Hi, my name is Caroline Gonzalez-Vega, and I'm a PhD student in Dr. Stein's lab.
And today, I have the pleasure to talk about the effect of fiber and fat on
calculated values for standardized total tract digestibility of calcium in fish
meal.

This is the outline of the presentation. First, I will start with a short
introduction, and then I will explain the two experiments that we conducted,
followed by the conclusions and implications.

All commercial diets contain plant ingredients. And plant ingredients contain
phytate. Therefore, when we supplement diets with calcium, some of this calcium
is bound to phytate, reducing the availability of calcium to be absorbed.

But if we add phytase in the diet, the digestibility of calcium increases,
because phytase hydrolyzes the molecule of phytate, releasing phosphorus and
also reducing the chance of phytate to bind calcium. Therefore, the
digestibility of calcium and phosphorus increases if phytase is used.

On the other hand, semisynthetic diets are used in digestibility studies. But
these diets do not contain phytate if cornstarch and casein are used. Therefore,
calcium-phytate complexes are not formed.

So if we add phytase in this diet, phytase may not affect the digestibility of
calcium. And so far, we know that calcium from inorganic sources may be bound to
phytate, but to our knowledge there is no data about the effect of phytate and
phytase on animal calcium sources fed to pigs.

Due to the relatively low calcium concentration in plant sources, calcium needs
to be supplemented in the diets. We can supplement this calcium by using
inorganic calcium sources or animal calcium sources. However, to our knowledge,
the effect of phytate and phytase on animal calcium sources has not been
reported.

Therefore, we decided to conduct an experiment to evaluate the effect of phytate
and phytase on the standardized total tract digestibility of calcium in fish
meal.

The objective of this experiment was to test the hypothesis that inclusion of
microbial phytase increases the standardized total tract digestibility of
calcium in fish meal in diets containing phytate.

We used for this experiment 40 growing pigs with initial body weight of 19.2 kg.
And we allotted them into our randomized complete block design with five
treatments. Fecal samples were collected using the marker to marker approach.

In this experiment, we used fish meal that contained 5.7% calcium. And we
included casein as the protein source because it only contains 0.03% calcium and
does not contain phytate. We used corn and corn germ as our phytate sources, and
corn only contains 0.01% calcium, and corn germ contains 0.08% calcium.

These are the diets that we used for this experiment. We had two fish
meal-cornstarch diets, one without phytase and the other with 500 phytase units.
These diets contained fish meal, casein, and cornstarch. The other two diets
contained fish meal, corn, and corn germ, without and with phytase. For these
diets, we included fish meal, casein, corn, and corn germ. A calcium-free diet
was formulated to estimate the endogenous losses of calcium.

We calculated the STTD of calcium and the ATTD of phosphorus. And we analyzed
the data using Proc Mixed of SAS as a 2x2 factorial with 2 levels of phytate and
2 levels of phytase, and we used Orthogonal CONTRAST statements to compare diets
as well.

Now, let's move into the results.

First, let's take a moment to set up the slide. The orange bars represent the
diet with no phytase, and the blue bars represent the diets with phytase. On the
x axis, we have the standardized total tract digestibility of calcium, and the
apparent total tract digestibility of phosphorus. And underneath, we have the P
value for the effect of phytase. The y axis is expressed in percentage. So here,
we have the fish meal-cornstarch diets, and we can see that inclusion of phytase
did not effect the STTD of calcium and the ATTD of phosphorus. And this is in
agreement with what we expected, because there was no phytate in the diet.

Now, looking at the fish meal-corn-corn germ diet, we can see that if we add
phytase in the diet, the digestibility of calcium and digestibility of
phosphorus increased. This is also in agreement with what we expected, because
phytase hydrolyzed phytate that was present in corn and corn germ. Therefore, it
reduced the chance of forming calcium-phytate complexes.

In this slide, we show the standardized total tract digestibility of calcium in
the four diets again. Because as you can see, when we compare the two groups of
diets, the diets that contained fish meal, corn, corn germ have greater
standardized total tract digestibility of calcium than the fish meal-cornstarch
diets.

We know that corn and corn germ have phytate, but it is not possible that
phytate is the responsible factor for this increase. Therefore, there may be
other factors such as fiber or fat that may influence the standardized total
tract digestibility of calcium in these diets.

Therefore, we decided to conduct another experiment to determine the effect of
fiber and fat on the standardized total tract digestibility of calcium.

We know that fiber increases the rate of passage. Therefore, the nutrients have
less time to be digested by the enzymes and be absorbed in the gastrointestinal
tract. But also, fiber can change the pH in the intestines. Therefore, it
enhances the solubility of some minerals, resulting in an increased
digestibility.

We know that fat decreases the rate of passage. Therefore, the nutrients have
more time to be digested by the enzymes and be absorbed in the gastrointestinal
tract. But also, we know that fat may form some calcium-fat complexes, reducing
the availability of calcium to be absorbed.

The objective of this experiment was to test the hypothesis that fiber or fat
may influence the STTD of calcium.

These are the diets that we used for this experiment. We have a fish
meal-cornstarch diet. This diet contained fish meal, casein, and cornstarch. It
was similar to the fish meal-cornstarch diet that we used in the first
experiment. The fish meal with fiber diet was similar to the previous diet, with
the exception that Solka Floc, a source of cellulose, was included at the
expense of cornstarch. The fish meal with corn diet contained the same amount of
fish meal and casein, but cornstarch was replaced by corn. The fish meal, corn,
and fat diet was similar to the previous diet, with the exception that soybean
oil was included at the expense of corn. A calcium-free diet was formulated to
estimate the endogenous losses of calcium.

For this experiment, we used 50 growing pigs with initial body weight of 19.4
kg, housed individually in metabolism cages. the STTD of calcium and the ATTD of
phosphorus were calculated, and the data were analyzed using the Proc Mixed of
SAS, and Orthogonal CONTRAST statements were used to compare the diets.

So, let's move into the results.

Here, the blue bars represent the fish meal-cornstarch, and the yellow bars
represent the fish meal-corn diet. Here, we compared the cornstarch diet and the
corn diet. And as you can see, the standardized total tract digestibility of
calcium and the apparent total tract digestibility of phosphorus is reduced if a
cornstarch diet is used compared with a corn diet. One possible explanation for
this observation is that soluble fiber from corn gets fermented, and the
production of short chain fatty acids lowers the pH, enhancing the solubility of
the minerals, which increases the digestibility of calcium and phosphorus.

Here, the blue bars represent the fish meal-cornstarch diet, and the green bars
represent the fish meal-cornstarch with fiber diet. Here, we observe that the
fish meal-cornstarch diet reduced the STTD of calcium and the ATTD of phosphorus
compared with the fish meal-cornstarch with fiber diet. Remember that the source
of fiber here is pure cellulose, which is not fermentable. Therefore, here,
there is no production of short chain fatty acids, which may indicate that maybe
there is another factor that may be responsible for the effect on the STTD of
calcium and the ATTD of phosphorus. Another possible explanation is that in the
fish meal-cornstarch diet, precipitation of minerals occurs. Therefore,
additional fiber may avoid some precipitation,  which results in an increased
digestibility of calcium and phosphorus.

Here, the yellow bars represent the fish meal-corn diet, and the orange bars
represent the fish meal-corn with fat diet. Here, we observe no difference in
the standardized total tract digestibility of calcium and the apparent total
tract digestibility of phosphorus between the fish meal-corn diet and the fish
meal-corn with fat diet. Therefore, fat did not have any effect on the STTD of
calcium and the ATTD of phosphorus.

Here, we show the STTD of calcium in the four diets again. So as you can see,
the fish meal-cornstarch diet had the least STTD of calcium. Fiber increased the
STTD of calcium, but not as much as the fish meal-corn diet, which is almost
double than the fish meal-cornstarch. Therefore, there are some factors such as
production of short chain fatty acids or avoiding precipitation of the minerals
or other factors that we are not aware that are responsible for these
differences.

In conclusion, phytase increased the STTD of calcium and the ATTD of phosphorus
in diets containing phytate. Semisynthetic diets, or cornstarch diets, reduced
the STTD of calcium and the ATTD of phosphorus in fish meal.

Fiber increased the STTD of calcium. This may be by production of short chain
fatty acids, or avoiding precipitation of minerals. Fat did not affect the STTD
of calcium.

Results from these two experiments indicate that values for STTD of calcium from
corn diets may be more representative of commercial diets.

With this, I want to thank you for your attention. And if you want to see more
information about monogastric nutrition, you can visit our website and "Like" us
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