Agriculture Reference
In-Depth Information
the limiting amino acid intake as a percent-
age of
ND
max
T
. The proportions chosen of
the theoretical potential (40%, 50% and
60%) were within the range recommended
by Samadi and Liebert (2006b) to be close to
practical deposition values. These results
were transformed to obtain the optimal con-
tent in the diet (g/kg) according to a given
feed intake (g) and considering the recom-
mendations for the strain, although accurate
prediction of feed intake that may occur
under practical housing conditions is as yet
not possible (Samadi and Liebert, 2006b).
However, this modelling methodology allows
adjustment of the requirements according to
the situation because it is possible to adapt
the daily protein deposition and feed intake
to that observed in the field.
The values found in this study based on
50% of the maximum protein deposition
(
ND
max
T
), which was the mean value assessed
in this study, and the feed intake observed
in growth period I, are higher than the pre-
dicted values presented in the literature,
whereas the values for periods II and III are
lower, except for the values for lysine,
which were higher (NRC, 1994; Rostagno
et al
., 2011). This result is due to the pullets
depositing more protein in their bodies plus
their feathers during the first period of
growth (
6
to
12
weeks), with protein depos-
ition thereafter beginning to decrease. In
general, the values are lower than recom-
mended, which is due to the methodology
applied in this study (factorial model type
of approach), although the requirements are
consistent for pullets.
While characterizing threshold protein
deposition, Sakomura
et al
. (2012) obtained
a standard deposition rate (protein deposition
rate under normal conditions) and
PD
max
T
,
and found that pullets have a maximum
relative potential of 11% from
1
to 63 days,
meaning that they have a capacity for growth
that could be exploited by nutritionists. Ac-
cording to Sakomura
et al
. (2012) another
application of the knowledge of physio-
logical limits is the identification of the more
demanding individuals in the population,
which can facilitate the decision about the
ideal profile of amino acids to be included in
dietary protein.
In conclusion, the Goettingen approach
as applied in this study enables both the
daily amino acid requirements and optimal
in-feed contents to be estimated while con-
sidering the genetic growth potential of the
birds, the desired rate of protein deposition
and expected feed intake. Among the advan-
tages of this method are the simplicity of the
trials, the use of a small number of animals,
the lack of the necessity to slaughter them so
that they may be re-used, and its low cost. In
addition, it is also possible to estimate with
high accuracy the nitrogen requirement for
maintenance and deposition, and the effi-
ciency of utilization of amino acids using
this method. However, further studies should
be conducted to estimate the amino acid re-
quirements of pullets during their growth
period, due to the importance of this period
in the development of hens.
Acknowledgements
We are grateful for the support of the
Fundação de Amparo à Pesquisa do Estado
de São Paulo (FAPESP) and the Conselho
Nacional de Desenvolvimento Científico e
Tecnológico (CNPq).
References
Allen, L.R. and Hume, I.D. (2001) The maintenance nitrogen requirement of the Zebra Finch
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lysine) of tryptophan, threonine, isoleucine and valine for chicks during the second and third
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