Hi, everyone. My name is Su A Lee from the Stein Monogastric Nutrition Laboratory at the
University of Illinois. I will be discussing determining digestibility of calcium in
different sources of calcium carbonate and dicalcium phosphate.

Here is the outline of the presentation. First of all, I am going to introduce some
background and the objectives. There are two experiments conducted to evaluate calcium
sources. Experiment 1 will be about calcium carbonate and Experiment 2 will be about
dicalcium phosphate. In each section, materials and methods and results will be provided.
Finally, I will draw conclusions.

Let’s start with the introduction of this experiment.

Calcium in diets tends to be oversupplied. One of the most possible reasons is that
calcium sources, such as calcium carbonate, are relatively inexpensive compared with other
feed ingredients, meaning that there will be no harm if we put more of a cheaper feed
ingredient when formulating diets. Another possible reason is that a lot of feed
additives, or sometimes feed ingredients, contain calcium carbonate as a carrier or a flow
enhancer.

What would happen if calcium in diets is too high? The first thing that we should worry
about is phosphorus digestibility. A previous study in 2011 demonstrated that as dietary
calcium increased, shown in the x axis in this graph, digestibility of phosphorus linearly
decreased.

As phosphorus digestibility is decreased by the excessive calcium in diets, the body then
cannot utilize enough phosphorus for bone development, maintenance, or growth. Therefore,
excessive calcium negatively affects growth of pigs, and this has been shown in a number
of previous experiments already.

To prevent oversupply of calcium, therefore, feed ingredients should be evaluated based on
digestible calcium.

When looking at the composition of nutrients in fecal samples of pigs, not only
diet-originated nutrients, but also basal endogenous loss-originated nutrients are
contained. Standardized total tract digestibility is calculated by correcting apparent
total tract digestibility with the basal endogenous loss. And the values for the
standardized total tract digestibility is believed additive in a complete diet.

Phytate from plant feed ingredients including corn, soybean meal, and so on, can bind to
calcium ions in the gastrointestinal tract of pigs because the phytate is a strong
chelator, and, therefore, calcium digestibility decreases. However, use of microbial
phytase may increase not only phosphorus, but also calcium digestibility.

Different suppliers of inorganic sources of calcium may use different raw materials and
different production processes, and the concentration of calcium in calcium-containing
ingredients may vary among suppliers. It is, however, not known if different suppliers of
inorganic calcium influence the standardized total tract digestibility of calcium or the
response to microbial phytase. 

Therefore, two experiments were conducted to test two hypotheses. In Experiment 1, the
hypothesis was that the standardized total tract digestibility of calcium in calcium
carbonate as well as the response to microbial phytase is constant regardless of supplier.
In Experiment 2, the hypothesis was that the standardized total tract digestibility of
calcium in dicalcium phosphate is constant regardless of supplier.

Let’s move on to Experiment 1.

For Experiment 1, we utilized 80 pigs with body weight 19 kg. Four sources of calcium
carbonate were used, and each source was included in a diet containing mostly corn to
provide phytate. A corn-based calcium-free diet was also used to measure the basal
endogenous loss of calcium. In addition to the five diets, five additional diets were also
formulated with microbial phytase to contain 500 units per kg of diet. Therefore, a total
of ten diets were used with eight replicates per diet.

Calcium concentrations in four sources of calcium carbonate ranged from 38.9 to 40.3%.
Calcium in the diets ranged from 0.67 to 0.69%, and phosphorus concentration was fixed to
contain 0.46%.

Eighty growing pigs were housed in metabolism crates. Pigs were fed 2.7 times maintenance
and fed twice a day. After four days of adaptation, total fecal samples were collected for
four days.

The statistical model included calcium carbonate source, phytase, and interaction. For the
calcium-free diet, the model only included phytase as a fixed variable.

Now, we are looking at the basal endogenous loss of calcium from pigs fed the corn-based
calcium-free diet. The basal endogenous loss of calcium was 463 mg/kg of dry matter
intake, and this value was close to the values obtained in the previous data. The basal
endogenous loss of calcium was reduced to 304 mg/kg of dry matter intake when microbial
phytase was supplemented to the calcium-free diet, meaning that phytate from corn can also
bind to calcium ions from the basal endogenous loss of calcium and that use of phytase
releases the calcium from the phytate-calcium complex.

Interaction between phytase and source was not significant. Values for the standardized
total tract digestibility of calcium ranged from 71 to 75% when no phytase was used.
Supplementation of phytase increased the standardized total tract digestibility of calcium
in calcium carbonate. Again, the increase in the digestibility of calcium is because
phytate from the corn chelates calcium from calcium carbonate, and phytase can release the
calcium from the phytate-calcium complex. Regardless of use of phytase, source D had the
least and source A had the greatest values for the standardized total tract digestibility
of calcium.

Let’s move into Experiment 2, where standardized total tract digestibility of calcium in
dicalcium phosphate was determined.

For Experiment 2, we utilized 40 pigs with body weight approximately 15 kg. A basal diet
was formulated to contain corn and calcium carbonate. Three sources of dicalcium phosphate
were used, and each source was included in a diet containing mostly corn to provide
phytate. To adjust the calcium to phosphorus ratio, calcium carbonate was also used in the
three diets. A corn-based calcium-free diet was also used to measure the basal endogenous
loss of calcium. We did not use phytase in Experiment 2 because previous data have shown
that calcium in dicalcium phosphate is not affected by microbial phytase due to calcium in
dicalcium phosphate strongly binding to phosphate instead of phytate. Therefore, a total
of five diets were used with eight replicates per diet.

Calcium concentrations in the three sources of dicalcium phosphate ranged from 18.9 to
20.5%. Calcium in the diets ranged from 0.62 to 0.67%.

Housing, feeding, and sample collection are as described in Experiment 1.

To calculate the apparent and standardized total tract digestibility of calcium in
dicalcium phosphate, the difference procedure was used after calculating a contribution of
calcium from each calcium source in the test diets.

The statistical model included dicalcium phosphate source as a fixed variable.

Values for the standardized total tract digestibility of calcium ranged from 77 to 86%,
and there was no difference among the three sources of dicalcium phosphate.

Digestible calcium in dicalcium phosphate was also calculated, because the concentrations
of calcium and the standardized total tract digestibility of calcium varied among sources.
Results showed that digestible calcium in dicalcium phosphate was not different among the
three sources, and the average was 16.4%.

The three experimental diets contained the same amount of corn, sodium phosphate, and
dicalcium phosphate, and the apparent total tract digestibility of phosphorus in diets was
also calculated. There was no difference in the values among the three diets, and the
average was around 54.8%.

Let’s move into conclusions.

First, values for the standardized total tract digestibility of calcium in calcium
carbonate varied among sources. However, that was not the case for dicalcium phosphate.
Second, the standardized total tract digestibility of calcium in calcium carbonate is
increased by use of microbial phytase. Third, the basal endogenous loss of calcium
decreased if a corn-based calcium-free diet contains microbial phytase because of the
phytate in corn binding to basal endogenous-originated calcium.

These experiments are also published in Journal of Animal Science, so if you would like
see more details of this work, please find the paper. I would like to acknowledge AB Vista
for the financial support, and everyone from Dr. Stein’s lab. And if you want to learn
about the research we are conducting in the Stein Monogastric Nutrition Laboratory, please
visit our website at nutrition.ansci.illinois.edu, or search “Stein” and “pig” on google.
Thank you for listening.