Slide 1

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.

Slide 2

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.

Slide 3

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.

Slide 4

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.

Slide 5

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.

Slide 6

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.

Slide 7 

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%.

Slide 8

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.

Slide 9

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.

Slide 10

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.

Slide 11

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.

Slide 12

Now, let's move to the results.

Slide 13

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.

Slide 14

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.

Slide 15

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.

Slide 16

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.

Slide 17

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.