Farm Animal Metabolism and Nutrition

reduced the gastrointestinal pH to an
optimum which better suited the microbial
phytase, allowing more P to be released.
In summary:

● Phytase addition allows the release of
plant P that is not otherwise available to
the animal. Phytase may also release
other minerals and protein bound to
phytate in compounds called phytate
complexes. Phytase addition reduces
the need for inorganic P supplementa-
tion, and in turn reduces the P content
excreted by animals.
● The amount of P released by a given
amount of phytase is affected by diet
composition.
● Some cereals including barley, triticale,
rye, wheat and wheat by-products have
significant inherent phytase activity.
Heat treatment of vegetable proteins
deactivates inherent phytase activity.
Inherent phytase activity increases the
availability of P in the plant source in
which it is contained but has no effect
on other ingredients in the diet.
● The choice of phytase source either as a
feed supplement, in feedstuffs with high
intrinsic phytase or combinations of
these sources with or without additional
products such as organic acid will be
made on the P-releasing capacity and
price of each competing source.

Role of proteases

Many vegetable protein sources such as
soybean contain protease inhibitors, lectins
and tannins which reduce animal perform-
ance. To remove the anti-nutritive effects of
these compounds, legume seed is heat
treated. Unfortunately heat treatment can
reduce the availability of amino acids.
As an alternative to heat treatment,
enzymes have proved partially successful
in deactivating anti-nutritional factors in
legume seed (Bohme, 1997). For example,
the addition of a protease to non-heat-
treated canola meal improved broiler chick
growth (Simbaya et al., 1996). Yet, it is in
combination with other enzyme activities
where proteases have been most successful.

The inclusion of a protease in multi-

enzyme supplements has proven beneficial

for chicks (Ranade and Rajmane, 1992;

Morgan and Bedford, 1995; Simbaya et al.,

1996) and layer egg yield and for piglet

gain and FCR (Adams, 1989). Not all

experiments have shown improved

performance with proteases (Officer, 1995).

In Officer (1995), two protease containing

multienzyme supplements failed to

improve piglet performance. It appears that

both the type of protease and the comple-

mentary enzyme activities in the multi-

enzyme supplement influence digestibility.

Antigenic effects of soybean on piglets

are not always removed with heat treat-

ment. Rooke et al. (1998) added an acid pH

protease to soybean meal and improved

piglet growth in the 7 days immediately

post-weaning. No reduction in soybean-

specific antibodies was observed for the

acid protease-supplemented pigs. This

experiment was brief in duration and there

was no evidence of soybean having an anti-

genic effect on any of the treatments.

The fact that proteases improve

performance in some circumstances is

remarkable. Except for the period

immediately post-weaning, ileal digesti-

bility of protein is high as a result of

endogenous protease activity.

Two points are worth noting:

● Multienzyme supplements containing

protease have proven beneficial in both

pigs and poultry.

● There is potential for further research

into protease supplementation of non-

heat-treated legume seed.

Feed enzymes are added to diets of

many of the animal species we farm. The

effectiveness of various types of enzymes is

discussed for poultry, pigs and some aqua-

culture and ruminant animals.

Enzyme Supplementation of

Poultry Diets

Broilers

More than any other animal industry, it has

been the broiler industry which has most

Feed Enzymes 409