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.