xylanase activity improved the FCR of
cattle given the barley diets but not of
those given maize. Beauchemin and Rode
(1996) measured increased daily gain (6%)
and feed DM:gain (11%) of cattle with an
enzyme supplement containing a high
xylanase:low cellulase ratio. No benefits
were obtained by cattle given a low
xylanase:high cellulase supplement. These
results show the importance of having the
correct balance of enzyme activity based on
diet composition.
Not all enzyme combinations produce
benefits for the enzyme-supplemented
animal; some can have a negative effect on
growth or feed conversion efficiency
(Treacher and Hunt, 1996). Treacher and
Hunt (1996) tested a range of cellulase and
xylanase enzyme products and suggested
that more work was required to identify
useful combinations of enzymes for diets
based on various crop products. Ruminants
have bacteria that produce phytase activity
(Yanke, 1998). Further research is required
to determine if feed phytase has any
potential in ruminant diets.
Not only the type of forage, but also
the stage of maturity at harvest can
influence the optimum enzyme concentra-
tion required to improve animal perform-
ance. Michal et al. (1996) showed that
when the neutral detergent fibre content of
lucerne haylage increased from 415 to
540 g kg^1 , the optimum enzyme (cellulase/
xylanase) dose rate increased from 2.5 l t^1
to 5.0 l t^1. Therefore, it is important to
know not only the concentration of fibre in
each batch of feed but also other factors
such as feed pH which may influence the
activity of enzymes when added to feed.
The concentration of enzymes added
to the diet can be critical to maximiz-
ing improvement in animal performance.
Treacher and Hunt (1996) showed that dairy
cows given 5 l t^1 of enzyme-treated maize
silage–lucerne hay (80:20) produce less milk
than cows given a control diet. Yet cows
given 2 l t^1 of enzymes produced 6.8%
more milk and 7.8% more protein. Sanchez
et al. (1996) also showed improvements in
milk yield at 2.5 l t^1 of cellulose/xylanase
enzyme but not at 1.25 or 5.0 l t^1.
Treacher and Hunt (1996) suggested
three possible explanations for reduced
animal performance with excessive addi-
tion of enzymes. Firstly, it is possible that
high doses of enzymes reduce the amount
of neutral detergent fibre available for
fermentation by rumen microorganisms
which in turn reduces microbial protein
and VFA production. Secondly, the
presence of bound enzymes restricts the
access of microorganisms to the feed.
Thirdly, it is possible that enzymes release
anti-nutritional by-products (e.g. phenols)
which inhibit microbial growth.
Not only the rumen environment
but also the external environment can
influence how well feed enzymes work. It
is well known in enzyme chemistry that
interactions with a substrate are influenced
by temperature. Treacher et al. (1996)
showed there is a 1.5–2.0% increase in gas
production per 10°C (from 30 to 30°C)
from enzyme-treated barley silage. This
result may suggest problems with the
effectiveness of feed enzymes in the cooler
parts of the USA, Canada and Europe, but
benefits for subtropical countries.
Little is known of the differences
between various classes of stock in their
response to feed enzymes, but Beauchemin
and Rode (1996) showed that heifers were
more responsive to enzyme addition than
steers. More research is required to deter-
mine if gender, age or physiological state
influence the ability of feed enzymes to
improve ruminant diet digestibility.
In short:● Our understanding of the mode of
action of enzymes in ruminants is poor.
As a result, there is as yet no proven and
reliable means of direct application of
enzymes to ruminant feed. Despite this,
some experiments have shown carbo-
hydrase feed enzymes have the potential
to improve ruminant production.
● Recommendations on the period between
feed application and consumption and
general recommendations on optimum
concentrations of enzymes for different
diets are also not yet available.
● Further research should prove valuable
because there is considerable potential418 D.I. Officer