Agriculture Reference
In-Depth Information
this trial is in preparation for the task of
synthesizing lipoproteins in the yolk, with
the mature state being achieved at around
the 30th week of age. Although its contribution
to overall protein deposition is small, never-
theless there is a need to supply the bird
with additional protein during this phase of
growth.
The factorial model of Martin
et al
.
(1994) does not consider the loss of feathers
during growth or the development of the three
additional body components measured in
this trial, so the daily requirements for amino
acids predicted by that model were expected
to differ from the improved model proposed
here. Accounting for feather loss of 0.04 g/day,
which may be regarded as feather mainten-
ance, makes only a small addition to the
amino acid requirements initially, but the
cumulative effect (1st to the 13th week of
age) amounted to an additional 28% of
the Met+Cys requirements, but less for the
other amino acids because of their lower
concentrations in feathers. The accumu-
lated amount of each of the three amino
acids (Lys, Met+Cys and Thr) required by a
pullet from the 15th to 21st week of age was
913 mg/bird, 846 mg/bird and 586 mg/bird
when the model (M1) of Martin
et al
. (1994)
was used. These totals were increased to
1185 mg/bird, 1004 mg/bird and 757 mg/
bird, or 1.30, 1.19 and 1.29 times, when the
additional requirements for feather loss and
ovary, oviduct and liver growth (Model M2)
were added.
These results suggest that the amount of
each of the three amino acids required to re-
place lost feathers and to ensure the success-
ful development of the reproductive organs
is not insubstantial and therefore should be
included together with the requirements for
the growth of feather and non-feather body
protein when calculating the daily amino
acid requirements of pullets during growth.
By ignoring the daily amounts of amino
acids needed to support the growth of these
additional components the predicted supply
of amino acids required in the weeks prior to
the onset of lay will be insufficient to meet
the needs of the developing pullet.
The results presented are based on the
suggestions of Emmans (1989) and Gous
et al
. (1999) that in order to determine the
amount of each amino acid that a growing
bird would need to consume in order to
grow to its potential, a complete description
is required of its growth potential. Though
the daily requirements calculated in this
study for Lys, Met+Cys and Thr are specific
to the current Dekalb White hens, the ap-
proach used here may successfully be used
for other laying strains.
Acknowledgements
The authors thank Fundação de Amparo à
Pesquisa do Estado de São Paulo (FAPESP)
for funding this study.
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