The Farmers Mart Jun-Jul 2020 - Issue 69 | Page 15

• JUN/JUL 2020
LIVESTOCK 15
Fig 4 (Bedford M & Greiner R, 2010) Fig 5. r2 for ph 3.3 = 0.5114; r2 for pH 5.5 =
0.3712 (Bedford M & Greiner R, 2010)
Fig 6. (Qian H et al., 1997) Diet with 66µg of vit D
phytase units (FTU) . However, different
phytases have different activities
depending on pH (see Fig 4), and the
activity of the enzymes standardised at
pH 5.5 may not be the best predictor of
the biological activity (see Fig 5).
The enzyme activity measured at low
pH (2.5 – 3.5) has better correlation with
the biological performance in broilers
than the phytase activity at 5.5 and in this
case, increasing the particle size of the
feedstuff of low-phosphorus diets with
added phytase would keep the feed in
the proventriculus and gizzard longer and
release more phosphorus (Bedford M &
Greiner R, 2010).
Despite the importance of the
addition of microbial phytase for the
improvement on the utilization of
phosphorus in the diet, exogenous
phytase hydrolyses less than 35% of
dietary phytate in broiler feeds (Selle
PH & Ravindran V, 2007). The use of
low-phytate cultivars (high available
phosphorus) along with exogenous
phytase improves the performance of
the flock, allowing a reduction of total
phosphorus in the feed in the order of
23 - 28% and reduction of phosphorus
excreted (Huff WE, et al.1998).
The future on phytase research
is focused on including it at higher
concentration in the feed, discovery of
new phytase enzymes, combination of
phytase with other enzymes (amylase,
xylanase, …) and optimisation of Ca/P
ratios (Ravindran V, 2010)
Ratio Ca/P in the Diet
High Ca/P ratios in the feed have a negative
effect in the utilisation of phytate-P
by the broilers (Ballam et al., 1984). It
is thought that Ca binds with phytate,
making the complex Ca-phytate less
soluble and more resistant to the action
of phytase enzymes. The deposition
of minerals in the bone decreases with
high Ca/P ration; the influence of Ca/P is
greater when no exogenous phytase is
added into the ration (see Fig 6).
Addition of Vitamin D 3
Vitamin D 3
improves the absorption of P
in the intestine (Table 2) by activation of a
transport system different to the transport
of Ca in the intestine (Edwards, 1993) and
it is been proposed that vitamin D 3
also
activates phytases and phosphatases to
hydrolyse phytate (Biehl RR et al., 1995)
with an additive effect when both vitamin
D 3
and exogenous phytase enzymes are
incorporated in the feed (table 2 & Fig 7).
And as we saw with the addition of
phytase, the addition of vitamin D 3
also
improves the metabolic energy of the diet
(Table 3).
Addition of Citric Acid in the Feed
It has been observed that supplementation
of organic acids, especially citric acid
has a positive effect in the utilization of
phytate-P by the chickens (Boling SD, et al.,
1998). Citric acid is also a potent chelator, so
it would compete for Ca in the lumen of the
intestine and that would reduce the number
of phytate-Ca complexes, making phytate
more vulnerable to hydrolysis (Boling SD, et
al., 2000).
The effect of the addition of different
amounts of citric acid to the diet can
improve the weight gain (Fig 8) and the
minerals deposited in the bones using diets
deficient in phosphorus.
As mentioned before, citric acid binds Ca
but does not interfere with the availability of
Ca for the chickens in the intestine (Boling-
Frankenbach et al., 2001).
Despite these positive effects on the utilization
of phytate-P by the chickens with the
addition of citric acid, the use of this organic
acid in the diet at 4 – 6% is not economically
viable, (Boling SD, et al., 2000), so it should
be used in combination with the other
measures already discussed. See Fig 9.
Weight gain (g)
Tibia ash (g/100g)
Control 195 29.1
Control + 20 µg vit D/kg 235 40.9
Control + 1200 FTU/kg 245 38.5
Control + 20 µg/kg + 1200 FTU/kg 253 42.7
Table 2.(Biehl RR et al.,1995) Weight gain and tibia ash in chicks fed during 12 days with vit D or phytase or vit
D+phytase added to the control diet.
Control Diet Control Diet + 75 FTU Control Diet + 5mg vit D
Kcal ME 2883 2983 2993
Table 3 (Edwards HM Jr, 1993)
Conclusions
The addition of phytase in animal feeds
may release phosphorus for the absorption
in the intestine, increasing the energetic
value of the feed and the availability of
other nutrients such as amino acids and
minerals. The cleavage of phytate makes
more phosphorus available, improving
the deposition of minerals in the bone and
the growth of the flock, reducing the total
amount of phosphorus needed in the feed
and likewise reducing the excretion of
phosphorus to the environment.
The action of this enzyme can be potentiated
by the addition of vitamin D 3
and
organic acids.
For full list of references see article on
www.farmers-mart.co.uk.
Fig 7. (Edwards HM Jr, 1993). Bone ash with different
levels of phytase, with or without 10 cg vitamin D.
Fig 8. (Boling SD, et al., 2000). Weight gain in
chicks fed between the period 8 – 22 days old
Fig 9 (Snow et al., 2004). Diet 1: control; Diet 2:
control+3%citric acid; Diet 3: control+ 300FTU/kg; Diet 4:
control+10 µg vitD/kg; Diet 5: control+3%citric acid+300FTU/
kg+10 µg vitD/kg. Chicks fed between 8 – 22 days old