The site of absorption of calcium from the intestinal tract of growing pigs

The site of absorption of calcium from the intestinal tract of growing pigs


Hi, this is Caroline González-Vega from the
University of Illinois. And this is a study that we conducted about the site of absorption
of calcium from the intestinal tract of growing pigs. This is the outline of the presentation. First,
I would like to start with a short introduction about the place that calcium is absorbed,
and also some factors that influence calcium digestibility. Then, I will mention the objectives
of this study, the materials and methods that we used, the results and the discussion, and
finally some conclusions. It has been reported that most of the calcium
is absorbed in the small intestine of the pigs. However, there is not clear data about
if calcium is absorbed either in the stomach or in the large intestine as well. It’s important
to know where calcium is absorbed in order to know what type of collection we should
use for calcium digestibility studies. So, we can know if we can use duodenal, ileal
or total tract collections. Also, there is not available data bout the amount of endogenous
calcium that is lost in the different parts of the gastrointestinal tract. These are some factors that we should consider
for calcium digestibility studies, because these are factors that can influence calcium
digestibility. For calcium level, it has been reported that increasing the level of calcium
in the diet using calcium carbonate as source of calcium does not affect the apparent digestibility
of calcium, but reduced the digestibility of phosphorus. However, there is not data
about what effect has the level of calcium in calcium and phosphorus digestibility when
an organic source is used. Another fact that we should consider is phytate. Phytate is
a molecule that can bind calcium; therefore, it reduces the digestibility of calcium. And
we want to know if phytate has the same effect on organic sources of calcium and inorganic
sources of calcium. Therefore, the objectives of this experiment
are to determine digestibility of calcium in calcium carbonate as inorganic calcium
source, and Vistacal as organic calcium source. And we want to know the effect that has the
level of calcium and the level of phytate in the digestibility of calcium in these two
sources. Also, the other objective is to determine the site in the gastrointestinal tract where
calcium is absorbed. So for this experiment, we used two sources
of calcium. Calcium carbonate, which was mined in Iowa, and contains almost 39% of calcium.
And the other source was Vistacal, which was produced from Lithothamnium calcareum algae
in Ireland, and contains almost 33% of calcium. We formulated nine diets. One diet was a calcium-free
diet, and the other eight diets were formulated using one of the two sources of calcium: calcium
carbonate or Vistacal. And we had two levels of calcium: 0.4 and 0.8. The reason that we
used these two levels of calcium is because we wanted to be lower and higher than the
requirement, which is 0.6% of calcium. And we used two level of phytate: 0 and 1%. This is the composition of the calcium-free
diet. Here, the sources of protein are corn gluten meal and potato protein. The reason
that we used these two sources of protein is because these protein sources are relatively
low in calcium concentration. So, we can add protein without adding calcium into the diet.
Also, we used Solka floc as a source of fiber and monosodium phosphate as a source of phosphorus,
because monosodium phosphate does not contain calcium. We used chromic oxide as an indigestible
marker. So for the other diets, for the calcium carbonate diet we included either one or two
percent to get 0.4 or 0.8% of calcium in the diet. And we added this amount of calcium
carbonate at the expense of cornstarch. We did the same with Vistacal, with 1.25 or 2.52%.
And for phytate, we added 2% of phytate to get 1% of phytate in the diets, because we
used a 50% solution, and this is a synthetic and pure form of phytate. We used nine growing pigs with initial body
weight 23.8 kg, and the pigs were surgically equipped with two T-cannulas, one in the duodenum
and the other in the ileum. The duodenal cannula was placed ten cm after the pancreatic duct,
and the ileal cannula was placed at the end of the ileum. And also, we collected fecal
samples. So, collecting duodenal, ileal, and fecal samples, we were able to calculate duodenal,
ileal, and total tract digestibilities. The pigs were fed twice per day. And they
had an adaptation period for the first four days , and the fecal samples were collected
on days 5 and 6, the ileal samples were collected in days 7 and 8, and duodenal samples were
collected in days 9 and 10. This is the experimental design. It was a
2x2x2x3 factorial with two calcium sources, two calcium levels, two phytate levels, and
three collection sites. We analyzed the data using MIXED procedure of SAS, and because
the phytate level was not significant, then we removed it from the model, and we analyzed
the data as a 2x2x3 factorial, with fixed effects calcium source, calcium level, collection
site, and all possible interactions. And the random effect was period. Now, let’s move to the results. These are the endogenous losses of calcium.
For the duodenal endogenous losses of calcium, we determined that was 1.03 g/kg dry matter
intake. This is likely due to the endogenous calcium secretion from saliva, gastric juice,
bile, and pancreatic juice. In the ileal endogenous losses of calcium, we determined 0.42 g/kg
dry matter intake. And it was less than the duodenal endogenous loss. Therefore, we suggest
that some of the calcium that is endogenously secreted is reabsorbed in the small intestine.
And for the fecal endogenous losses of calcium, we determined 0.67 g/kg dry matter intake.
And this was greater than the ileal endogenous losses of calcium, but less than the duodenal
endogenous losses of calcium. This is the standardized digestibility of
calcium, and we got a significant interaction between calcium source and calcium level.
But first, let me set up the slide. In the y-axis, we have the average of the standardized
duodenal, ileal, and total tract digestibility of calcium. And in the x-axis, we have the
level of calcium, 0.4 and 0.8%. And the orange line represents calcium carbonate, and the
blue line represents Vistacal. So as you can see here, at 0.4% of calcium in the diet,
the digestibility of calcium was greater in calcium carbonate than in Vistacal. And it
was the same when we increased the level of calcium to 0.8%, where calcium carbonate is
still greater than Vistacal. As you can see, when calcium carbonate was used, increasing
the level of calcium did not affect the digestibility of calcium. However, when Vistacal was used,
increasing the amount of calcium in the diet negatively affected the digestibility of calcium. This was another significant interaction,
between calcium source and site of absorption. For duodenal digestibility, the digestibility
of calcium was greater when calcium carbonate was used compared to Vistacal. And it was
the same for ileal and total tract digestibility of calcium. So as you can see, for calcium
carbonate, there was not a difference among collection sites. This suggests that most
of the calcium from calcium carbonate was absorbed before the duodenal cannula. This
suggests that calcium could be absorbed in the stomach or upper duodenum, or both. For
Vistacal, the ileal digestibility of calcium was greater than the duodenal digestibility
of calcium, suggesting that there was an absorption in the small intestine. However, between ileal
and total tract digestibility of calcium, there was not a difference, suggesting that
there was not an absorption of calcium in the large intestine. And this was the same
case for calcium carbonate. So, because there is not a difference between ileal and total
tract digestibility of calcium, this suggests that we can use either ileal or total tract
collections for calcium digestibility studies. But for practical reasons, we recommend to
use total tract collections. So in conclusion, duodenal endogenous losses
of calcium are greater than ileal and total tract endogenous losses of calcium. Phytate
did not have an effect on calcium digestibility, and this is likely because we used a synthetic
form of phytate, so we believe that maybe there are some differences in the properties
between a synthetic phytate and a phytate that is naturally present in the plants. The
effect of calcium level depends on the calcium source, so if calcium carbonate was used,
the calcium level did not affect the calcium digestibility, but if Vistacal was used, then
the calcium level decreased the calcium digestibility. And also, the site of absorption depends on
the calcium source. So when calcium carbonate was used, most of the calcium was absorbed
in the stomach and upper duodenum, and for Vistacal, some calcium was able to be absorbed
in the jejunum or ileum. With this, I want to thank you for your attention.
For more information about this and other topics about monogastric nutrition, you can
visit our website: nutrition.ansci.illinois.edu. Thank you once again.

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