Hello. My name is Su A Lee from the Stein Monogastric Nutrition Laboratory at
the University of Illinois. I will be discussing comparative digestibility and
retention of calcium and phosphorus by gestating sows and growing pigs today.

Here is the outline of the presentation. First of all, I am going to introduce
some background and the objectives, and will provide materials and methods,
state the results of digestibility and retention of calcium and phosphorus, and
draw conclusions.

Let’s start with the introduction of this experiment.

Nutrient digestibility has been shown to be affected by physiological state of
pigs. As an example, this graph shows the digestibility of gross energy, neutral
detergent fiber, and crude protein are greater in gestating sows, represented by
orange bars, than in growing pigs, represented in blue bars.

When evaluating calcium and phosphorus availability, standardized total tract
digestibility (STTD) values are preferably used because the STTD values are
believed to be additive in mixed diets. The reason for this additivity is that
basal endogenous loss is considered when the STTD values are calculated.

The values for STTD of phosphorus and calcium in feed ingredients are available
in NRC 2012 and a paper by Stein and his colleagues 2016, respectively.

However, most of the values were obtained from growing pigs and these values
were also used in sows’ practical application.

Therefore, a question remains if the STTD values for calcium and phosphorus are
also applied to diets for sows.

It is well demonstrated that minerals that are positively charged tend to
chelate to phytate when phytate becomes negatively charged. A dietary phytate
then may affect not only digestibility of phosphorus, but also digestibility of
calcium and other cations.

Therefore, the objective of this experiment was to test the hypothesis that no
differences between gestating sows and growing pigs exist for standardized total
tract digestibility and retention of calcium and phosphorus and for the
responses to dietary phytate.

Moving on to the materials and methods, we utilized multiparous sows in
mid-gestation and growing barrows. Initial body weight was about 250 and 20 kg
respectively for the gestating sows and growing pigs.

The gestating sows and growing pigs were fed the same diets, but daily feed
amount was 1.5 and 3 times maintenance requirement for energy respectively for
gestating sows and growing pigs, that are close to what they usually are fed.

After 4-day adaptation, total fecal and urine samples were collected for 4 days
using marker to marker procedure. Therefore, a period consisted more than 8
days.

Two experimental diets were formulated based on corn and soybean meal. To create
the high-phytate diet, 40% full fat rice bran was included. We also utilized
inorganic sources such as dicalcium phosphate and limestone to adjust the level
of calcium and phosphorus in the diets. More dicalcium phosphate was used in the
low-phytate diet than in the high-phytate diet due to the high concentration of
phosphorus in the rice bran.

Analyzed phytate-bound phosphorus to total phosphorus ratio was 46 and 76% for
low- and high-phytate diets, respectively. With similar calcium concentration in
2 diets, the high-phytate diet contained more phosphorus. The calcium to
calculated STTD phosphorus ratio was similar between the 2 diets and these
values were also close to NRC recommendation value.

Two additional diets were formulated to measure the basal endogenous losses of
calcium and phosphorus. A calcium-free diet was formulated based on corn and
potato protein concentrate and a phosphorus-free diet contained cornstarch and
gelatin. 

To calculate STTD values, we first calculated apparent total tract
digestibility, then corrected with the values of basal endogenous losses of
calcium and phosphorus. Using fecal and urine excretions, we also calculated the
retention of calcium and phosphorus.

Data were analyzed using procedure Mixed of SAS. The model included phytate,
physiological state, and the interaction between two factors as the fixed
effects. If an interaction in any response criteria was found, the means were
separated using a p-difference option.

To compare the basal endogenous losses of calcium and phosphorus by gestating
sows and growing pigs, unpaired t-test was used.

Let’s move into the results. 

The basal endogenous loss of calcium that was obtained from growing pigs was
0.43 g/kg dry matter intake. And this value was close to the values that were
reported previously.

Gestating sows had about 3 to 4 times greater basal endogenous loss of calcium
compared with growing pigs. Unlike growing pigs, there were no data reported
previously.

Before we look at the data for STTD of calcium, let me set up the first slide
for the couple of next slides. In the bottom, different physiological
states—that were gestating sows and growing pigs—were presented and were divided
into low or high phytate levels within each physiological state. Lastly, orange
bars represent low-phytate, and blue bars represent high-phytate diets.
Interaction between phytate level and physiological state was observed, that
phytate level did not affect the STTD of calcium by gestating sows, but the STTD
of calcium was greater if growing pigs were fed the low-phytate diet than if
they were fed the high-phytate diet.

Same was observed in the retention of calcium, that phytate level did not affect
calcium retention by gestating sows, but the calcium retention was greater if
growing pigs were fed the low-phytate diet than if they were fed the
high-phytate diet. Regardless of phytate level, gestating sows had reduced
digestibility and retention of calcium compared with growing pigs. And the STTD
and retention of calcium by gestating sows seemed not to be affected by phytate
level.

The basal endogenous loss of phosphorus that was obtained from growing pigs was
0.16 g/kg dry matter intake. This value was close to the values that were
reported previously and a value 0.19 that was summarized by NRC 2012.

Similar with the basal endogenous loss of calcium, gestating sows had about 5
times greater values basal endogenous loss of phosphorus compared with growing
pigs. Unlike growing pigs, there were not many data reported previously.

There was an interaction between phytate level and physiological state, that the
STTD of phosphorus was greater if pigs were fed the low-phytate diet rather than
the high-phytate diet, but the difference was greater if growing pigs rather
than gestating sows were fed. Gestating sows had reduced STTD of phosphorus
compared with growing pigs and growing pigs are likely more affected by phytate
level.

Basically similar story was observed for the retention of phosphorus. Phosphorus
retention by growing pigs fed the low-phytate diet was greater than if they were
fed the high-phytate diet, but the phosphorus retention rate by gestating sows
was not affected by phytate level. Regardless of dietary treatment, gestating
sows had reduced retention of phosphorus compared with growing pigs and the
values were almost zero.

Let me draw some conclusions.

The results from this study tell us that basal endogenous losses of calcium and
phosphorus that were obtained from sows in mid-gestation were greater than the
values from growing pigs.

In spite of greater basal endogenous losses of calcium and phosphorus, gestating
sows still had lower values for STTD and retention of calcium and phosphorus
compared with growing pigs. 

Interactions between physiological state and phytate level for the STTD of
calcium and phosphorus, and calcium and phosphorus retention, were observed and
these results indicate that growing pigs are more likely to be affected by
dietary phytate than gestating sows. 

The take home messages of this presentation are: that it is not accurate if
growing pigs’ STTD values for calcium and phosphorus are used for sows; and that
the effects of phytate level differ between gestating sows and growing pigs.

Thank you for your attention. If you would like to know more about this topic,
or want to learn more about swine nutrition, you can visit our web site at
nutrition.ansci.illinois.edu, or search “Stein” and “pig” on Google. I would
like to thank AB Vista for financial support.