Abstract:
Some reports indicate a wide range for Zn requireme
nts for broiler chickens i.e. from
10.6 to 105 mg kg
-1
. A number of factors other than dietary Zn concent
ration determine
the need for supplementation, principally dietary p
hytate. Therefore, the objective of the
present investigation was reevaluation of the zinc
requirement for broiler, fed practical diet
supplemented with phytase in a dose-response trial.
A total of 768 male Ross 308 broiler
chicks were used. Basal corn-soy diet deficient in
Zn was supplemented with experimental
diets for making 16 dietary treatments. Experimenta
l design was a completely randomized
design in a 4×4 factorial arrangement. Factors incl
uded four levels of dietary zinc (24, 54, 84
and 114 mg kg
-1
) and phytase (0, 100, 200, 300 FTU kg
-1
). Treatments were replicated four
times and each had 12 birds. Linear and nonlinear f
unctions were derived for graded levels
of zinc and phytase. Results indicated that effect
of dietary zinc on body weight at 42 days of
age was significant (P< 0.01). The fitted quadratic
model estimated 66.7, 64.8, and 60.1 mg
kg
-1
zinc requirement for body weight at 28, 35, and 42
days of age, respectively (P< 0.001),
while the fitted two slope broken line estimated 53
.5, 53.8 and 57.4 mg kg
-1
zinc requirement
for body weight at the same ages, respectively (P<
0.002). Zinc equivalence value of phytase
was estimated to be 0.225 mg kg
-1
FTU
-1
and added phytase increased liver zinc storage too
(P< 0.01). Estimated zinc requirement for body weig
ht by using practical high phytate diet,
low availability source of Zn, and exogenous phytas
e was lower than Ross 308
recommendation (60
vs
100 mg kg
-1
).
Keywords:
Broiler chickens,
Phytase, Practical diet, Requirement, Zinc
.
