All animals use enzymes to digest feed. These are either produced by the
animal itself, or by the microbes naturally present in the gut. However, the
animal’s digestive process is not 100% effi cient. Pigs and poultry cannot
digest 15–25% of the feed they eat, because the feed ingredients contain
indigestible anti-nutritional factors that interfere with the digestive process
and/or the animal lacks specifi c enzymes that break down certain components
in the feed.
In many animal production systems feed is the biggest single cost, and
on-farm profi tability can depend on the relative cost and nutritive value of the
feed ingredients available. If feeds are not digested by the animal as effi ciently
as they could be, there is a cost to both the producer and the environment.
Supplementing the feed with specifi c enzymes improves the nutritional
value of feed ingredients, increasing the effi ciency of digestion. Feed enzymes
help break down anti-nutritional factors (e.g. fi bre, phytate) that are present in
many feed ingredients. Anti-nutritional factors can interfere with normal
digestion, resulting in reduced meat or egg production and lower feed effi ciency,
and can also trigger digestive upsets. Feed enzymes are used to increase the
availability of starch, protein, amino acids and minerals such as phosphorus
and calcium from feed ingredients. In addition, they can be used to supplement
the enzymes produced by young animals where, because of an immature
digestive system, enzyme production may be inadequate. Enzymes are proteins
that are ultimately digested or excreted by the animal, leaving no residues in
meat or eggs.
The benefi ts of feed enzymes include:
• improving effi ciency and reducing cost – by breakdown of anti-nutrients
allowing the animal to digest its feed more effi ciently, leading to more
meat or eggs per kilogram of feed;
• for a better environment – improving digestion and absorption of
nutrients, reducing the volume of manure produced and lowering
phosphorus and nitrogen excretion;
• improving consistency – reducing the nutritional variation in feed
ingredients, resulting in more consistent feed for more uniform animal
growth and egg production; and
• helping to maintain gut health – by improving nutrient digestibility, fewer
nutrients are available in the animal’s gut for the potential growth of
disease-causing bacteria.
What Types of Enzymes are Used in Animal Nutrition?
Enzymes are categorized according to the substrates they act upon. Currently,
in animal nutrition the types of enzymes used are those that break down fi bre,
proteins, starch and phytate.
Carbohydrases
Carbohydrases break down carbohydrates into simpler sugars. In animal
nutrition they can be broadly categorized into those that target either nonstarch
polysaccharides (fi bre) or starch.
Fibre-degrading enzymes
All plant-derived feed ingredients contain fi bre. Fibre is made up of a number
of complex carbohydrates (non-starch polysaccharides) found in the cell walls
of plants. There are two main types of fi bre: soluble and insoluble. Fibre can
act as an anti-nutrient in a number of ways. First, some nutrients such as starch
and protein are trapped within the insoluble fi brous cell walls. Pigs and poultry
are unable to access these trapped nutrients as they do not produce the enzymes capable of digesting the fi bre within the cell walls. Secondly, soluble
fi bres dissolve in the bird’s or pig’s gut, forming viscous gels that trap nutrients
and slow down the rates of digestion and passage of feed through the gut.
Thirdly, fi bre can hold water and trap water-soluble nutrients. Finally, fi bre
creates bulk in the gut, which slows down the movement of feed, reducing feed
intake and subsequent growth.
The two main fi bre-degrading enzymes used in animal feed are xylanase
and β-glucanase. Xylanases break down arabinoxylans, particularly prevalent
in grains and their by-products. β-glucanases break down β-glucans that are
particularly prevalent in barley and oats and their by-products. Other fi bredegrading
enzymes currently used in animal nutrition, but to a lesser extent,
include β-mannanase, pectinase and α-galactosidase.
Starch-degrading enzymes
The degree of starch digestibility in plant-based feed ingredients will vary
according to the levels of resistant starch, starch granule size, starch composition
and starch encapsulation. Differences in plant genetics, growing conditions,
harvesting conditions, handling, drying, storage and feed manufacturing
processes are all likely contributors to variability in starch digestibility.
Amylases break down starch in grains, grain by-products and some
vegetable proteins. By increasing starch digestibility, amylases potentially allow
pigs and poultry to extract more energy from the feed, which can be effi ciently
converted into meat and egg production. In young pig diets, amylases provide
benefi ts by supplementing an immature digestive system where low feed intake
post-weaning is associated with a slow maturation of amylase secretion. In
addition, amylase also allows the use of less cooked grain in the diet, with
resultant benefi ts in feed cost reduction, without compromising young pig
performance after weaning.
Proteases
Proteases are protein-digesting enzymes that are used in pig and poultry
nutrition to break down storage proteins in various plant materials and
proteinaceous anti-nutrients in vegetable proteins.
Seeds, particularly of leguminous plants such as soy, contain high
concentrations of storage proteins. Storage proteins are proteins generated
mainly during seed production and stored in the seed to provide a nitrogen
source for the developing embryo during germination. Storage proteins can
bind to starch. Proteases can help break down storage proteins, releasing
bound energy-rich starch that can then be digested by the animal.
Two major proteinaceous anti-nutrients are trypsin inhibitors and lectins.
Trypsin inhibitors are found in raw vegetable proteins, such as soybeans. They
can inhibit digestion as they block the enzyme trypsin, which is secreted by the
pancreas and helps break down protein in the small intestine. Lectins are
sugar-binding proteins that have also been shown to reduce digestibility. While the trypsin inhibitors and lectins, excessive heat processing will reduce the
availability of amino acids, in particular lysine. Thus optimally processed
soybean meal will contain residual levels of trypsin inhibitors and lectins.
Proteases can be used to reduce the levels of trypsin inhibitors and lectins, thus
improving protein digestibility.
Phytases
Phosphorus is important for bone development and metabolic processes in
pigs and poultry. Most of the phosphorus in plant-derived ingredients is in the
form of phytate, which is the main storage form of phosphorus in plant seeds.
In the plant, phytate forms complexes with minerals (such as phosphorus and
calcium), proteins and starch, making them unavailable for absorption. Pigs
and poultry do not produce the phytase enzyme that breaks down phytate.
Supplementing the feed with phytase releases phytate-bound minerals,
proteins and starch, which can then be digested and absorbed by the animal
to improve the effi ciency of meat and egg production. Phytases also reduce
the risk of pollution of watercourses from excess phosphorus excreted by pigs
and poultry.