Effect of calcium carbonate particle size on ATTD and STTD and retention of calcium by growing pigs


Hello, my name is Laura Merriman. I am a PhD
student in Dr. Stein’s laboratory. Today, I will be discussing an experiment I conducted
in the summer of 2014 at the University of Illinois Swine Research Farm. The title of
my presentation is “The effect of particle size of calcium carbonate on apparent and
standardized total tract digestibility and retention of calcium by growing pigs.” The outline for this presentation will go
as follows. First, I will briefly discuss the background
regarding the particle size of calcium carbonate. Then, I will describe the materials and methods
of the experiments. Then, I will present the results for the apparent total tract digestibility,
standardized total tract digestibility, and retention of calcium. This will be followed
by results for the apparent total tract digestibility and retention of phosphorus. And then, I will
leave you with some conclusions and a take home message. It has been observed that the particle size
of calcium carbonate impacts calcium metabolism differently according to animal species. For
example, in mice and ruminants, the particle size of calcium carbonate does not influence
the digestibility of calcium carbonate. However, in poultry, reducing the particle size of
calcium carbonate does influence calcium metabolism. In hens, it is important to include larger
particle sizes to provide a calcium reserve in the gizzard during overnight fasting to
allow for egg formation. In contrast, broiler chicks optimize calcium digestibility, bone
strength, and bone ash when smaller particle sizes of calcium carbonate are provided in
the diet. The only data available on the particle size
of calcium carbonate fed to pigs comes from Ross and coworkers in 1984. They evaluated
the relative bioavailability of calcium carbonate at various particle sizes, and observed no
differences. However, to our knowledge, no data are available for the digestibility of
calcium carbonate among diets containing calcium carbonate ground to different particle sizes. Therefore, the objective of this experiment
is to determine the effect of particle size of calcium carbonate on apparent total tract
digestibility, standardized total tract digestibility, and retention of calcium fed to growing pigs. For this experiment, calcium carbonate was
ground to 4 different particle sizes. They include 200, 500, 700, and 1125 microns. Here
I have illustrated the smallest particle size at 200 micros, and the largest particle size
at 1125 microns. To test our hypothesis, we conducted a metabolism
experiment using 40 growing barrows with an initial body weight of 15.42 kg. Barrows were
randomly allotted to a randomized complete block design with initial body weight as a
blocking criteria. Barrows were randomly allotted to one of six dietary treatments. These barrows
were individually housed in metabolism cages. They were provided five days to adapt to their
diets and environments. Following the adaptation, total urine and feces were collected for five
days. Total feces were collected using the marker
to marker approach. On day 6 of the experiment, indigo carmine was added to the morning diet
to indicate passage of the ingested material. Then on day 11 of the experiment, ferric oxide
was added to the morning meal to indicate the ending of collection. Total urine volume was also reported. A 20%
subsample was collected, mixed, and then subsampled. At the beginning of each daily collection
period, 50 ml of 6N HCL was added to the urine pail and used as a preservative. In this experiment, feces and urine samples
were analyzed for calcium and phosphorus. Diets were analyzed for calcium and phosphorus
in addition to dry matter, crude protein, ash, gross energy, ADF, and NDF. For this experiment, we used calculations
from the NRC. The apparent total tract digestibility, as a percentage, was calculated as (calcium
intake minus calcium feces) divided by calcium intake and multiplied by 100. The standardized total tract digestibility,
expressed as a percentage, was calculated as (calcium intake minus calcium feces minus
basal endogenous calcium losses) divided by calcium intake and multiplied by 100. Retention, expressed as a percentage, was
calculated as (calcium intake minus calcium feces minus calcium urine) divided by calcium
intake and multiplied by 100. Similar equations were also used for the apparent
total tract digestibility and retention of phosphorus. The composition of the diets is as follows.
These diets were corn and potato protein based diets. Corn was included at 75.6% of the diet
and potato protein was included at 18% of the diet. Our primary source of phosphorus
in the diet came from monosodium phosphate, and that was included at 0.98% of the diet.
Calcium carbonate was included at 1.73% of the diet. In addition, about 4% of the diet
came from other ingredients including soybean oil, salt, and our vitamin and mineral premix. The calcium carbonate included in the diet
was either ground to 200, 500, 700, or 1125 microns for each respective experimental diet. Additionally, a calcium free diet was formulated
and calcium carbonate was replaced by corn. The nutrient composition of the diet is as
follows. Calcium was formulated at 0.70%, standardized digestible phosphorus was formulated
at 0.33%, and lysine was formulated at 1.4%. For the statistical analyses, we used the
mixed procedure of SAS. The experimental unit was the pig. We had a fixed effect of diet
and a random effect of replicate. Linear and quadratic statements were also included in
our model. Statistical significance was observed when P values were less than or equal to 0.05.
and trends were observed when P values were greater than 0.05 but less than or equal to
0.1. Now let’s move to our results. First, I would like to orient you to this
graph, as the subsequent graphs will follow the same format. Across the x axis we have
our experimental diets, with the red bar indicating the diet containing calcium carbonate ground
to 200 microns, the yellow bar indicating the diet containing calcium carbonate ground
to 500 microns, the blue bar indicating the diet containing calcium carbonate ground to
700 microns, and the green bar indicating the diet containing calcium carbonate ground
to 1125 microns. Here I am presenting the apparent total tract
digestibility of calcium, expressed as a percent. We observed no difference among our dietary
treatments, with values ranging from 70 to 74. Next, I have the standardized total tract
digestibility of calcium, expressed as a percent. We observed no difference among our dietary
treatments, with values ranging from 74 to 78. Here I have presented the retention of calcium,
expressed as a percent. Again, we observed no difference among our dietary treatments,
with values ranging from 64 to 70. Now, I will switch gears and discuss results
for phosphorus. There were no differences among dietary treatments for the apparent
total tract digestibility of phosphorus, expressed as a percent, with values between 63 and 67. Finally, there were no differences in the
retention of phosphorus, expressed as a percent, with values ranging from 61 to 64. In regards to the digestibility of calcium
in diets containing calcium carbonate ground to different particle sizes, pigs are not
different from mice and ruminants. They are different, however, from poultry. We believe
that poultry are the unique species here. This may be due to the differences in transit
time of digesta and/or the presence of the gizzard. Also, it is important to note that in pigs,
most calcium is absorbed in the stomach and proximal duodenum. Therefore, if differences
existed in the early absorption due to particle size, the pig would have more opportunities
to absorb the calcium further down the intestinal tract. In conclusion, the apparent total tract digestibility,
standardized total tract digestibility, and retention of calcium was not influenced by
particle size of calcium carbonate. Furthermore, the apparent total tract digestibility and
retention of phosphorus was not influenced by particle size of calcium carbonate. The take home message for today’s presentation
is that calcium carbonate can be included over a broad range of particle sizes without
impacting the digestibility of calcium and phosphorus. I would like to thank the Iowa Limestone Company
for supporting this project. If you have any questions about this presentation
or other presentations conducted in our swine nutrition laboratory, please visit our website
at nutrition.ansci.illinois.edu. And thank you for listening to my presentation today!

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