Hello everyone, I’m Jerubella Abelilla and I am a PhD student under Dr. Stein,
and today I will be presenting one of the experiments that we have conducted for
my dissertation. And this presentation was also presented in the previous
Midwest Conference. So this presentation is entitled "Degradation of dietary
fiber in the stomach, small intestine and large intestine of growing pigs fed
corn- or wheat- based diets without or with microbial xylanase.”

I would like to start with three take-home messages. First, fiber hydrolysis
already starts in the stomach of pigs. Second, fermentability of fiber in corn
is different than in wheat. And third, this means that different enzymes may be
needed to degrade the fiber that is present in corn versus that in wheat.

So responses to microbial xylanases has been greater in wheat based diets than
in corn based diets and the exact reason for this has not been fully elucidated.

However, the degradation varies with structure and physicochemical
characteristics of the non-starch polysaccharides. For example, the arabinoxylan
that is present in wheat may have a different structure than the arabinoxylans
that is present in corn and also, the structure of arabinoxylans vary even
within the ingredient itself. And so, it's possible that the arabinoxylan in
corn may be more rigid compared to the arabinoxylans in wheat based diets.

So, there are different dietary fiber components that are present in our feed
ingredients. And this includes soluble hemicellulose, insoluble hemicellulose,
cellulose, and lignin. Hemicelluloses are also what we call non-starch
polysaccharide, and to quantify these fractions, we have what we call acid
detergent fiber, this quantifies cellulose and lignin. We have NDF or neutral
detergent fiber, this includes insoluble hemicellulose, cellulose, and lignin.
And then we also have the soluble dietary fiber which is equivalent to the
soluble hemicellulose, and the insoluble dietary fiber which is basically the
same as the neutral detergent fiber. So the sum of soluble dietary fiber and
insoluble dietary fiber is what we call TDF or total dietary fiber. And we can
also analyze the lignin fraction of our ingredients. And based on this analysis
we will be able to calculate the other dietary fractions. We will be able to
calculate non-starch polysaccharide by subtracting lignin from total dietary
fiber, insoluble hemicellulose by subtracting acid detergent fiber from neutral
detergent fiber, and cellulose by subtracting lignin from acid detergent fiber.

Because of the differences in the concentration of these dietary fiber
fractions, the site of digestion of those dietary fiber fractions are also
affected. Most of the soluble dietary fiber are fermented prior to the colon and
most of the insoluble dietary fiber are fermented in the colon. So clearly,
differences in the digestibility of fiber exists among ingredients.

And also, in a previous experiment they also observed that the digestibility of
fiber in soybean hulls and DDGS was less compared to the digestibility of fiber
in wheat middlings. And again, this indicates that we observe differences in the
digestibility of dietary fiber fractions among ingredients.

However, there had been no study conducted determining the digestibility of
fiber in corn versus the fiber in wheat-based diets. And so, the objective of
this experiment was to test the hypothesis that microbial xylanases may
contribute to the degradation of fiber in wheat- and corn- based diets along the
intestinal tract of pigs.

Moving on to the materials and methods, we formulated two diets based on two
different sources of dietary fiber. We have corn-based diets, which is composed
of 71.4% corn and 24% soybean meal; and wheat-based diets, which is composed of
73.75% wheat and 22 percent soybean meal. To increase the concentration of
dietary fiber, we included 30% of DDGS to the corn-based diets and 30% wheat
middlings to the wheat-based diets at the expense of corn and soybean meal. And
all of these four diets were formulated to contain no xylanase and another set
of these four diets were formulated to contain xylanase A and another set of
these four diets to contain xylanase B for a total of 12 different diets.

These twelve diets were randomly allotted to a 24 x 4 Youden square with 24
double cannulated pigs, with one cannula at the proximal end of the duodenum and
one cannula at the end of the ileum, and four periods for a total of eight
replicate pigs per diet. So each period consisted of eighteen days with the
initial seven days of adaptation period to the diet, fecal and urine collection
on day 8 to 13, and ileal digesta collection on day 15 to 16 and duodenal
digesta collection on day 17 to 18.

We calculated the apparent duodenal digestibility; this reflects the
digestibility of fiber in the stomach of the pigs. We also calculated the
apparent ileal digestibility, and this reflects the hydrolysis of fiber at the
end of the small intestine of the pigs, and the apparent total tract
digestibility, which reflects the digestibility of fiber along the
gastrointestinal tract of the pigs. So we calculated all of these digestibility
values among the different fractions of dietary fiber. But, for this
presentation, I will only show you the digestibility of insoluble hemicellulose,
mainly because more than 50% of the insoluble hemicellulose is composed of
arabinoxylans and arabinoxylans is our main substrate for the microbial xylanase
supplementation. I will also show you the digestibility of gross energy as well
as the metabolizable energy of the diets.

Moving on with the results: to set up the slides, the vertical axis represents
the percent digestibility and the horizontal axis represents the digestibility
of each of the diets. Yellow bars represent diets containing no xylanases, blue
bars represent diets containing xylanase A, and orange bars represent diet
containing xylanase B. So we can observe here that there is a very low
digestibility of insoluble hemicellulose by the end of the stomach, and this is
expected because there is not a lot of microbial growth in the stomach of the
pigs. And we also observe that supplementation of microbial xylanase improved
the duodenal digestibility of insoluble hemicellulose in the wheat-based diets
but that was not the case in the corn-based diets. And this indicates that the
structure of insoluble hemicellulose in wheat is less rigid compared to the
insoluble hemicelluloses in corn. And also, we observed that addition of DDGS to
the corn-based diets improved the duodenal digestibility of insoluble
hemicellulose which may be associated to the fermentation process of producing
DDGS from corn. However, we did not observe an improvement if wheat middlings
was added to the wheat based diets, indicating that feed milling did not improve
the digestibility of insoluble hemicellulose. And also we can observe here that
there's greater digestibility of insoluble hemicellulose in wheat-based diets
compared to the corn-based diets, and again indicating that the structure of
insoluble hemicelluloses in wheat-based diets is less rigid compared to the
insoluble hemicellulose in corn-based diets. For the duodenal digestibility of
gross energy, which is not in this presentation, we observed less than 5% or 0%
digestibility of gross energy in the stomach, and this is expected because we
don't have absorption of monosaccharides in the stomach of the pigs. This also
indicates that although we observed an improvement in the digestibility of
insoluble hemicellulose, we did not observe an improvement in the digestibility
of gross energy.

Moving on to the ileal digestibility of insoluble hemicellulose, again, we
observed an improvement on the ileal digestibility of insoluble hemicellulose if
DDGS was added to the corn-based diets. And again, this may be associated to the
fermentation process to produce the DDGS and thereby it's possible that through
that process some of the insoluble fractions of the fiber are solubilized.
However, again, we did not observe an improvement if wheat middlings was added
to the wheat-based diets indicating that the feed milling did not improve the
ileal digestibility of insoluble hemicellulose. And also, generally, we observed
that the ileal digestibility of insoluble hemicellulose in wheat-based diets is
greater than the ileal digestibility of insoluble hemicellulose in corn, and
again indicating that the structure of insoluble hemicellulose in wheat is less
rigid compared to that in corn. And also, we did not observe any improvement
with microbial xylanase supplementation regardless of the grain source or the
fiber concentration.

For the ileal digestibility of gross energy, we observed a greater ileal
digestibility of gross energy in corn versus that in the wheat-based diets, and
this is expected because of the greater concentration of starch in corn compared
to that in wheat. And also, we observed a reduction in ileal digestibility of
gross energy if DDGS was added to the corn-based diets or if wheat middlings was
added to the wheat-based diets, because of increasing the concentration of the
insoluble portions with the inclusion of these coproducts.

For the total tract digestibility of insoluble hemicellulose, again, as we have
observed for the duodenal digestibility, we observed an improvement if microbial
xylanase was added to the wheat-based diets, but that was not the case in corn.
And also we observed greater total tract digestibility of insoluble
hemicellulose in the wheat-based diets than in the corn-based diets, and again,
this may be associated to a less rigid structure of the insoluble hemicellulose
in wheat versus that in corn.

For the total tract digestibility of gross energy, again we observed greater
digestibility of gross energy in corn-based diets compared to the wheat-based
diets and again, this is expected because of the greater proportion of
digestible energy in corn versus that in the wheat-based diets. And again, we
observed a reduction in the total tract digestibility of gross energy if DDGS
was added to the corn-based diets or if wheat middlings was added to the
wheat-based diets, because by including these coproducts, we are increasing the
concentration of dietary fiber and reducing the amount of starch in the diets

For the metabolizable energy, we observed a greater reduction in the
concentration of metabolizable energy if wheat middlings was added to the
wheat-based diets then if DDGS was added to the corn-based diets. And this may
be associated to the fact that when there is a release of pentoses in the small
intestine of the pigs and they get absorbed, some of those pentoses are excreted
into the urine and analyzed as energy, thereby reducing the metabolizable energy
of the diet. We did not observe an overall effect of microbial xylanase
supplementation mainly because we did not observe an improvement in the
corn-based diets. However, if we will only focus on the wheat-based diets, we
observed an improvement on the metabolizable energy if microbial xylanases were
added.

So to sum it up, the duodenal, ileal, and apparent total tract digestibility of
insoluble hemicellulose in wheat-based diets is greater compared to the
corn-based diets. And also, the digestibility of gross energy and concentration
of metabolizable energy in corn-based diets was greater than in the wheat-based
diets. We observed an improvement in the duodenal and total tract digestibility
of insoluble hemicellulose and metabolizable energy when xylanases were
supplemented to the wheat-based diets, but that was not the case in the corn.
And also, we observed an improvement in the duodenal and ileal digestibility of
insoluble hemicelluloses if DDGS was added to the corn-based diets, but we did
not observe any differences if wheat middlings was added to the wheat-based
diets. But the overall, or the total tract digestibility, we did not observe any
differences if DDGS was added to the corn-based diets or if wheat middlings was
added to the wheat-based diets, indicating that the fermentation process to
produce DDGS or the feed milling did not affect the digestibility of insoluble
hemicellulose in these feed ingredients. Also, we observed that there was a
reduction in the digestibility of gross energy and concentration of
metabolizable energy if DDGS or wheat middlings was added to the corn- or
wheat-based diets respectively.

In conclusion, hydrolysis of fiber prior to the ileum is greater in wheat than
in the corn-based diets, and there was no apparent effect of xylanase and
dietary fiber degradation and metabolizable energy in corn-based diets. However,
we observed an improvement if microbial xylanase is added to the wheat-based
diets.

And with that, I would like to acknowledge DuPont for funding this experiment
and also the Stein Monogastric Lab for all the support and help for this
experiment. And thank you, everyone, for listening and if you want to know more
you can visit our website.