The research of both Nakashima and
Orskov (1989) and Beauchemin et al.
(1995) shows the potential value of pre-
processing feed with enzymes. Yet to ensile
or cube feed requires capital to be invested
possibly months before the feed is used.
The reliability of combining ensiling or
cubing with enzymes as a means of
improving animal performance requires
more research before the technique can be
relied upon. Unlike the pre-processing
approach, the addition of enzymes just
prior to feeding (also known as the direct-
fed approach) provides greater flexibility in
the use of forages and minimizes the time
and/or resources (silage bunker, etc.)
required.
Pre-processing of forage with feed
enzymes involves applying the enzyme
supplement well before feeding. Silage, for
example, is made by adding an inoculum
prior to sealing up of forage in a bunker or
wrapping round bales with plastic
(haylage). The first silage additive based on
enzymes alone appeared in the UK in 1985
(Treacher and Hunt, 1996). Improved
enzyme formulations produce well-
preserved silage, and around 75% of UK
silage additives for grass and maize now
contain enzymes. The enzyme activities
found in commercial additives do not
mimic the protein degradability of strained
rumen fluid (Luchini et al., 1996). This is
probably a good feature because it means
that feed enzyme activities are more likely
to be complementary rather than competi-
tive with endogenous enzyme activities.
By ensiling straw with a cellulase–
xylanase mixture, Nakashima and Orskov
(1989) improved the potential degrada-
bility of the straw by 10%. Beauchemin et
al. (1995) measured improvements in the
average daily gain (30%) and a 10%
increase in dry matter intake of steers
offered lucerne and timothy grass hay that
had been treated with enzymes during
the cubing process. It is encouraging to
see feed pre-processed with enzymes
improving ruminant growth. The economics
of this technique, however, must be
evaluated against application of enzymes at
feeding.
The application of enzymes at or just
prior to feeding is called direct-fed applica-
tion. If enzymes can be added to the forage
portion of the diet, at or just prior to
feeding, and produce improvements in
intake and digestibility, then the amount of
concentrate in the diet and the diet cost
can be reduced. Lewis et al. (1996) found
that direct application of a cellulase
and xylanase mix to the forage of a 70:30
grass hay:barley diet improved neutral
detergent fibre digestibility. Improvements
in digestibility have also resulted in
increases in production.
Schingoethe et al. (1999) measured a
10.8% increase in milk production, a 20%
increase in milk fat and a 13% increase in
milk protein as a result of adding a
cellulase and xylanase mixture at feeding.
Enzyme supplementation increased milk
production in the first 100 days of lactation
but not in mid-lactation. The improved
milk production was equivalent to provid-
ing the cows with a 45% forage:55% con-
centrate diet rather than the control diet
which contained 55% forage and 45%
concentrate. The simplicity of direct-fed
application of enzymes should see it
develop as the enzyme application
technique of choice for ruminants in the
future.Other factors influencing efficacy of feed
enzymes in ruminantsApart from the method of applying feed
enzymes, there are a number of factors
which influence the efficacy of feed
enzymes. These factors include diet
composition, microbial source of enzyme
activity, mixture of enzyme activities,
inclusion rate, heat stability, ambient
temperature at feeding and class of animal.
Obviously the ingredients in the diet
influence the feed enzyme activities
required to maximize improvement in
digestibility. Beauchemin et al. (1997)
measured the effect of two enzymes on the
growth of feedlot cattle given either maize
grain and maize silage or barley grain and
barley silage diets. The enzyme with higherFeed Enzymes 417