Hi. My name is Caroline González-Vega, and I recently completed my PhD work with
Dr. Stein at the University of Illinois. And today I have the pleasure to talk
about the digestible calcium requirements for 25-50 kg pigs.

The objective of this study was to determine the requirement for standardized
total tract digestible calcium needed to maximize average daily gain, gain:feed
ratio, bone ash, calcium retention, at different concentrations of standardized
total tract digestible phosphorus.

For this study, we used 20 diets. We had five different concentrations of total
calcium, from 0.18 to 1.14%, which corresponds from 30-170% of the NRC
requirement.

These diets were based on corn, soybean meal, calcium carbonate, and monocalcium
phosphate. And because we previously determined the standardized total tract
digestibility of calcium in these ingredients, we were able to calculate the
standardized total tract digestible calcium in these diets. These values ranged
from 0.13 to 0.72%.

We have also four different concentrations of standardized total tract
digestible phosphorus, from 0.15 to 0.47%, which corresponds from 50-150% NRC
requirement.

These are the standardized total tract digestible calcium and standardized total
tract digestible phosphorus ratios of the diets. It ranged from 0.28:1 to 4.8:1.
The NRC requirement of calcium for the 25-50kg pigs is 0.66%, and the NRC
requirement of standardized total tract digestible phosphorus is 0.31%, which
corresponds to a ratio standardized total tract digestible calcium and
standardized total tract digestible phosphorus of 1.35:1.

The same batch of diets were used for two different experiments. One experiment
was a growth performance study that was conducted in 28 days, and we had two
pigs per pen: one gilt and one barrow. On day 28, barrows were slaughtered to
collect the right femurs to measure bone ash. The second experiment was a
balance study. Pigs were housed individually in metabolism cages for 13 days,
and fecal and urine samples were collected using the marker-to-marker approach.

Now, let's move into the results. This is a response surface model of the 20
diets. On the x axis, we have the concentration of standardized total tract
digestible calcium, on they axis we have the variable, the red line represents
the diets containing 0.15% digestible phosphorus, the black line represents the
diets containing 0.31% digestible phosphorus, the blue line represents the diets
containing 0.39% digestible phosphorus, and the green line represents the diets
containing 0.47% digestible phosphorus.

From this slide, we can observe that at low concentrations of standardized total
tract digestible calcium, the average daily gain was not very affected by the
concentration of standardized total tract digestible phosphorus.

However, if diets contained 0.42% digestible calcium, there was a negative
effect on the average daily gain for the diet containing 0.15% digestible
phosphorus. But little difference was observed for the diets containing 0.31,
0.39, and 0.47% digestible phosphorus.

If diets contain high concentrations of calcium, it results in an advantage to
have more digestible phosphorus in the diets to reduce the negative effect on
the average daily gain.

On the right, we observe the pigs that were fed the diets containing 0.47%
digestible phosphorus. And on the left, we have the pigs that were fed diets
containing 0.15% digestible phosphorus. So you can see the difference in the
body weight gain.

This is the gain:feed ratio. And here we observed that at low concentration of
digestible calcium, the gain:feed ratio was not very affected by the
concentration of digestible phosphorus.

However, if diets contained 0.42% digestible calcium, we observe a negative
effect on the gain:feed ratio for the diets containing 0.15% digestible
phosphorus. But little difference was observed for the diets containing 0.31,
0.39, and 0.47% digestible phosphorus.

If diets contain) high concentrations of calcium, it results in an advantage to
have more digestible phosphorus in the diets to reduce the negative effect on
the gain:feed ratio.

This is the bone ash in grams. And at low concentration of calcium, we observed
that bone ash was not very affected by the concentration of digestible
phosphorus.

However, if diets contained 0.42% digestible calcium, the bone ash was
negatively affected in diets containing 0.15% digestible phosphorus. But little
difference was observed for the diets containing 0.31, 0.39, and 0.47%
digestible phosphorus.

If diets contain high concentrations of calcium, it results in an advantage to
have more digestible phosphorus in the diets to reduce the negative effect on
the bone ash.

This is the retention of calcium in the body. And we observed that there is no
difference at low concentrations of digestible calcium regardless of the
digestible phosphorus concentration.

If diets contain 0.42% digestible calcium, we start to see a difference in the
retention of calcium, and it increased as we increased the digestible phosphorus
concentration.

But at high concentrations of digestible calcium, it results in greater
retention of calcium if we have greater concentrations of digestible phosphorus.

This is a summary of the digestible calcium:digestible phosphorus ratio needed
to maximize average daily gain, gain:feed ratio, bone ash, and calcium retention
at the difference concentrations of digestible phosphorus.

To maximize growth performance, we recommend if diets are formulated containing
from 0.31 to 0.47% digestible phosphorus, to use a digestible calcium:digestible
phosphorus ratio between 1.16:1 and 1.43.1.

For bone ash, a greater digestible calcium:digestible phosphorus ratio is
needed. It ranged from 2.87:1 to 1.47:1. For calcium retention, the digestible
calcium:digestible phosphorus ratio is greater than the ratio needed to maximize
bone ash. This ratio ranged from 5.07:1 to 2.36:1.

It has been reported that the calcium:phosphorus ratio in the empty body weight
of 50kg pigs is between 1.25:1 and 1.70:1. We see that these ratios were similar
to the ratios needed to maximize bone ash when pigs were fed between 0.31 and
0.47% digestible phosphorus.

In conclusion, digestible calcium:digestible phosphorus ratio needed to maximize
calcium retention is greater than the ratio needed to maximize bone ash.

But further research needs to be conducted to elucidate where the extra calcium
is being deposited if it's not in the bones.

The digestible calcium:digestible phosphorus ratio needed to maximize bone ash
is greater than the ratio needed to maximize growth performance.

And we have to take into consideration that these greater ratios will negatively
affect the growth performance.

Therefore, the digestible calcium:digestible phosphorus ratio needed to maximize
growth performance: If the digestible phosphorus is below the requirement by
NRC, these ratios should be between 0.60:1 and 0.80:1.

But if the digestible phosphorus meets or exceeds the NRC requirement, the
digestible calcium:digestible phosphorus ratio should be between 1.16:1 and
1.43:1.

The implications of this study are that diets fed to pigs should be formulated
based on digestible calcium and digestible phosphorus. And to optimize growth
performance, diets should contain digestible calcium:digestible phosphorus ratio
between 1.15:1 and 1.45:1.

Thank you for your attention. And also, we want to acknowledge AB Vista for
their financial support. And if you want to see more about this research or
other related topics, you can visit our website: nutrition.ansci.illinois.edu.
Thank you again. Bye.