April 2013 - AFMA

How to overcome anti-nutritional
factors using a range of enzymes
By J-P Ruckebusch, DSM Nutritional Products Ltd, Kaiseraugst, Switserland; I. Knap,
DSM Nutritional Products, Village-Neuf, France & M Umar Faruk and E Upton Augustsson,
Novozymes A/S, Bagsvaerd, Denmark
Anti-nutritional factors (ANFs)
are substances generated
in natural feedstuffs by the
normal metabolism of plant
species (Kulmar, 1992). Cereal
grains and vegetable proteins are the
main ingredients used to meet the energy
and protein requirements in poultry and
swine diets. However, these ingredients all
contain varying levels of ANFs which interfere
with the optimal utilisation of dietary
nutrients. ANFs act by reducing protein digestibility,
binding to various nutrients, increasing
gut viscosity and thereby reducing
digestive efficiency (Lange, 2000).
There is a continuous effort to fully
characterise and understand the full impact
that ANFs have in feed, and also the
full impact that the removal of these factors
will have on animal production.
Exogenous feed enzymes
Exogenous feed enzymes have been used
in commercial diets for several decades
to increase the nutrient value of feed ingredients
by the targeted degrading or
modification of ANFs such as phytin and
non-starch polysaccharides (NSPs), and
more recently protease inhibitors and
lectin present in soybean meals – leading
to substantial cost savings in animal feed
formulations. The use of feed enzymes furthermore
does not only provide flexibility
in feed formulation, allowing for cheaper
raw materials to be used in animal diets,
but also improves the sustainability of livestock
production.
An enzyme can only be a valuable solution
if the substrate that it can degrade
is causing a problem, for example, an antinutritional
factor, or if the substrate is a nutrient
that is not utilised in the optimal way.
Commercially available products may contain
single (mono-component) enzymes,
a blend of several mono-components or a
cocktail of enzymes which contains guaranteed
levels of certain enzymes together
with unspecified enzymes’ so-called side
activities.
Phytic acid
The most well-known ANF in non-ruminant
nutrition is phytic acid, of which the
content in various feedstuffs as well as its
effect on phosphorous availability have
been well documented. It is also well documented
that the anti-nutritional effect of
phytic acid goes beyond that of reducing
phosphorus (P) and calcium (Ca) availability,
and its destruction leads to a lift in digestibility
of minerals, energy and amino
acids availability. The use of phytase is now
a standard practice in swine and poultry
diets.
The negative effects of non-starch polysaccharides
(NSPs) on digestibility and the
rate of absorption of nutrients from starch,
proteins and fats have been demonstrated
in several studies (Choct et al., 1992; Cowieson,
2005). The effect of NSPs on the availability
of nutrients is three-fold:
• Increasing of the gut viscosity.
• Reducing the flow of available nutrients
into the duodenum.
• Physically hindering the access of digestive
enzymes to nutrients enclosed
by the NSPs present in the plant cell
walls (cage effect).
Specifically in poultry, the NSP content of
cereal grain or vegetable protein and its
effects on both increasing the intestinal
viscosity as well as entrapping nutrients
by cage effect, have been shown to have
a negative effect on the nutritive value of
the feed. An increase in viscosity by the
soluble fibre fraction in plant cell walls,
such as arabino-xylans, beta-glucans and
pectinsis, is negatively associated with nutrient
availability. This is particularly true
for grains with a high level of soluble NSPs,
such as wheat and barley.
Effect of viscosity
The contribution of NSP’s degrading enzymes
on the effect of viscosity has been
measured in vitro. These in vitro results are
used in predictive models to estimate the
ME content of the grain as well as the contribution
of NSP’s degrading enzymes (or
carbohydrates). Recently a balance study
and growth studies on broilers receiving
a mono component endo-xylanase in
wheat-based diets confirmed significant
beneficial effects on the digestibility of dry
matter, protein, lipids, the feed conversion
ratio and the AME of diets. Viscosity alone
was reduced by an average 50% (Francesch
et al., 2012).
The effect of the insoluble NSP fraction
has, however, been more abstract and
makes it difficult to predict the value of the
entrapped nutrients (starch and protein)
within the starchy endoderm. It has been
shown that even small reductions in xylans
content of grains can result in improved
feed conversion and animal performance.
By puncturing the arabino-xylan cell
wall cages, the diet digestibility is increased
by either intact nutrient released from the
“cages” available for further enzymatic digestion,
or digestive enzymes could enter
and degrade the substrates within the cells.
Digests from stomach samples of piglets
showed the presence of intact plant cells
resulting in the contents of some cells escaping
digestion after feeding (Le et al.,
2013). It is a common misconception that
the feed grinding and pelleting process
opens all the cell walls of the endosperm or
the aleurone.
Feed science
AFMA MATRIX ● APRIL 2013 41