Hello everyone. My name is Vanessa Lagos. I am a second year PhD student under
Dr. Hans Stein, and today I will be talking about the effect of formulating
diets based on a ratio between STTD calcium and STTD phosphorus and the
inclusion of phytase on growth performance, plasma calcium and phosphorus, and
bone ash of pigs from 11 to 130 kilograms.

To start with a short background: currently, calcium requirements are expressed
as total calcium. And how this calcium value is obtained is by multiplying the
requirement for standardized total tract digestible phosphorus by 2.15. However,
it is not clear where this 2.15 value is coming from. And the NRC actually
stated that a ratio between digestible calcium and digestible phosphorus would
be preferred if the data for the digestibility of calcium in feed ingredients
were available.

And now, values for the standardized total tract digestibility of calcium in
mineral supplements, plant feed ingredients, and animal feed ingredients were
generated in diets without the inclusion of phytase or in some cases with the
inclusion of phytase.

So having these values, we were able to formulate diets based on standardized
total tract digestible calcium, or STTD calcium. And experiments were conducted
to determine STTD calcium requirements. So to summarize some of the major
findings from these experiments, first it was concluded that diets should be
formulated based on a ratio between STTD calcium and STTD phosphorus instead of
individual values. Second, it is important to identify the target—whether the
pigs are going to be used for reproduction or for meat production. And this is
because the requirement for STTD calcium to maximize bone synthesis is greater
than to maximize growth performance. And finally, the concentration of dietary
calcium is very important because of the negative effect of excess calcium on
growth performance.

So the final experiments were conducted to determine calcium requirements
expressed as a ratio between STTD calcium and STTD phosphorus using different
body weight ranges and targeting growth performance and bone ash. So if diets
are formulated with STTD phosphorus at the requirement, here are the values that
should be used to maximize growth performance or bone ash. However, these four
studies are independent short-term experiments, and therefore a follow-up study
is needed to verify these numbers, especially because there is a correlation
between body weight and the requirement for STTD calcium to STTD phosphorus. So
in terms of bone ash, the value increases as the animal gets older. But for
growth performance, the value decreases as the animal gets heavier. And in
heavier pigs, the difference between the value to optimize bone ash and growth
performance is greater than when the pigs are younger.

Therefore, the objective of this experiment was to test the hypothesis that the
ratios between STTD calcium and STTD phosphorus from short-term experiments may
be applied to pigs fed diets without or with microbial phytase from 11 to 130
kg.

Now, moving into the materials and methods, we used 160 pigs with an average
initial body weight of 11.2 kg. We used a five-phase program from 11 to 130 kg.
And since no experiment was conducted using pigs from 75 to 100 kg, we averaged
the values above and below. In each phase, we formulated four diets using a 2x2
factorial design with two calcium requirement estimates (total calcium or
digestible calcium, meaning a ratio between STTD calcium and STTD phosphorus)
and two phytase inclusion levels 0 or 500 FTU of Quantum Blue. These diets were
based on corn and soybean meal, and to better understand how the diets with
phytase were formulated, in both the diets based on total calcium and digestible
calcium we assume that phytase releases 0.11% STTD phosphorus. However, for
calcium in the diet based on total calcium, we assume that phytase releases
0.16% total calcium. But for the digestible calcium diets, values for the
digestibility of calcium in feed ingredients from diets with phytase were used
to estimate the concentration of STTD calcium in the diet. The calculated value
for total calcium released by phytase ranged from 0.13 to 0.17%. We measured
growth performance parameters, concentration and percentage of bone ash, and
concentration of calcium and phosphorus in plasma of pigs.

So to better understand the timeline of the study, the experiment lasted 126
days. At the end of phase one, growth performance parameters were measured and
one pig per pen was utilized to collect the femur and a blood sample. At the end
of phases two to five, growth performance parameters were measured, and one
blood sample was taken from the same pig in each phase. At the end of the
experiment, all pigs were euthanized and the right femur was collected from one
pig per pen. For growth performance and bone ash, we evaluated the main effect
of requirement estimate (total calcium or digestible calcium), the phytase
effect, and the interaction between requirement estimate and phytase. However,
for plasma calcium and phosphorus, we also included the effect of phase so we
used repeated measurements.

Now let's move into the results.

And we're going to start with growth performance. So first, I would like to set
up this slide. Blue bars represent diets without phytase, and orange bars
represent diets with phytase. Lighter colors indicate that diets were formulated
based on total calcium, whereas darker colors indicate that diets were
formulated based on digestible calcium. So for average daily gain, there was no
interaction between requirement estimate and phytase and no effect of
requirement estimate or phytase.

There was a similar response for average daily feed intake: no effect of
requirement estimate or phytase and no interaction between main effects.

And because there was no effect of the dietary treatments for average daily gain
and average daily feed intake, there was no effect of requirement estimate,
phytase, or interaction between main effects for gain:feed ratio. And although
here I'm showing the results for the overall experimental period, the same
response was observed at each phase.

The only exception was in phase four, where for average daily gain and gain:feed
ratio, a tendency for pigs fed diets based on digestible calcium to have greater
values than pigs fed diets based on total calcium was observed regardless of the
inclusion of phytase.

Now we're looking at the concentration of bone ash at the end of phase 1. So
bone ash was evaluated in terms of grams per femur—and this value is closely
related with the body weight of the pig—and as a percentage of the bone. And for
both grams per femur and percentage, there was no interaction between
requirement estimate and phytase and no effect of requirement estimate or
phytase. This result was expected because as I showed earlier in this
presentation, the difference for the requirement to optimize bone ash and growth
performance is smaller when pigs are younger. And here I want you to keep in
mind the value for the percentage of bone ash in these pigs, which is around
50%, for further discussion.

For the concentration of bone ash at the end of the experiment, day 126, we also
measured the concentration in grams per femur and percentage. And for both,
there was an interaction between requirement estimate and phytase. So when we
look at the concentration in grams per femur, we observe that these values are
greater just because these pigs were heavier, but also we observe that in the
diets without phytase there is a reduction in the concentration of bone ash in
pigs fed diets based on digestible calcium compared with pigs fed diets based on
total calcium. And this is because the digestible calcium diets were formulated
using values that optimize growth performance, and therefore less calcium was
included in these diets. However, in diets with phytase, no differences were
observed in the concentration of bone ash between the two requirement estimates.
For percentage of bone ash, the same pattern was observed. But here, if we look
at the value in heavier pigs, this number is 10 percentage units greater than at
the end of phase one. So this indicates that these pigs have greater bone
mineralization than younger pigs.

For the concentration of calcium and phosphorus in plasma, there was no effect
of requirement estimate or phytase, and there was no interaction between main
effects. However, here we can observe that the value for the concentration of
calcium in plasma is quite constant across diets, and this is because of
hormonal regulation of calcium. Calcium needs to be maintained in plasma in a
level between 8 and 12 mg/dl; however, this is not the case for phosphorus, and
that's why here we observe some variation across dietary treatments.

Now for the concentration of calcium and phosphorus at the end of phases 2 to 5.
Again we used the same pig, so here we are also evaluating the effect of phase.
So here we are looking at the result of concentration of calcium in plasma in
each of the 4 dietary treatments; however, if we look at the statistics, the
only effect that was significant was phase. So if we average the values for the
diets in each phase, we observe that there is a linear and quadratic effect of
phase on plasma calcium. So this indicates that because heavier pigs have
greater bone mineralization than younger pigs, more calcium is needed to
synthesize bone and therefore less is present in the bloodstream.

For the concentration of phosphorus in plasma, we observe a tendency for a
three-way interaction between requirement estimate, phytase, and phase. So if we
look at each one of the diets, there was a quadratic effect in the diet without
phytase and based on total calcium, a linear effect in the diet without phytase
but based on digestible calcium, and a quadratic effect in the two diets with
phytase included. So here again, we observed more variability across diets, but
the quadratic effect of phase again indicates that heavier pigs have greater
bone mineralization and therefore calcium and phosphorus is pulled out from the
bloodstream.

In conclusion, ratios between STTD calcium and STTD phosphorus can be used in
diets for growing-finishing pigs without affecting growth performance. There are
no differences in bone ash between digestible and total calcium diets when
phytase is included. And there is a lower concentration of calcium and
phosphorus in plasma as pigs grow, likely because of a greater bone
mineralization.

With this, I would like to acknowledge AB Vista for the financial support,

and all the members of the Stein Monogastric Nutrition Laboratory. And if you
want to learn more about these or other topics, please visit our website at
nutrition.ansci.illinois.edu. Thanks for listening.