Enzyme Supplementation of
Ruminant Diets
Feed enzymes, although part of many
bacteria-based silage starters, are not
widely used as direct-fed additives in
ruminant diets (Beauchemin and Rode,
1996). Research with feed enzymes in
ruminant diets has found them to be
unreliable (Leatherwood et al., 1960; Perry
et al., 1966; Adoglabessa and Owen, 1995)
and, until recently, the cost of development
and production of enzymes for ruminants
was prohibitive. Improvements in recom-
binant DNA technology (Selinger et al.,
1996) and research with monogastric
animals should see the development and
release of direct-fed enzyme products
specifically for ruminants.
Part of the slow uptake of enzyme
technology by ruminant feed manufacturers
is due to the fact there is no simple foolproof
recipe for applying enzymes and securing a
profitable response. A lack of understanding
in the way enzymes act in ruminant feed
and the complex digestive tract of ruminants
means that there are many unidentified or
misunderstood factors influencing feed
enzyme efficacy in ruminant animals.
Enzyme supplementation in ruminants
may be complex, but this should not deter
investment in research and development.
Improvements in the efficiency of feed
utilization as the result of feed enzymes
will increase production profitability and
waste minimization in a large, and as yet
relatively untapped, ruminant feed enzyme
market.
Like monogastrics, ruminants can
benefit from products that improve starch,
protein and fibre digestibility. However,
before beneficial enzymes can be included
in the diet, a reliable method of applying
feed enzymes to ruminant feed is required
that accounts for the fermentation
processes of the rumen.
Method of applying feed enzymesResearch to date has shown that the method
of applying the enzymes can significantly
alter their efficacy. The direct infusion of
enzymes into the rumen is far less effective
(Lewis, 1996) or can even reduce digesti-
bility of forage compared with application
of liquid enzyme to hay. Direct application
is thought to be more effective as a result of
binding of the feed enzyme to its substrate,
rather than the enzyme being broken down
in the rumen fluid by endogenous protease
enzymes.
The effect of feed enzymes on in vivo
digestibility is influenced by the moisture
content of the forage prior to enzyme
application. Feng et al. (1996) applied a
cellulase and xylanase enzyme mixture to
fresh and wilted hay with no effect. When
the enzymes were added to dry forage
immediately before feeding, however, they
improved dry matter and neutral detergent
fibre digestibility.
Given the importance of combining the
enzyme with the feed prior to its entry into
the rumen, it is important to know if there
is an optimal enzyme treatment period.
Treacher and Hunt (1996) reported on
unpublished research which showed
increases in gas production immediately
after enzymes were added to maize silage.
The maximum gas production occurred
after 4 h of combining the enzymes and
maize silage. The authors noted that their
in vitroresults do not necessarily indicate
that enzyme addition was increasing
volatile fatty acid (VFA) production. Yet
the gas production results in combination
with changes in the structure of this silage
(measured by near infrared spectroscopy)
suggest that as little as 2 h between enzyme
application and feeding may be required to
maximize the effect of the enzymes on
maize silage digestibility.
Much more work is required to
elucidate fully the optimum treatment
period for enzyme formulations for typical
dietary ingredients. This lack of knowledge
is important because there are two main
ways of using enzymes in ruminant feeds.
In the first method, the feed is treated with
an enzyme preparation well before it is
offered to the animal. In the second, the
feed enzyme is added to the feed within
1 h of it being offered.416 D.I. Officer