The Farmers Mart Jun-Jul 2020 - Issue 69 | Page 14

14 LIVESTOCK JUN/JUL 2020 • farmers-mart.co.uk
DIETARY PHYTATE IN BROILER
NUTRITION AND GROWTH
Joaquin Percebal-Morlanes, DVM, MSc, MRCVS
Diets containing 5 g of casein and different amounts of phytate (IP6) and phytase
(Poultry Veterinarian, Poultry Health Services, Sheriff Hutton branch)
PLANTS naturally store phosphorus in
the seeds in form of phytate. This molecule
(Fig 1) can be found in cereal grains,
legumes and oilseeds (Ravindran et al.,
1995) and form complexes in the seed with
proteins; later on, the action of phytase
enzymes breaks the molecule down
making the phosphorus available for the
development of the plant during germination
(Carla E. Hegeman et al., 2001).
Feeds for animals based on cereals
and legumes contain phytate of which
approximately 28.2% is phosphorus
(Ravindran V, 2010.
Fig 1. Myo-inositol hexakisphosphate
structure (Wikipedia, 2010)
Phytate in feeds not only interferes with
the absorption of phosphorus but this molecule
can bind proteins (Selle et al., 2000),
cations (Morris 1986) and form complexes
with starch (Thompson and Yoon, 1984),
lowering the availability of nutrients
present in the diet for the chickens.
Plant-based feedstuffs must be formulated
with more phosphorus available
to the animal from inorganic sources
such as mono- or dicalcium phosphate
that is 95- 98% available to the broiler,
adding cost to the production (Leeson
S & Summers J, 2001). In addition to this
problem, the undigested phosphorus in
the phytic acid is excreted and when the
manure is spread to agricultural land, it
may lead to contamination of the land if
the amount applied exceeds the amount
of phosphorus taken by the crops and
contamination of water due to high concentration
of phosphorus being lixiviated
(Pote et al., 1996).
Phosphorus is an important mineral for
the nutrition of broilers as it is necessary for
the formation and maintenance of bones,
metabolism and fertility (in the case of
broiler parent stock) and is a expensive
feed component in the broiler diet.
There are different strategies in order to
minimize the problems associated with the
phytic acid present in the plant seeds and
improve the utilisation of dietary protein,
energy, phosphorus and other minerals
by the broilers and reduce the excretion of
phosphorus:
• Low phytate crops
• Addition of microbial phytase enzyme
• Control of Ca/tP ratio in the feed
• Addition of additives (vitamin D, citric
acid)
Low Phytate Crops
There are mutations identified in some
cultivars (maize, barley, rice) that have
been selected for their low content of
phytate in the seeds. Two low-phytate
alleles have been identified (lpa1-1, lpa2-1);
the content of phosphorus in these lines
with the allele of low phytate content
(lpa) is the same as the non-mutants lines
but the amount of phytate-P is 50 – 95%
lower, with more inorganic Phosphorous
(Raboy V, et al., 2001).
Likewise, there are soybeans lowphytate
variants that contain approximately
45-65% inorganic phosphorus whereas the
non-mutants variants contain 10-15% inorganic
phosphorus (Wilcox RJ et al., 2000).
Fig 2. The effect of the phytase enzyme in the digestibility
of N is more evident when any of the amino acids is
supplied at suboptimal levels (Ravindran V, et al., 2001)
0.5 g IP6/0 FTU 0.5 g IP6/1000 FTU 1 g IP6/0 FTU 1 g IP6/1000 FTU
DM digestivility 0.5 g 0.73 0.37 0.74
TAA digestivility 0.92 0.96 0.89 0.93
TMN 0.21 0.7 0.02 0.54
Table 1 (Cowieson AJ, et al., 2006) DM: dry matter; TAA: total amino acid; TMN: true metabolizability of nitrogen.
Addition of Microbial
Phytase Enzymes
Chickens have some specific and
unspecific phytase activity mediated
by enteric phytase and phosphatase
enzymes respectively in the small intestine
but this enteric phytase activity is
insufficient to break down all the phytate
ingested in a typical diet based on soya
and corn. The addition of exogenous
phytase enzyme helps to make more
phytate-P available for the chickens and
reduce the negative effects that phytate
has on the utilization of minerals, proteins
and energy (Cowieson AJ, et al., 2006).
Effect of exogenous phytase on
protein and energy utilization
Phytate not only binds to dietary protein
(Selle et al., 2000) and starch (Thompson
and Yoon, 1984), making them less
available for chickens but also interacts
with enteric enzymes such as amylase
(Knuckles BE & Betschart AA 1987) and
proteases (Caldwell, 1992), provoking
more secretion of enzymes, mucins and
increasing losses of endogenous protein
(Pirgozliev V et al., 2005).
In addition to that, phytate makes
Na+ less available for the chicken in the
lumen of the intestine, interfering with
systems of transport of amino acids and
glucose, Na+-dependant in the intestinal
wall (Ravindran V, 2010). All these actions
lead to a decrease in the digestibility of
the dietary protein in the order of 9 – 14%
(Knuckles et al., 1989).
Depending on the amount of phytate
in the diet and phytase added, we may
expect different digestibility and retention
of amino acids (see table 1 & Fig 2),
minerals and energy.
Digestibility of dry matter and utilization
of the energy, amino acids, phytate-P
and minerals increase when phytase is
added to the diet (Fig 3)
There are different types of exogenous
phytases commercially available from
fungal (i.e..: Aspergillus niger, Aspergillus
ficuum) to bacterial (i.e.: Escherichia coli)
origin, being the phytases of bacterial
origin more efficient releasing phosphorus
form phytate (Augspurger RN , et
al.2010).
The products commercially available,
express the activity of the enzyme by
Fig 3. The effect of the phytase enzyme in the
apparent metabolizable energy in a lysine
deficient diet (Ravindran V, et al., 2001)