Hi, I’m Laia Blavi, and I’m a postdoctoral
researcher in the Stein Monogastric Nutrition
Laboratory at the University of Illinois.
Today I will be talking about zinc, calcium
and phosphorus interactions and their consequences
in pig nutrition.
I will start by giving a brief introduction
for calcium, phosphorus and zinc, the nutritional
requirements for them, and their mineral interaction.
Then I will move to talk more in detail about
the two mineral interactions between zinc
and calcium and zinc and phosphorus.
And I will finish with the conclusions for
this talk.
Calcium is located mainly in the bone.
Its main functions are to support the skeleton,
muscle contraction, and nerve impulses.
Calcium is a type 1 nutrient.
Phosphorus is also mainly located in the bone,
with concentrations of 60 to 80% there, the
rest being in soft tissue.
Its main functions are also to support the
skeleton, and assist in energy metabolism
and energy activation.
But it is a type 2 nutrient.
Zinc is mainly located in the body cells and
its three main functions are to act as an
enzyme catalyst, regulate gene expression
and act as a structural component.
Zinc is a type 2 nutrient.
So, what does it mean to be a type 1 or 2
nutrient?
Type 1 nutrients are required for specific
functions but type 2 nutrients are required
for general metabolism.
So, when there is a deficiency of a type 1
nutrient, like calcium, the animal continues
growing, but there is a reduction in the body
stores of this mineral and also a reduction
of its functions.
But in zinc or phosphorus deficiency the pig
reduces growth to try to maintain the tissue
concentration of the nutrient and there is
also a reduction of the endogenous losses
and a decrease in the appetite.
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 requirements of total phosphorus are 0.60%
and the digestible phosphorus are 0.33%.
However, most of the phosphorus in the swine
diets is bound to phytate and therefore we
have to supplement the diets with phytase
or inorganic phosphorus like monocalcium phosphate
or dicalcium phosphate.
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.
However, zinc is inert and non-degradable
in the manure and in the environment.
so the long-term application of swine manure
and broiler litter increases the concentration
of zinc in the soil.
In this graphic we can observe the concentration
of zinc in Europe; red indicates higher concentration
of zinc.
When we compare the graphic with the pig production
in Europe, we can observe that the zones with
higher pig production, like Denmark, are also
the zones with higher zinc concentration.
This concentration of zinc in the soil can
produce environmental pollution, can reduce
crop yields, and it’s also a risk for aquatic
animals.
Another problem of feeding therapeutic levels
of zinc oxide to pigs is the development of
antibiotic resistant bacterial strains.
This phenomenon has been observed in multi-resistant
E. coli and methicillin-resistant Staphylococcus
aureus.
Another disadvantage of using high doses of
zinc is the interactions between minerals.
However, not all mineral interactions are
always negative.
We can find synergism between elements, which
is when two or more mineral elements mutually
enhance their absorption in the digestive
tract and jointly fulfill some metabolic functions
at the tissue or cell level.
For example, calcium and phosphorus in the
formation of bone hydroxyapatite, or iron
and copper in the formation of hemoglobin.
However, I will focus on the antagonism effect.
The antagonism interaction is when two or
more minerals inhibit the absorption of each
other in the digestive tract and produce opposite
effects on biochemical functions in the organism.
For example, zinc and copper inhibit the absorption
of each other in the intestine.
Now I will move on to the first mineral interaction,
zinc and calcium.
Zinc competes with calcium for absorption
through channel proteins on the brush border
membrane in the small intestine.
However, this transporter has greater affinity
for zinc than for calcium.
In 1956, it was observed that when calcium
levels are increased in a diet with low dietary
zinc, the incidence of parakeratosis was increased
dramatically.
It has also been observed that high calcium
levels in the diet reduce zinc bioavailability:
in rats and catfish, reducing the bone zinc
concentration; in poultry, reducing the plasma
zinc concentration; and in pigs, reducing
the blood and bone zinc concentration.
Also it was observed that phytate reduced
zinc bioavailability.
High dietary zinc level reduces calcium bioavailability.
A reduction of calcium was observed when weanling
pigs were fed 3,000 ppm of zinc oxide in diets
without phytase supplementation.
However, in another experiment, the addition
of therapeutic doses of zinc did not reduce
the calcium digestibility, but when diets
were supplemented with 2,500 FTU of phytase,
high levels of zinc reduced the apparent calcium
digestibility.
In growing pigs, the inclusion of increasing
doses of zinc oxide did not reduce the apparent
total tract digestibility of calcium.
Pigs were fed a diet based on barley, wheat
and soybean meal and supplemented with 1,000
FTU of phytase.
In one of our experiments carried on at the
University of Illinois, we tested the supplementation
of therapeutic doses of zinc oxide and the
addition of phytase in diets fed to growing
pigs.
We observed that the addition of phytase increased
the standardized total tract digestibility
of calcium, but it was less if zinc oxide
was added to the diets.
There was no interaction between zinc oxide
and phytase, meaning that the increased digestibility
of calcium that was caused by phytase is independent
of the concentration of zinc in the diet.
In the same experiment but instead measuring
the calcium retention, we observed the same
results as in the standardized total tract
digestibility of calcium but there was an
interaction between zinc oxide and phytase.
In pigs fed no zinc oxide, the addition of
3,000 FTU of phytase increased the calcium
retention compared with 1,000 FTU of phytase.
However, with the addition of zinc oxide there
was no difference.
This could be explained by multiple mineral-phytase
complexes being more stable than single mineral
complexes.
Also, calcium and zinc act together to increase
phytate precipitation.
So high dietary zinc increases the negative
effect of phytate on calcium digestibility
and this may reduce the standardized total
tract digestibility of calcium.
Since calcium and zinc compete for a common
transport pathway and the transport has more
affinity for zinc, another hypothesis might
be that high levels of zinc oxide increase
the possibility of zinc being absorbed and
reduces the capacity of calcium to be transported.
So at the end, it may be a reduction of the
absorption and digestibility of calcium.
Now I will focus on the interaction between
zinc and phosphorus.
Most of the phosphorus is bound to phytate:
in cereal seeds, between 59 and 70%; in legume
seeds, between 20 to 46%; and in oilseed meals,
between 34 to 66%.
Zinc is a potent inhibitor of phytate-phosphorus
hydrolysis by phytases.
It seems that zinc binding causes a conformational
change in the phytate moiety.
As a consequence, phosphorus will be less
accessible to phytase.
In weanling pigs fed low levels of phosphorus,
the addition of 3,000 ppm of zinc oxide reduced
the average daily gain.
These diets contained phytase.
However, when pigs were fed the recommended
levels of phosphorus and without phytase,
the addition of 3,000ppm of zinc oxide did
not reduce the average daily gain.
In the same study they also observed that
the addition of 3,000 ppm of zinc oxide to
weanling diets with low levels of phosphorus
and with phytase reduced the levels of phosphorus
in plasma.
But in diets with recommended levels and without
phytase, the addition of 3,000 ppm of zinc
oxide did not decrease the phosphorus plasma
levels.
In another study with weanling pigs and chicks,
the supplementation of high levels of zinc
in low phosphorus diets with phytase reduced
the fibula ash in pigs and the tibia ash in
chicks, which is an indirect measure of phosphorus
bioavailability.
Also in growing pigs, the supplementation
of therapeutic levels of zinc in low phosphorus
diets with phytase reduced the apparent total
tract digestibility of phosphorus.
In weanling pigs, the addition of graded levels
of zinc oxide linearly reduced the phosphorus
digestibility when diets were formulated within
the recommended phosphorus levels; however,
with higher levels of phosphorus, there were
no effects of adding zinc oxide to the diets.
In another study in weanling pigs fed diets
with recommended phosphorus levels, pharmacological
concentrations of zinc oxide decreased plasma
phosphorus, regardless of phytase supplementation.
In our lab, we observed that pigs between
15 to 20 kg and fed diets with the recommended
phosphorus levels, phosphorus retention increased
as the concentration of phytase increased
in the diet, but the increase was greater
if zinc oxide was not added than if zinc oxide
was added into the diets.
The last example that I will talk about is
weanling pigs fed diets with recommended phosphorus
levels and without phytase.
It was observed that the supplementation of
1,750 ppm of zinc reduced the apparent total
tract digestibility of phosphorus.
To conclude, mineral interaction is a complex
world and not all interactions are negative.
In zinc and calcium interaction, we observed
that both high calcium and zinc levels reduce
the bioavailability of the other.
In zinc and phosphorus interaction, high levels
of zinc will reduce phosphorus availability
in diets with low levels of phosphorus and
also in diets with recommended levels of phosphorus,
but not in diets with higher phosphorus levels.
So, if pigs require pharmacological levels
of zinc we should increase dietary concentrations
of calcium and phosphorus or supplement with
phytase.
And with that, I would like to thank my fellow
lab members.
If you enjoyed this presentation and 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.
