Agriculture Reference
In-Depth Information
Table 3.3.
Phytate concentration (g kg
−1
) and phytase activity
a
(FTU kg
−1
) in commonly used feedstuffs
(Eeckhout and De Paepe, 1994).
Feedstuff
Total P
Phytate P
Phytate P (% of total P)
Phytase activity
Wheat
3.3
2.2
67
1193
Barley
3.7
2.2
60
582
Triticale
3.7
2.5
67
1688
Rye
3.6
2.2
61
5130
Oat
3.6
2.1
59
42
Maize
2.8
1.9
68
15
Wheat bran
11.6
9.7
84
2957
Soybean meal
6.6
3.5
53
40
Rapeseed meal
11.2
4.0
36
16
a
One phytase unit (FTU) corresponds to the amount of enzyme that liberates 1
mol inorganic orthophosphate from
0.0051 mol l
−1
sodium phytate within 1 min at pH 5.5 and 37°C (Engelen
et al
., 1994).
μ
Similar to the replacement of crude pro-
tein by crystalline amino acids, inorganic
mineral phosphates (feed phosphates) have to
be re placed by the addition of microbial phytase
in order to improve the P efficiency. However,
the exchange rate of mineral phosphates has to
be adapted to the expected efficacy of microbial
phytase in the feed. This understanding is
important in order to avoid a too low P supply
(resulting in P deficiency) and at the same time
a surplus in P supply resulting in excessive
P excretion. Normally, the urinary P excretion is
very low but if the intake of digestible P is in
surplus of the animal's requirement, the sur-
plus is eliminated via urine. This combined
action of improved knowledge on digestible
P requirement, improved FCR and exchange of
feed phosphate by microbial phytase has gradu-
ally lowered the P excretion in grower-finisher
pigs (Fig. 3.9). From 1985 until 2012, the
P excretion per kg gain has been reduced 51%.
The biggest decrease was observed in the mid-
1990s and reflected the change in P recommen-
dation from total to digestible P and the onset of
microbial phytase supplementation. Recently,
an increase in P excretion has been observed
due to a slight increase in P recommendations.
Figure 3.10 shows the relationship between
P intake, P absorption, P retention and P excre-
tion in faeces and in urine in the grower-finisher
pig. At low P supply, the retention is low and the
urinary excretion is also very low reflecting the
inevitable loss. Increased P intake results in
increased P absorption and retention, and at a
certain P intake, the P retention reaches a pla-
teau. At the same time, the urinary P excretion
HO
Ca
OH
O
=
P-O
O-P
=
O
⊕
Zn
O
O
O
⊕
O
=
PO
H
H
⊕
H
O
Mg
O
⊕
O
=
P-O
O
H
O
H
O-P
=
O
⊕
O
Fe
H
O
⊕
O-P
=
O
OH
Fig. 3.8.
The phytate molecule (Ins P
6
; myo-
hexakisphosphate; Erdman, 1979).
The efficiency of phytase on the P digestibility
depends on the composition of the feed because
some cereals such as maize and heat-treated pro-
cessed oilseeds such as soybean meal do not pos-
sess plant phytase themselves, which is why the
effects of microbial phytase supplementation are
up to 0.8 g of digestible P per kg (Jongbloed, 2012).
In contrast, the effect of microbial phytase addition
may be about 50% less in feed containing wheat
and barley, as these cereals possess plant phytase.
Table 3.3 shows the plant phytase activities in
commonly used feedstuffs. However, when cereals
containing plant phytase activity are heat treated,
phytase may be partly inactivated affecting the
digestibility of phytate P. As such, it is very impor-
tant to be aware of the specific feeding conditions
when the digestibility of P is forecasted. Currently,
only a few feed optimization programmes include
appropriate preconditions to predict the accurate
content of digestible P in feed for pigs and poultry.
