Despite this two-pronged approach to
digestion, some feed compounds are still
not well utilized.
Poor digestion of solid feed by piglets
weaned at 21–28 days of age is especially
obvious in the first 2–3 weeks after wean-
ing (Cera et al., 1988). Inappropriate choice
of feed ingredients at this time can produce
diarrhoea, due in part to a lack of
pancreatic and intestinal enzyme activity
and/or by the colonization by entero-
toxigenic coli bacteria (Cera et al., 1988).
The lack of pancreatic and intestinal
enzyme activity results in more nutrients
passing through the digestive system rather
than being absorbed by it. These nutrients
provide the substrate for pathogenic
bacteria such as Escherichia coli which
produce enterotoxins (affecting the entero-
cyctes in the wall of the intestine). These
in turn increase intestinal secretions and
further reduce digestion and absorption.
Removal of dietary ingredients which may
produce diarrhoea or hypersensitivity
reactions often means providing diets with
minimal vegetable protein meals and
cereals which are low in fibre and are more
expensive. Supplementation with feed
enzymes has the potential to increase the
use of vegetable protein meals and high-
fibre cereals and reduce diet cost without
compromising piglet health.
Typical endogenous protease and
amylase activity levels in piglets suggest
that supplementation should not be
required except for a short period
(1–2 weeks) immediately post-weaning
(Lindemann et al., 1986; Owsley et al.,
1986). This was confirmed by Cromwell et
al. (1988), who showed that an amylase–
protease combination was effective in
improving piglet performance but not
when the pigs were older or with protease
alone.
The results of enzyme addition to pigs
have been highly variable, with many
weaner pig enzyme trials failing to demon-
strate any benefit in terms of health or
increased production. For example, a
literature survey revealed that of 23
enzyme supplements for which growth
trials were conducted between 1978 and
1993, only four improved growth rate of
piglets (Officer, 1995). In growing–finishing
pigs, the growth-promoting effect of NSP-
degrading enzymes supplemented to cereal
diets has also not been established with
certainty (Chu et al., 1998).
Soluble NSP does not appear to
depress pig performance as it does in birds.
Thacker et al. (1988) showed no improve-
ment in weight gain intake or feed conver-
sion of 20 kg pigs (given a hull-less barley
high in soluble glucan). This was despite
recording significant increases in dry
matter and protein digestibility in pigs given
the diet supplemented with -glucanase.
Unlike in birds, pentosans do not appear to
be a significant cause of reduced perform-
ance in young pigs. Pentosanase supple-
mentation of a rye-based diet given
to 20–25 kg pigs (Thacker et al., 1991)
failed to significantly improve growth.
Supplementation with -glucanase in 80 kg
pigs tended to improve dry matter and
protein digestibility, but these changes
were thought to be too small to improve
weight gain or FCR.
In recent years, the most significant
development in feed enzyme technology
has been the release of phytase. Research
with phytase (1000 U kg^1 diet) has shown
that it increases P digestibility by 36–55%
in maize–soybean and by 54–68% in wheat–
soybean diets given to 5-week-old weaner
pigs (Eeckhout et al., 1992a). Jongbloed
(1997) also states that no inorganic P is
required in phytase-supplemented diets for
grower–finisher pigs and pregnant sows.
The benefits from adding phytase are
significant in terms of reducing diet cost,
improving mineral retention and animal
performance, but unfortunately recom-
mendations for phytase supplementation
vary with class of pig and diet (Yi et al.,
1996). There is no standard level of
phytase supplementation for all diets
because the total and phytate P level of
each diet varies.
These two experiments show how the
P equivalence of phytase is dependent
upon the diet. Yi et al. (1996) found that
the amount of phytase required to release
1 g of phytate P varied from 785 U, for aFeed Enzymes 413