Hi. I'm Diego Navarro from the Stein Monogastric Nutrition Laboratory at the University of
Illinois, and today I will be talking about the effects of inclusion rate of high-fiber
dietary ingredients on the calculated concentration of digestible and metabolizable energy
in mixed diets fed to growing pigs.

In recent years, there has been an increase in the usage of high-fiber co-products in
diets fed to pigs. However, if these co-products are included at high concentrations in
the diet, this may result in a reduction in growth performance due to the dilution of
energy content of the diet as well as a decreased digestibility of nutrients. Pigs do not
secrete enzymes that can digest dietary fiber, but microbial populations in the intestinal
tract may ferment fiber and synthesize short chain fatty acids that may be absorbed and
contribute to the energy status of the pig.

Another possible reason for the reduction in growth performance is that dietary fiber may
also decrease the transit time of digesta through the gastrointestinal tract of the pig.
However, this is not always observed in animal trials, as was the case in a study by
Urriola and Stein where DDGS had no effect on the time of first appearance of digesta in
the ileum, cecum, and in the feces.

So now I will transition to how energy digestibility in feed ingredients is determined.
Using the direct procedure, energy is supplied by the test ingredient alone. If it is not
possible for the test ingredient alone to supply energy, then the diet is formulated with
other feed ingredients that are also a source of energy and therefore digestibility is
calculated by difference. Total collection or the index method may be used for either
procedure. The total collection method requires a quantitative record of feed intake and a
quantitative collection of fecal and urine output along with the use of colored markers to
indicate the start and the end of collection. The index method avoids the need for
quantitative records of feed intake and collection of urine and feces and uses an
indigestible marker to determine digestibility.

A limitation with the difference procedure is that inclusion rate may have an effect on
the calculated energy values in test ingredients. Huang and others observed that
calculated concentration of digestible and metabolizable energy in soybean meal were not
affected by its inclusion rate in the test diet, however an increase in the calculated DE
and ME was observed with increasing concentrations of wheat middlings in the diet. On the
other hand, Zhao and others observed a decrease in the apparent total tract digestibility
of gross energy and the concentration of digestible energy in wheat bran as its inclusion
rate increased in the diet. These contradicting results in the literature present a need
to further investigate the effects of inclusion rate on energy determination.

Therefore, the objectives of this experiment was to determine the effects of inclusion
rate of high fiber dietary ingredients on 1) the calculated values for digestible and
metabolizable energy, and 2) the first appearance of digesta at the end of the ileum and
in the feces. The four high-fiber ingredients used included canola meal, corn germ meal,
sugar beet pulp, and wheat middlings, which are all common feed ingredients included in
swine diets.

Twenty ileal-cannulated barrows with initial body weight of around 31 kg were housed in
metabolic crates and allotted into a replicated 10 x 4 incomplete Latin square design with
ten diets and four 26-day periods. So this gives us two pigs per diet per period with a
total of eight replicate pigs per diet.

Each 26-day period consisted of 14 days of adaptation to the experimental diets. This was
followed by five days of urine and fecal collection, and then a two-day ileal collection
on days 22 and 23. On day 24, an indigestible colored marker was mixed with the morning
meal and the time of ingestion was considered time zero. Time of first appearance in the
ileum and in the feces was recorded once the marker was observed in the cannula and in the
feces, respectively.

The experimental diets included a corn and soybean meal basal diet and a corn-soybean
meal-30% corn starch diet. Six additional diets were formulated by replacing 15 or 30%
corn starch with 15 or 30% corn germ meal, sugar beet pulp, or wheat middlings. An
additional two diets were formulated by including 15 or 30% canola meal in a diet
containing corn-soybean meal-30% corn starch at the expense of corn and soybean meal. Corn
starch was used so that added fiber was supplied by the test ingredient alone.

The concentration of digestible energy in the corn-soybean meal diet was determined and
the contribution of corn and soybean meal to the digestible energy in all other diets was
calculated. And by difference,the digestible energy in corn starch was calculated and the
contribution of corn starch to the digest in test diets containing corn starch was
determined. By calculating the contribution of both the corn starch and the corn and
soybean meal to the test diets, the digestible energy in test ingredients was calculated
by difference. And the same goes with the calculations for metabolizable energy.

The effects of adding 15 or 30% of each high-fiber ingredient to the corn-soybean
meal-corn starch basal diets were analyzed using orthogonal contrasts. Independent-sample
t-tests were conducted using the TTEST procedure to compare response variables between 15
and 30% inclusion rate within each ingredient.

Now, moving on to the results: The apparent hindgut disappearance of gross energy in the
diets, which is calculated as the difference between the apparent total tract
digestibility and the apparent ileal digestibility of gross energy, linearly increased as
the inclusion rate of canola meal, corn germ meal, or sugar beet pulp in the diets
increased compared with the corn starch diet, but not with the addition of wheat
middlings. In contrast, the apparent ileal digestibility and the apparent total tract
digestibility of gross energy in the diets linearly decreased as the inclusion rate of
test ingredients increased compared with the corn starch diet. This indicates greater
amounts of fermentation due to increased nutrient flow into the hindgut as a result of a
fiber-induced decrease in dry matter digestibility in the small intestine.

As a result and as we expected, the concentration of metabolizable energy linearly
decreased compared with the corn starch diet as inclusion rate of canola meal, corn germ
meal, sugar beet pulp, or wheat middlings in the diet increased. And the same trend was
observed with the concentration of digestible energy. The reduction in concentration of
digestible and metabolizable energy  in the diet is due to the replacement of starch with
fiber fractions that are less digestible and make less contribution to DE and ME.

On the other hand, inclusion rate did not significantly affect the apparent total tract
digestibility of gross energy in any of the ingredients. And the same trend was observed
for the apparent ileal digestibility and apparent hindgut disappearance of gross energy in
the ingredients.

Similarly, the concentration of digestible energy in the ingredient on a kcal/kg dry
matter basis was not significantly affected by inclusion rate. 

And the same trend was observed in the concentration of metabolizable energy in
ingredients. This means that the calculated metabolizable energy value measured at 15%
inclusion was also accurate when measured at 30% inclusion rate of test ingredients.

In this experiment, the time from feed ingestion to first appearance of digesta at the end
of the ileum was not significantly affected by addition of test ingredients compared with
the corn starch diet.

In contrast, the time from feed ingestion to first appearance in the feces was linearly
reduced as the inclusion rate of canola meal, corn germ meal, sugar beet pulp, or wheat
middlings in the diet increased. This may explain the reduction in apparent total tract
digestibility of gross energy in diets that was observed as the inclusion rate of
high-fiber ingredients increased, resulting in a decrease in transit time in the hindgut
and therefore less time for digesta to be fermented.

In conclusion, inclusion rate did not affect the calculated values for the concentration
of digestible or metabolizable energy in feed ingredients with relatively high
concentrations of fiber. However, as expected, the concentration of digestible and
metabolizable energy in diets linearly decreased as the inclusion rate of these high-fiber
ingredients increased. This may be a result of reduced transit time of digesta in the
hindgut of pigs fed high-fiber diets, indicated by the reduction in the time of first
appearance of the marker in the feces. But this had no impact on calculated values for
digestible and metabolizable energy in test ingredients.

As a take-home message, microbial capacity for fermentation of fiber is not overwhelmed by
30% inclusion of high-fiber ingredients. Fiber-induced reduction in transit time is more
evident in the hindgut of growing pigs.

I would like to acknowledge Agrifirm Innovation Center of the Royal Dutch Agrifirm for
financial support of this project.

And if you would like to know more about fiber nutrition, I would encourage you to visit
our website at nutrition.ansci.illinois.edu. Thank you.