0 + 18.5X 0.76 5.51 0.001 0.01
Serine Y = 63.1 + 1.3X 0.01 3.45 0.001 0.79
Tyrosinee Y= 64.5 + 6.3X 0.54 3.54 0.001 0.04

aY= apparent ileal digestibility values of crude protein or amino acids (%) in the assay diets.
bX= the contribution levels of crude protein or amino acids from the basal feed ingredient (barley) to the

content of the assay diets.
cStandard error of estimate of the regression equation.
dThe probabilities of significance for the intercept and the slope of the regression equation.
eThe linear regression equation is significant (P< 0.05, n= 20).