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Hi. This is Caroline Gonzalez-Vega from the University of Illinois. I'm a Ph. D. student,
and today I have the pleasure to talk about the effects of microbial phytase on the digestibility
of calcium in calcium supplements fed to growing pigs.
This is the outline of the presentation. First, I will start with a short background about
calcium supplements. Then I will mention the materials and methods that we used, and then
we will move into the results and discussion, and finally I will give you some conclusions
and implications.
Most of the diets contain plant ingredients that have relatively low calcium concentration.
Therefore, calcium needs to be supplemented in diets. So there are several calcium supplements
that we can use to add calcium in the diets.
Monocalcium phosphate and dicalcium phosphate, abbreviated as MCP and DCP respectively, are
two products that contain calcium and phosphorus. So MCP contains 16 to 18.5% calcium and 21.5%
phosphorus. DCP contains 21 to 25% calcium and 18.5% phosphorus. These two products are
not in a pure form, but they are a mixture of MCP and DCP. So to understand these, let
me explain how these two products are produced.
We start by adding phosphoric acid into calcium carbonate at 200 degrees Fahrenheit.
And then, MCP and DCP are produced during this process.
So, if in the final product we have 18.5% phosphorus, we call it DCP. And this is a
mixture of MCP and DCP, and as you can see, we have more DCP than MCP.
But if we want more phosphorus in the final product, then we have to add more phosphoric
acid. And if we obtain about 21% phosphorus, we call it MCP. And as you can see, it contains
more MCP than DCP.
Calcium carbonate is one of the calcium sources with the greatest calcium concentration. It
contains 38.5 to 40% calcium and 0.02 to 0.16% phosphorus.
L. calcareum calcium is produced from calcified seaweeds Lithothamnium calcareum, and can
be used as calcium supplements for poultry and pigs. And the product that we used in
this experiment is commercially known as Vistacal, and it contains 34.5% calcium and 0.2% phosphorus.
Sugar beet coproduct is a coproduct is a coproduct of sugar beet production, and it's mostly
used in agriculture for soil conditioning and for correction of soil acidity. The product
that we used in this experiment is commercially known as Limex, and it contains 31.5% calcium
and 0.8% phosphorus.
So now, let me explain the phytate-calcium interactions.
On yellow, we have the plant ingredient that contains phytate and some calcium. Some of
this calcium is bound to phytate. In the white circle, it represents the calcium supplement.
So here, we only have calcium and not phytate.
So when we feed this to the pig, it the gastrointestinal tract, some of the calcium gets bound to phytate.
Therefore, the digestibility of the calcium from the calcium supplement is reduced.
When we add phytase in the diet, then, this phytase is able to break down the phytate,
releasing some of the phosphorus, and also reducing the chance of phytate to bind calcium.
Therefore, inclusion of microbial phytase will result in an increase in the digestibility
of phosphorus and calcium.
So, so far, we know only the calcium concentration in these calcium supplements. There are no
values for standardized total tract digestibility of calcium in pigs. And to our knowledge,
there are no data about the effect of microbial phytase on the STTD of calcium.
Therefore, the objective of this experiment was to test the hypothesis that inclusion
of microbial phytase increases the STTD of calcium.
For this experiment, we used 104 growing barrows with initial body weight of 17.7 kg. We used
13 diets with 8 replicate pigs per diet. And we had fecal collections using the marker-to-marker
approach.
This is the calcium and phosphorus composition of the calcium supplements. And as you can
see, MCP and DCP have substantial amounts of calcium and phosphorus. For calcium carbonate,
L. calcareum calcium, and sugar beet coproduct, they have relatively high calcium concentration,
but relatively low phosphorus concentration.
We used corn and potato protein isolate as an energy and protein source because these
tow ingredients contain relatively low concentration of calcium. Also, because the objective of
this experiment was to test the effect of phytase, then the inclusion of these two ingredients
was ideal to include some phytate in the diet.
These are the diets without phytase. And because we used the difference procedure, we used
a basal diet that contains 88% corn, potato protein isolate, and soybean oil. We also
add 0.8% calcium carbonate and some corn starch, vitamins, and minerals. So, we formulated
the other diets using the basal diet, but we added the calcium supplement at the expense
of corn starch. So, by difference procedure, we will be able to determine the digestibility
of the calcium from the calcium supplement.
This is the chemical composition of the diets. And as you can see, the basal diets contained
0.33% calcium, and the other diets contained from 0.7 to 0.86% calcium. The phytate-bound
phosphorus was similar among diets because all of them contained the same amount of corn
and potato protein isolate. However, the non-phytate phosphorus was greater in the MCP and DCP
diets because these diets contain MCP and DCP that not only add calcium in the diets,
but also phosphorus.
We formulated 6 additional diets similar to the previous diets, with the exception that
we added 500 units of phytase. The microbial phytase that we used is Quantum Blue.
This is the calcium-free diet that we formulated to measure the basal endogenous losses of
calcium and to be able to determine the STTD of calcium.
The STTD of calcium in the diets were determined by using the direct procedure.
And the STTD of calcium in the calcium supplements were determined by using the difference procedure.
The ATTD of phosphorus in the diets were determined by using the direct procedure. And we analyzed
the data for each calcium supplement using the Proc MIXED of SAS, with the fixed effect
of phytase and the random effect of block.
Now, let's move into the results and the discussion.
First, let me set up the slide. In the x-axis, we have the STTD of calcium and the ATTD of
phosphorus. Underneath, we the have P-value for the phytase effect. The orange bar represents
the diets without phytase, and the blue bar represents the diets with phytase. So for
the basal diets, the inclusion of microbial phytase increased the digestibility of calcium
and phosphorus. This may indicate that calcium was bound to phytate, and also that phosphorus
was released from phytate when microbial phytase was used.
For MCP diets, the digestibility of calcium was not affected by the microbial phytase.
So this may indicate that calcium was not bound to phytate, and we believe that this
is because the calcium is already bound to phosphate in this product. Therefore, it's
more difficult for phytate to bind this calcium that is already bound to phosphate. And here
also we observed that the digestibility of phosphorus increased by the inclusion of microbial
phytase. Therefore, some of the phosphorus was released from phytate.
For DCP diets, the digestibility of calcium was not affected by phytase. So we have similar
explanation for this product as the MCP diets. However, the digestibility of phosphorus was
not affected by phytase, and we don't have an explanation for this observation.
These are the calcium carbonate diets. And here we observed that the digestibility of
calcium and digestibility of phosphorus increased with the inclusion of microbial phytase. This
is in agreement with the results obtained from the basal diets that contained calcium
carbonate as the only source of calcium. Therefore, this may indicate that calcium was bound to
phytate.
These are the L. calcareum calcium diets. And here we observed that the inclusion of
microbial phytase did not affect the STTD of calcium. This may indicate that calcium
was not bound to phytate. And we don't know the chemical structure of the calcium present
in this product. But the inclusion of microbial phytase increased the digestibility of phosphorus
due to the release of phosphorus from phytate.
These are the sugar beet product diets. And here we observed that the inclusion of microbial
phytase did not affect the digestibility of calcium. Also, this may indicate that calcium
was not bound to phytate. And we don't know the chemical structure of the calcium in this
product, but here we observed that there is a tendency to increase the digestibility of
phosphorus if microbial phytase was used.
This is the STTD of calcium in the calcium supplements without and with phytase. And
these values were obtained from using the difference procedure. Here we observed that
the inclusion of microbial phytase increased the STTD of calcium in calcium carbonate,
but phytase did not have an effect on the STTD of calcium in MCP, DCP, L. calcareum
calcium and sugar beet coproduct.
In conclusion, the effect of phytase on the STTD of calcium was different in calcium supplements,
and microbial phytase increased the STTD of calcium in calcium carbonate.
Some implications from this research are that we should formulate diets using the STTD of
calcium instead of total calcium values. And also, if nutritionists want to reduce the
diet costs and phosphorus excretion by replacing some MCP or DCP with other calcium sources,
and also including microbial phytase in the diets, they should be aware that the digestibility
of calcium may be different in the calcium supplements, and also that the effect of microbial
phytase is different in calcium supplements.
And with this, I want to thank you for your attention, and also I want to thank AB Vista
for the financial support. And if you want to know more about monogastric nutrition,
please visit our web site. And thanks once again.