Agriculture Reference
In-Depth Information
100
100
90
90
80
80
70
70
60
60
50
50
40
40
30
30
20
20
10
10
0
0
0
100
200
300
400
500
600
700
800
900
1000
Amino acid intake (mg/bird/day)
Fig. 19.1.
The relationships between amino acid intake and egg production and egg weight, where these are
expressed as a proportion of the maximum rate of lay and maximum egg weight, respectively. Lys (●), Met+Cys
(▲) and Thr (■).
acids studied, similar to the conclusion drawn
by Morris and Gous (1988). This again shows
the futility of reducing the amino acid supply
in an attempt to alter egg weight without redu-
cing the rate of laying.
The three response trials reported here
were conducted when the hens were produ-
cing their maximum egg output so the distri-
bution of egg outputs was close to a normal
distribution. At a later stage of lay, and in
most broiler breeder flocks, egg output is not
normally distributed, making conventional
statistical analyses difficult if not invalid
(Zhang and Coon, 1994; Morris, 2004).
The optimum economic amino acid in-
take decreased as the ratio of marginal cost
to marginal revenue increased (
Table 19.5
)
.
Egg producers should be aware that the op-
timum economic supply of essential nutri-
ents is not static but varies according to supply
and demand, hence the need to recalculate
this optimum whenever the cost:benefit
ratio changes. But the optimum economic
amino acid intakes were not only a function
of the cost ratio (
k
) but also of body weight
and potential egg output. As these variables
increase, so the rate of protein synthesis in-
creases and more amino acids are required.
Considering Lys as an example, for a hen
with a
55-
g potential egg output and a body
weight of 1.45 kg the optimum Lys intake
ranged from 730 to 771 mg/bird/day as a
function of
k
(
Table 19.5
)
and for a fixed
k
value of 0.0023, the current value in
Brazil, the optimum intakes ranged from
660 to 757 mg/day depending on mainten-
ance and potential egg output. This demon-
strates the wide range of intakes that could
be regarded as optimal depending on the
prevailing conditions and strain used. The
optimum intake of 771 mg Lys/day is never-
theless lower than that recommended in the
Brazilian Tables (Rostagno
et al
., 2011) for
laying hens weighing 1.5 kg and producing
55.5 g of egg output. However, the purpose
of this series of response trials was to de-
scribe the responses of laying hens to amino
acids and not to determine their 'requirement',
which is a concept that should not be ap-
plied to populations or flocks of laying hens.
The optimum intakes of the three amino
acids derived in this way are expressed in
mg/bird/day, but to formulate a feed it is ne-
cessary to know how much the hen is likely
to consume. Unfortunately, food intake does
not remain constant as the amino acid con-
centration is varied, so food intake needs to
be predicted before the amount of each amino
acid can be accurately supplied to the birds.
If an intake of
104
g were to be guaranteed,
and the mean body weight of the flock was
1.45 kg with a mean maximum egg output of
