Agriculture Reference
In-Depth Information
When the gut is exposed to health chal-
lenges, Thr requirement increases due to
higher mucin secretion (Bequette, 2003)
and stimulation of immune functions
( Corzo
et al
., 2007). Threonine require-
ments reported in the literature range be-
tween 5.33 mg/kg day and
56
mg/kg day
(Leveille and Fisher, 1960; Edwards
et al
.,
1997; Bae
et al
., 1999a; Nonis and Gous,
2008). In addition to immune challenges,
age, genotype, methodology and environment
factors may account for this variation. The
same dataset obtained in the Thr assays
carried out by Bonato
et al
. (2011) was also
used here to estimate requirements (
Table 15.3
quirement to obtain zero nitrogen body re-
tention was estimated as 17.1 mg/
BW
kg
day,
which is much lower than the minimum
maintenance requirement of
55
mg/
BW
kg
day
determined by Leveille
et al
. (1960) and of
56
mg/
BW
kg
day determined by Nonis and
Gous (2008). Possible explanations for this
result are the low health challenge pro-
moted by the metabolic-cage environment
and low abrasion caused by the experimen-
tal diets in the gut.
Valine is potentially limiting in corn
and soybean meal-based diets, which may
become evident at older ages when dietary
protein content decreases (Corzo
et al
.,
2004). Corn protein contains relatively low
valine and isoleucine and high leucine
levels (Corzo
et al
., 2004). The structure of
these amino acids is very similar; that is,
they are branched-chain amino acids (BCAAs)
and there is an antagonism between them
(Allen and Baker, 1972; Farran and Thomas,
1990; Bae
et al
., 1999b). This suggests that
maintenance requirements for Val are prob-
ably not constant and are influenced by its
ratio to the other BCAAs in the diet (Bae
et al
., 1999b). Therefore, leucine and iso-
leucine requirements should also be taken
into account when determining Val re-
quirements. Inadequate dietary Val impairs
body weight gain and feed conversion and
causes feather abnormalities in broilers
(Farran and Thomas, 1992). The valine
requirement obtained in the present
study is higher (46.1 mg/
BW
kg
day) than
the other evaluated amino acids. This may
be explained by the importance of main-
taining feather synthesis in adult roosters,
because the small weight changes (less
than 0.05) observed can be attributed to
water balance changes and to feather loss
(Leveille and Fisher, 1959). The Val re-
quirement determined here is consistent
with literature reports, although slightly
lower than the minimum maintenance re-
quirement of
55
mg/
BW
kg
day determined
by Leveille
et al
. (1960).
As mentioned above, it is difficult to
compare studies when different scales are
used to express maintenance requirements
for amino acids. Nonis and Gous (2008),
studying Lys and Thr and working with
the same methodology applied in the pre-
sent study, found higher Lys requirements
compared with other studies, and attrib-
uted this result to the fact that excreta
were collected directly from trays, because
the faeces in the trays below the cages are
exposed to nitrogen-rich feather residues.
However, the results of the present study
indicate that excreta collection technique
apparently had no influence on the esti-
mated requirements.
The objective of the experiments car-
ried out in the present study was to esti-
mate the maintenance requirements of
most essential amino acids in order to
apply effective models for the precision
feeding of chickens of different ages and
genotypes. These maintenance require-
ments may be used in factorial approaches
to determine general requirements, such
as the Reading Model (Fisher
et al
., 1973),
or to calculate the maintenance coeffi-
cients for broiler breeders (Bowmaker
and Gous, 1991). Emmans (1989) calcu-
lated amino acid requirements in ideal
protein for maintenance (PIM), where the
amino acid requirement, expressed per
BP
0.73
u
, is divided by eight (assuming
that roosters need
8
g of protein with ad-
equate composition to supply their main-
tenance requirements). From the results
of the studies reported here, the concen-
trations of Met+Cys, Thr, Lys and Val in
ideal body protein for maintenance are
10.9 g/kg, 5.59 g/kg, 10.7 g/kg and 27.4 g/kg,
respectively.
