Hello. My name is Laura Merriman, and today I will be discussing research that
was conducted at the University of Illinois Swine Research Farm. The title of
today's presentation is “The requirement for digestible calcium by 100 to 130 kg
pigs."

We know that calcium has many roles in the body. These include structural
support by way of the skeletal system, as well as muscle contraction and nerve
impulses. Within the body, approximately 96-99% of calcium is located within the
bone.

Phosphorus is also very important in the body, serving again for the structural
support of the body by the skeletal system. In addition, phosphorus is important
for energy metabolism, being a major component of our energy currency, ATP, and
enzyme activation via phosphorylation. Approximately 60-80% of the phosphorus in
the body is located in the bone.

It is important to supply the dietary needs of these nutrients. However,
deficiencies of calcium and phosphorus may occur from not only inadequate supply
of these minerals individually but also if an inadequate ratio exists between
dietary calcium and phosphorus.

In the most recent edition of the NRC, which was published in 2012, it was
stated that the ratio between digestible calcium and digestible phosphorus would
be preferred. However, due to a lack of data, recommendations were provided
between total calcium and standardized total tract digestible phosphorus.

The NRC offers guidelines of total calcium at 0.46% and 0.21% for standardized
total tract digestible phosphorus for pigs with a body weight between 100 and
125 kg.  To provide the standardized total tract digestible phosphorus
requirement,

a modelling approach was used where body protein was used to determine a whole
body phosphorus mass.

The amount of standardized total tract digestible phosphorus needed to maximize
phosphorus retention could then be computed from these values.

Then, the total calcium requirements were simply multiplied 2.15 times the
standardized total tract digestible phosphorus. It was not clear, however, how
the 2.15 factor was determined.

Regardless, if we are to be more accurate in our formulation, we must move
towards formulating on a standardized total tract digestible calcium basis. In
our lab, we have determined the digestibility of calcium in inorganic sources,
animal protein sources, and plant sources. Therefore, we can formulate on not
only standardized total tract digestibility of phosphorus but also we can now
formulate for standardized total tract digestibility of calcium. Earlier work in
this lab has determined the standardized total tract digestibility of calcium
requirement by the weanling pig. So the objective of this experiment was to
determine the standardized total tract digestibility of calcium requirement for
the finishing pig between 100 and 130 kg body weight.

To answer our objective, we used 90 pigs with an initial body weight of 100 kg.
Experimental diets were fed for a total of 4 weeks.

For each of the 15 diets, we fed 6 replicate pigs in individual pens. Body
weights and feed disappearance were recorded for the duration of the experiment.

Then, at the conclusion of the experiment, all pig were euthanized at the
University Meat Science Laboratory. Femurs were collected from all pigs.

Our response parameters for this experiment included growth performance (average
daily feed intake, average daily gain, and gain to feed ratio) as well as bone
mineral content described using bone ash, bone calcium, and bone phosphorus.

Here I have outlined the experimental diets. Across the top row, we have the 5
dietary calcium levels, provided on a total calcium basis as well as the
standardized total tract digestible calcium basis. Down the first column, I have
provided the 3 dietary levels of standardized total tract digestible phosphorus.
In total, we can see there were 15 diets, resulting from the 5 calcium levels
and the 3 digestible phosphorus levels.

The current NRC recommendations for calcium and phosphorus are indicated in red
boxes. In the purple colored boxes, the standardized total tract digestible
calcium to standardized total tract digestible phosphorus ratios are provided.

Based off the formulation we used for digestibility of calcium, the NRC
recommendations for digestible calcium to digestible phosphorus ratio would be
1.38:1.

For the statistical methods, responses to calcium and phosphorus were determined
using prediction equations where linear, quadratic, and interaction terms for
calcium and phosphorus were tested.

Now I will move to the results.

First, I will present the results for average daily feed intake. For this
response, only digestible calcium was significant (indicating no main effect of
phosphorus or no interaction between calcium and phosphorus). The prediction
equation was average daily feed intake = 3.6782-1.2722 × digestible calcium.
This graph (and also subsequent graphs) will depict the predicted values
determined using the prediction equation. Across the X axis, I have the 5 levels
of digestible calcium from 0.08 to 0.49.  It is clear that intake decreases with
the addition of calcium carbonate, which was our calcium source.

Next, I have presented the results for average daily gain. Again, we only
observed that calcium (not phosphorus) predicts this response. The prediction
equation was average daily gain = 1.2141 – 0.0635 x  digestible calcium. The
reduction in gain is likely the result of reduced intake.

We were not able to predict the gain to feed ratio using any of our terms for
calcium or phosphorus.

Now I will move to the bone mineral responses. Interestingly, bone ash was
predicted using linear terms for standardized digestible calcium and
standardized digestible phosphorus as well as the interaction between these
terms. However, quadratic responses were not significant. Across the X axis I
still have the 5 levels of digestible calcium. Then, the diets containing 0.11%
digestible phosphorus are presented by a green line, the diets containing 0.21%
digestible phosphorus are presented by a blue line, and the diets containing
0.31% digestible phosphorus are presented by a red line. The bone ash appears to
increase by the addition of dietary calcium. However, the deposition of bone
mineral seems to be limited by the level of digestible phosphorus in the diet.
Therefore, pigs consuming greater levels of phosphorus are able to continue
depositing more bone.

In conclusion, growth performance was only predicted by digestibility of
calcium, not phosphorus.

Furthermore, excess calcium suppresses feed intake, which results in a reduction
of growth performance.

Lastly, the pigs' requirement of calcium to maximize bone responses was greater
than that needed for growth performance.

Based on the results from this experiment, we concluded the following. First,
for the standardized total tract digestible calcium requirement, the pig does
not likely need greater than 0.21% STTD phosphorus.

Next, the requirement for calcium needed to maximize bone ash is greater than
that required to maximize growth performance.

Lastly, there are negative effects on growth performance when adding calcium
above the requirement.

Thank you for listening to my presentation. If you have any questions about this
work or other work conducted by our lab, please visit our website at
nutrition.ansci.illinois.edu.