Agriculture Reference
In-Depth Information
acids are not required to maintain the content
of water, fat or minerals in the body (Emmans
and Oldham, 1988) the scale mg/
BP
0.73
day,
which accounts for metabolic protein weight,
is the preferred scale for expressing mainten-
ance requirements for amino acids.
Leveille and Fisher (1959) proposed
that the requirements of an adult animal are
largely determined by the composition of the
synthesized tissue, and in the case of roosters,
by feather synthesis. It was shown that lysine,
threonine, methionine + cystine and valine fit
this hypothesis, although the valine require-
ment level is lower than its content in fea-
thers (Leveille and Fisher, 1958, 1959, 1960;
Leveille
et al
., 1960). Feathers are important
body structures that provide body insulation,
reduce energy maintenance requirements and
prevent skin abrasions and infections (Urdaneta-
Rincon and Leeson, 2004). Feather synthesis
evidently is not the only factor influencing
maintenance requirements of adult roosters,
but it is probably very important. Mainten-
ance requirements are also determined by the
replacement of endogenous body losses under
non-stressful conditions (Mitchell, 1962).
Methionine is an important donor of
methyl groups required for the biosyn-
thesis of many essential body compounds
(Baker, 1991) and it supplies cystine needs
(Graber and Baker, 1971). Cystine plays a
special role in keratin synthesis, and
therefore is related to feathering (Baker,
1991). Although some studies have con-
sidered only methionine requirements,
cystine must also be taken into account.
The presence of cystine in the diet (
42
mg/
kg day) reduced the methionine require-
ment for maintenance by approximately
0.20 (Leveille
et al
., 1960). In addition,
cystine supply helps to reduce endogen-
ous catabolism when the body searches
feather follicles for cystine, even to the ex-
tent of degrading other tissue proteins
(Mitchell, 1962). Therefore, both methio-
nine and cystine deficiencies may impair
feathering (Deschutter and Leeson, 1986)
because sulphur amino acid content is
higher in feathers when compared with
muscle protein. Estimates of the sulphur
amino acid requirement for maintenance
reported in the literature range between
6.62 and
142
mg/kg day (Leveille
et al
.,
1960; Owens
et al
., 1985; Kim
et al
., 1997b;
Edwards and Baker, 1999). This wide vari-
ation may be explained by differences in
methodologies, bird age and scale. Accord-
ing to Bonato
et al
. (2011), a single dataset
of Met+Cys results from experiments with
roosters belonging to different genotypes
was used
(Table 15.3,
15.4
and
Fig. 15.1
)
.
The estimated Met+Cys requirement of
18.9 mg/kg day obtained is consistent with the
minimum maintenance requirement deter-
mined by Leveille
et al
. (1960) of
15
mg/kg
day. The small difference may be attributed
to a relatively lower cystine content in the
experimental diet.
On the other hand, Lys maintenance re-
quirement is lower in adult roosters than in
growing chickens because Lys is directed
mainly to muscle accretion and not to feather
protein synthesis. According to Urdaneta-
Rincon and Leeson (2004), feathering is not
affected by dietary Lys levels. Dietary lysine
deficiencies are more likely to affect body
protein than feather development. Therefore,
it may be assumed that the largest fraction of
Lys maintenance requirement is caused by
endogenous protein losses in mature birds
(Jansmann
et al
., 2002). The Lys requirement
estimated in this study with Cobb roosters is
lower than that found in other studies
(Leveille and Fisher, 1958; Edwards
et al
.,
1999; Sakomura and Coon, 2003; Nonis and
Gous, 2008; Siqueira
et al
., 2011), which
ranged between
29
mg/kg day and
168
mg/kg
day. Although the Lys requirement esti-
mated in the present study was very low
(
20
mg/kg day) Leveille and Fisher (1958) ob-
tained a Lys requirement of
29
mg/kg day
and showed no further improvement in ni-
trogen retention at higher lysine intake
levels in roosters. Although Burroughs
et al
.
(1940) proposed that Lys was not essential
for the maintenance of nitrogen balance in
rats, Leveille and Fisher (1958) showed it to
be essential for adult roosters, as found in
the present study.
Threonine, as with Lys, is essential
for body protein deposition. However, the
maintenance requirement for Thr is mainly
used to maintain gut integrity (Ball
et al
.,
1999) and immunity (Corzo
et al
., 2007).
