Hi, I’m Laia Blavi, and I’m a postdoc researcher in the Stein Monogastric
Nutrition Laboratory of the University of Illinois. And today I will be talking
about the effects of zinc oxide and microbial phytase on the digestibility of
calcium and phosphorus in maize-based diets fed to growing pigs. For this
presentation, I will start by giving a brief introduction on the nutritional
requirements for minerals in weanling pigs and also I will talk about the
mineral interaction. And then I will move to the materials and methods, and then
dive into the results and discussion for this experiment, before drawing
conclusions and then giving a take home message.

The nutritional requirements for calcium of a pig between 11 to 25 kg are 0.70%.
The problem is that swine diets are based on plant sources that have low calcium
concentration, and therefore, we have to supplement them with inorganic sources
like calcium carbonate or animal sources like meat or bone meal.

The nutritional requirements for zinc are around 100 ppm, but it can be used
therapeutically up to as much as 3,000 ppm of zinc oxide to prevent the
post-weaning diarrhea and to promote growth performance.

So, often we are adding high levels of zinc and calcium to post-weaning diets.
But zinc and calcium show an antagonistic interaction, meaning that they inhibit
the absorption of each other. This is because they are chemically similar and
share similar absorption mechanisms. It has been observed that zinc can compete
with calcium for absorption through channel proteins on the brush border
membrane in the small intestine. And also, zinc and phosphorus show an
antagonistic interaction. Therefore, it is possible that elevated levels of
dietary zinc can interfere with the absorption of calcium and phosphorus.

We also have to take into consideration that piglets have low acid secretion and
after weaning the diets contain low levels of lactose, that is the principal
source of acidity by bacterial fermentation. Moreover, diets containing calcium
carbonate and zinc oxide have higher acid binding capacity, also called
buffering capacity, that is, the ability to neutralize any feed acidity. Taking
all these together, increases in the digesta pH can decrease the phytate
solubility and also the activity of phytase.

Calcium and zinc may bind to phytate which can decrease calcium absorption.
However, nowadays we can use phytase, an enzyme that hydrolyzes the
phosphomonoester bonds of phytate, and thus may increase the digestibility of
phosphorus and calcium. However, possible interactions between zinc and phytase
on the standardized total tract digestibility of calcium have not been reported.

So, the hypothesis of this experiment was to test if pharmacological levels of
zinc affects apparent total tract digestibility of calcium and phosphorus and
standardized total tract digestibility of calcium. And whether microbial phytase
increases the ATTD and STTD of calcium and the ATTD of phosphorus regardless of
the concentration of zinc in the diet.

A total of 56 growing barrows between 15 to 20 kg were allotted to a randomized
complete block design. We used 7 diets, so we had 8 replicates per diet. 

One diet was a diet free of calcium to determine the basal endogenous losses of
calcium and the other 6 diets were the dietary treatments that followed a 3 by 2
factorial, where the main factors were phytase and zinc. The levels of phytase
were 0, 1,000, or 3,000 FTU of phytase and the levels of zinc were 0 or 3,000
ppm of zinc oxide. The phytase that we used for the experiment was Quantum Blue,
of ABVista.

The total experiment lasted 13 days, where the first 5 days were the adaptation
period to adapt the piglets to the diet and to the metabolic cages. 

The diet was offered to the pigs twice a day. On day 6, the first marker, indigo
carmine, was added to the diets and for 5 consecutive days the feces, urine and
the orts were collected. We started to collect the feces when they turned blue.
At day 11, we added the second marker, ferric oxide, and we collected feces
until red appeared.

The experimental diets were based on corn. In this table we can see how the
calcium free diet had no calcium carbonate addition, and the diets with
therapeutic levels of zinc had 0.3% of zinc oxide. 

For the analyzed composition, the calcium free diet had negligible traces of
calcium. Zinc, phosphorus and phytase values were in agreement with the
calculated values.

Moving to the results, I will start with calcium. All the following results
slides will have the same format. In this graphic, we have the apparent total
tract digestibility of calcium. On the X axis there are the 6 dietary
treatments. The first three bars, the orange ones, are the diets without zinc
oxide addition; and the last three, the blue ones, are the diets with zinc
oxide. In each group of diets, with zinc oxide or without zinc oxide, there are
the three levels of phytase: 0, 1,000 and 3,000 FTU of phytase. The Y axis
represents the percentage of apparent total tract digestibility of calcium. 

The ATTD of calcium increased as the concentration of phytase increased, as
signified by the pink arrows, but it was lower when zinc oxide was added to the
diets than when no zinc oxide was added. The red arrow represents the mean ATTD
of calcium without zinc oxide and with zinc oxide.

The standardized total tract digestibility followed the same pattern as ATTD,
where the digestibility increased as the concentration of phytase increased and
it was lower when zinc oxide was used than when no zinc oxide was added.

Calcium retention takes into account the urine losses of calcium. Pigs fed the
diets with 3,000 FTU and without zinc oxide had greater calcium retention than
pigs fed the diets with 1,000 FTU and without zinc oxide. However, in pigs fed
the diets with zinc oxide there were no differences between the addition of
3,000 and 1,000 FTU of phytase.

The percentage of apparent total tract digestibility of phosphorus increased as
the concentration of phytase increased in the diets, represented by the pink
arrow, but it was lower when zinc oxide was added into the diets than when no
zinc oxide was added. 

The results of phosphorus retention, which takes into account the urine
phosphorus losses, also followed the same pattern. The percentage of phosphorus
retention increased as the concentration of phytase increased in the diets. We
can see in this graphic that the bars with 3,000 FTU are greater than the bars
with 1,000 FTU. But this increase was lower when zinc oxide was added into the
diets.

So, to conclude, pharmacological levels of zinc in the diets reduced calcium and
phosphorus digestibility. But the addition of 1,000 FTU of microbial phytase
ameliorates this negative impact. And 1,000 FTU of microbial phytase increased
the ATTD and STTD of calcium and the ATTD of phosphorus.

Finally, the take home message of this presentation is that if pigs require
pharmacological levels of zinc, we can either increase dietary concentration of
calcium and phosphorus or we can supplement the diets with phytase.

And with that, I would like to thank my fellow lab members. Without their help,
this experiment would not have been possible. If you enjoyed this presentation
and you would like to know more about this topic, or want to learn more about
nutrition, you can visit our web site at nutrition.ansci.illinois.edu. Thank you
for your attention.