Agriculture Reference
In-Depth Information
quality (e.g. L1, L2, L3, L4 and L5). In trial
two (T2) Lys was the limiting amino acid in
the diets; in trial three (T3) Met was limit-
ing; and in trial four (T4) Thr was limiting
(
Table 20.1
and
Table 20.2
)
. Each trial in-
cluded a control treatment in which a small
amount of the amino acid under investiga-
tion was added to a diet with the same com-
position as the diet with the lowest content
of the test amino acid to verify that the
amino acid under test was first limiting in
each trial.
Diets were formulated using the prin-
ciples of the diet dilution technique (Fisher
and Morris, 1970) according to the require-
ments of Rostagno
et al
. (2005).
Table 20.2
presents the amino acid contents relative to
crude protein and the ratio to the lysine con-
tent for each series of diets containing the
various limiting amino acids. The treatments
were the same in each study period.
metabolic cage conditions. Based on their
ad libitum
feed intake, the birds received
a controlled quantity of feed for the next
3 days. This procedure was followed for
the collection period. In the collection
period, the excreta were collected once a day
(in the afternoon) and immediately frozen at
-20°C for later analysis. The amounts of
feed intake (FI, g) and total excreta collected
were quantified.
Excreta were freeze-dried for
72
h
under controlled conditions (-80°C; -
80
kPa;
SuperModulyo; Thermo Fisher). Dry matter
content was determined using a forced air
oven at 105°C for
24
h, and the nitrogen
content of the diets and excreta was quanti-
fied using the Kjeldahl method (AOAC,
1990: method 2001.11, Kjeltec 8400; Foss).
To determine the amino acid composition
of the diets the samples were hydrolysed
with
6
M HCl under nitrogen for
24
h. The
amino acids released by acid hydrolysis
were separated using reversed-phase high
performance liquid chromatography (HPLC)
and detected in the UV range at
254
nm.
Nitrogen intake (
NI
, mg/BW
k
0.67
/day)
and nitrogen excretion (
NEX
, mg/BW
k
0.67
/
day) were determined. The nitrogen balance
(
NB
, mg/BW
k
0.67
/day) was calculated from
the difference between the
NI
and
NEX
,
respectively.
Experimental procedures
Each experimental period was divided into
an adaptation period (5 days) and a period
with total excreta collection (10 days). For
the first 2 days of the adaptation period,
the feed was available
ad libitum
to deter-
mine the optimal feed intake under the
Table 20.2.
Amino acid content of dietary protein (g amino acid/
100
g crude protein (CP)) and ratio to
lysine (%) in the diets limiting in different amino acids.
Lysine
trial (T2)
Methionine
trial (T3)
Threonine
trial (T4)
L1 to L5
(g/
100
g CP)
AA ratio to
b
Lys (%)
L1 to L5
(g/
100
g CP)
AA ratio to
c
Lys (%)
L1 to L5
(g/
100
g CP)
AA ratio to
d
Lys (%)
Amino acid
a
Lysine
4.95
100
5.82
100
5.37
100
Methionine + cysteine
4.05
82
3.52
60
3.92
73
Methionine
2.56
52
2.04
35
2.69
50
Threonine
3.80
77
3.79
65
2.95
55
Tryptophan
1.04
21
1.04
18
0.98
18
Arginine
6.28
127
6.26
108
5.74
107
Valine
4.62
93
4.58
79
4.13
77
Isoleucine
4.34
88
4.31
74
3.76
70
Leucine
10.0
202
9.86
170
10.6
198
a
Amino acid content determined in the feed.
b,c,d
Ratio of the amino acid relative to lysine (100%).
CP = Crude Protein
