Agriculture Reference
In-Depth Information
dietary amino acid ratio: for the N balance
experiment a group of birds was utilized to
study the effects of dilution of individual
AAs on protein quality (Samadi and Lieb-
ert, 2008); simultaneously to this N balance
trial a group of birds was slaughtered at the
start and end of the experimental period to
provide the data needed to calculate a diet-
ary AA pattern, in which all the AAs were
equally limited, by a proposed broken line
model (Rollin
et al
., 2003).
Procedures
The N balance trials were divided into
adaptation period (5 days) and two consecu-
tive periods of excreta collection (5 days
each). During this period the experimental
diets were supplied until the end of excreta
collection. At the beginning of the adapta-
tion period diets were supplied
ad libitum
to predict the feed intake (according to
metabolic body weight) for the collection
period. The feed was supplied until the
beginning of the third day of the adaptation
period. Based on the measured consump-
tion of the last 3 days of adaptation the feed
supply was slightly adapted for the next
2 days. At the start of the collection period,
feed intake was measured again and the
feed supply for each individual was kept
constant to the end of the collecting period.
This procedure was suggested as an accept-
able adaptation to increasing feed intake in
fast-growing chickens (Samadi and Liebert,
2008). The excreta were collected directly
from trays (free of feathers) and immedi-
ately stored in a freezer at -20°C until fur-
ther analysis could be undertaken. Body N
deposition was also determined using the
comparative slaughter method. At the begin-
ning of the trial two birds of each replicate
with similar body weight were euthanized
using CO
2
after a fasting period of
36
h in
order to determine N content in the whole
body (carcass plus feathers), and at the end
of each assay all remaining birds were also
slaughtered. The slaughtered birds were
stored in a freezer at -20°C before further
processing.
Animals and housing
The experiments were carried out in the
Laboratory of Poultry Sciences of the Fac-
ulty of Agriculture and Veterinary Sciences,
Universidade Estadual Paulista, Jaboticabal,
São Paulo, Brazil. Within the age periods
the birds were randomly allocated to treat-
ments and individually housed in metabol-
ism cages with wire floors, equipped with
individual feeders and self-drinking systems.
The temperature was controlled using a
negative-pressure system, starting with 32°C
(
1-
day-old chicks) and decreased continu-
ously to 24°C by 53 days.
Experimental diets
A balanced diet (BD) was formulated accord-
ing to the recommendations of the Bra-
zilian tables for poultry and swine (Rostagno
et al
., 2011) for the ideal amount of pro-
tein for growing broilers for each period.
The N and AA content of the BD was sup-
plied by maize, soy protein concentrate and
a mixture of crystalline
l
l-AAs. Experimen-
tal diets with different limiting AAs were
created by dilution of the BD with maize
starch to achieve 0.70 of the AA level in
BD and supplemented with crystalline AAs,
except for the AA under study. In all experi-
mental diets the remaining nutrient and
energy contents remained the same. The
composition, AA and nutritional compos-
ition of the BD in each period is shown in
Chemical analysis
The excreta stored in the freezer were
thawed, homogenized and weighed. The
samples were then freeze-dried (Edwards
501, Thermo
®
, Crawley, West Sussex, UK)
at -90°C for
72
h. The dried samples were
ground in a micromill (A11 Basic, IKA
®
,
Staufen, Germany) and then stored in a
freezer (-20°C) until analysis. The initial
and final groups of slaughtered birds stored
