Agriculture Reference
In-Depth Information
diet, together with
ad libitum
supply of a
nitrogen-free diet, in order to ensure that the
other nutrients are not limiting. This method,
according to Burnham and Gous (1992), offers
the advantage of precisely measuring in-
take, preventing the feed refusal and waste
sometimes observed when test diets are
supplied in the feeder.
Bird age also affects the determination of
amino acid maintenance requirements. Stud-
ies have been carried out with growing chick-
ens (Kim
et al
., 1997a,b,c; Bae
et al
., 1999a,b;
Edwards and Baker, 1999; Sakomura and
Coon, 2003; Samadi and Liebert, 2006a,b,
2007a), mature laying chickens (layers or
broiler breeders hens) (McDonald and Morris,
1975; Bowmaker and Gous, 1991) and roosters
(Leveille and Fisher, 1958, 1959, 1960; Leveille
et al
., 1960; Gous
et al
., 1984; Gous, 1986;
Burnham and Gous, 1992; Nonis and Gous,
2008; Bonato
et al
., 2011). The degree of ma-
turity of a bird should be considered when
estimating maintenance requirements since
it can represent a larger or smaller proportion
of these requirements. Maintenance require-
ments increase proportionally as the bird ma-
tures; upon reaching maturity, it stops grow-
ing. For instance, growing birds such as
broilers have lower maintenance require-
ments as compared to mature birds, such as
layers or roosters, but have requirements for
growth. It is difficult to estimate the main-
tenance requirements of growing birds be-
cause their weight and body composition
change daily. On the other hand, in mature
birds, maintenance represents most of their re-
quirements. Therefore, it is more useful to meas-
ure maintenance requirements in mature birds
than in growing broilers. Maintenance re-
quirements should not be measured using
laying hens because it is difficult to separate
this requirement from that for egg produc-
tion, so it is better to use mature male chick-
ens to determine maintenance requirements.
According to Emmans and Oldham
(1988), several issues need to be considered
when determining maintenance require-
ments: genotypes differ in size at maturity,
and birds of the same genotype differ in
their requirements at different stages of
growth. One further problem is how to deal
with changes in body fat content, since there
is no requirement for amino acids for the
maintenance of lipid reserves.
Maintenance requirements have variously
been scaled to body weight of the fasting
bird (mg/
BW
kg
day) (Fisher, 1994), to meta-
bolic body weight (mg/
BW
k
0.75
day) (Hurwitz
et al
., 1978; King, 2001 and others) and to
feather-free body protein weight scaled to
mature body protein (Emmans and Fisher,
1986). The latter authors, based on the work
of Brody (1945) and Taylor and Young
(1968), showed that amino acid requirements
for maintenance are more closely related to
body protein content, because there is no
demand for amino acids for the mainten-
ance of lipid reserves. These authors pro-
posed the following equation:
MP
= (0.008 ×
BP
0.73
) ×
u
; where
MP
is maintenance protein
requirement (g/day); 0.008 is a constant (kilo-
grammes of ideal protein/maintenance unit),
which assumes that chickens require
8
g
protein with adequate composition (ideal) to
meet their maintenance requirements;
BP
m
is
body protein weight at maturity (kg); and
u
is the degree of maturity at time
t
(
u
=
BP
t
/
B-
P
m
=
1
in adult birds, and therefore,
BP
t
=
BP
m
).
Several studies have been conducted at
the Poultry Science Laboratory of UNESP-
Jaboticabal, Brazil, to evaluate the problems
and factors discussed above. This chapter
describes the methodology and the results
obtained in the determination of amino acid
requirements of chickens for maintenance.
Materials and Methods
Seven metabolism assays were performed
at the Poultry Science Laboratory of the Fac-
ulty of Agriculture and Veterinary Sciences,
UNESP-Jaboticabal, São Paulo, Brazil, to de-
termine the methionine + cystine (Met+Cys),
threonine (Thr), lysine (Lys) and valine (Val)
requirements for maintenance of adult roosters
using the methodology described by Nonis
and Gous (2008). Two assays were per-
formed for Met+Cys and three for Thr. Also,
assays were carried out to compare the
maintenance requirements for each amino
acid between Cobb (meat type) and Bovans
White (egg type) roosters in order to determine
if these requirements should be expressed
