Agriculture Reference
In-Depth Information
Ileal Digestibility of Amino Acids
As shown in Table 5, lysine and threonine are the least digestible essential amino acids in
wheat. The amino acids in high protein cultivars are more digestible than those in low protein
cultivars. This protein effect was particularly marked for the digestibility of lysine and
threonine, the two amino acids which are most likely to be deficient when chickens are fed
wheat-based diets.
Table 5. Apparent ileal digestibility of amino acids in wheat for broilers
1
Grain protein level, %
9
12
16
Indispensable amino acids
Arginine
0.79
0.81
0.81
Histidine
0.78
0.83
0.85
Isoleucine
0.83
0.86
0.88
Leucine
0.84
0.87
0.89
Lysine
0.76
0.77
0.80
Methionine
0.83
0.86
0.89
Phenylalanine
0.83
0.88
0.90
Threonine
0.68
0.74
0.78
Valine
0.80
0.83
0.85
Dispensable amino acids
Alanine
0.78
0.80
0.79
Aspartic acid
0.73
0.77
0.77
Glycine
0.77
0.81
0.82
Glutamic acid
0.93
0.95
0.95
Serine
0.80
0.83
0.84
Tyrosine
0.73
0.82
0.82
1
Ravindran
et al
. (1998; 2005).
A
NTI
-
NUTRITIONAL
E
FFECTS OF
N
ON
-
STARCH
P
OLYSACCHARIDES
It is believed that the NSP fraction (consisting mainly of arabinoxylans) is the major
contributing factor for the observed variability in wheat AME. Two key mechanisms have
been proposed to explain the effects of NSP (Bedford and Schulze, 1998). The first
mechanism is associated with the fact that starch and protein are encapsulated by the cell wall
in wheat endosperm cells. Cell wall composed mainly of cellulose, hemicelluloses (primarily
xyloglucans and glucuronarabinoxylans), pectins and lignin. It is noteworthy that most of the
arabinoxylans in cereal grains are insoluble in water because they are anchored to the cell
walls by alkali-labile ester-like cross links (Choct, 1997). Therefore, insoluble NSP can act as
a physical barrier to digestive enzymes. Since the endogenous enzymes in the birds are unable
to hydrolyse the cell wall, so the starch and the protein surrounded by cell wall may escape
digestion.
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