Hello everyone, my name is Su A Lee from the University of Illinois. 
Today, we will discuss the effects of increasing a novel phytase in diets on digestibility of minerals and energy in pigs.

Traditional diets for pigs in the US mainly contain corn and soybean meal.
In most plant-based feed ingredients including corn and soybean meal, significant amounts of P are phytate-bound.
The concentrations of P in corn and SBM are 0.26 and 0.81%, respectively, but as mentioned earlier, about 81% of P is phytate-bound in corn and is 47% in SBM.
Phosphorus bound to phytate may be released by the enzyme phytase, but pigs secrete very limited quantities of phytase.
Therefore, pigs are not able to release most of the phytate-bound P in feed ingredients, which is the reason they have low digestibility of P. 
This thus will bring negative economical impact on economics and the excess excretion of P may increase environmental pollution.
To increase the P utilization, several strategies may be used. 
Feed processing technology including heat treatment or distillery processes may increase P utilization.
We can also use transgenic pigs that are able to secrete enough phytase in saliva to utilize P from phytate or transgenic plants that contain low phytate-P or high intrinsic phytase.
However, the first two may not be the most-used methods for increasing P utilization in the swine industry in the US.
To increase P utilization in diets for pigs, calcium phosphates are used because digestibility of P in the feed phosphates are much higher than in plant- based feed ingredients.
Lastly, exogenous phytase is commonly used in commercial diets to increase digestibility of P from phytate in plant-based feed ingredients, which reduces the need for feed phosphate in diets and also results in reduced excretion of P in the manure.
Superdosing phytase in diets may also increase digestibility of nutrients such as amino acids and other minerals, even though they are not the substrates for phytase
Here are the possible mechanisms with exaggerating animations.
Phytate is negatively charged in the gastrointestinal tract of pigs.
Because of the negatively charged reactive sites on the phytate molecule, chelated mineral-phytate or nutrient-phytate compounds may precipitate in the intestinal tract.
However, phytase hydrolyzes the ester bonds and thus releases the chelated nutrients, which results in increases in digestibility.

Another hypothesis is that before nutrients get to bind to phytate molecules, 
phytase hydrolyzes the ester bonds to prevent them  to chelate, which also increases digestibility of P and other nutrients
In this experiment, a novel E. coli phytase was used. This phytase starts the hydrolysis at position C6 of the inositol ring.
Even though the phytase is non coated, this phytase is heat stable.
This phytase is also unique in that the production efficiency is higher than other phytase. 
The objective of this experiment was, therefore,  to test the hypothesis that increasing phytase in corn-SBM based diets increases the apparent total tract digestibility, ATTD, of energy, the standardized total tract digestibility, STTD of P, and the ATTD of minerals.
For this experiment, 48 pigs with the initial body weight of 22.6 kilos were utilized and they were fed 6 diets to have a total of 8 replicates per diet.
All diets contained corn and soybean meal.
The first diet was the positive control diet that contained P at the requirement for standardized total tract digestible P by 11 to 25 kg pigs.
The second diet was the negative control diet that was similar to the positive control diet with the exception that no feed phosphates were used. 
Four additional diets that were similar to the negative control diet were formulated to contain 250, 500, 1,000, or 2,000 unit of phytase per kg of diet.
 Therefore, there were 5 negative control diets. 
Fecal samples were collected quantitatively for 4 days after 5 days of adaptation. 
Fecal samples were dried and ground to be analyzed for dry matter, gross energy, phosphorus, and other minerals.
After feed intake, fecal excretion, and the digestibility values were calculated, data were analyzed using mixed procedure of SAS.
The model included diet as the fixed variable and group as the random variable.
Contrast coefficients were used to compare the positive and negative control diets and linear and quadratic effects of increasing phytase in the negative control diets.
Moving on with the results, let me set up the slides.
In the X axis, we have the positive control diet and the 5 negative control diets with increasing phytase from 0 to all the way up to 2,000. Here in the y-axis we will have response parameters, and all the next graphs will have the same structure
The ATTD of dry matter in the negative control diet containing no phytase was greater compared with the positive control diet. This can be explained with the diet formulation that the positive control diet contained more feed phosphates than the negative control diet, which may reduce the dry matter digestibility.
However, there was no effect of increasing levels of the novel phytase on the ATTD of DM in the negative control diets.
We also determined the ATTD of gross energy and digestible energy in diets.
And the results indicated that the ATTD of gross energy in the positive control diet was less than in the negative control diet when no phytase was used. The reason for the reduction can also be explained by the fact that feed phosphates contain no energy and the negative control diet does not contain any feed phosphate.
Similar to the ATTD of dry matter, we did not observe the effect of increasing phytase on the ATTD of energy in the negative control diets.
Because the ATTD of energy increased, the concentration of digestible energy in the negative control diet was greater than in the positive control diet when no phytase was used. There was no effect of phytase on the concentrations of digestible energy in the negative control diets.
This slide shows the STTD of P in percent. 
The results from this experiment indicated that the STTD of P in the positive control diet was greater than in the negative control diet when no phytase was used. This observation demonstrated that use of feed phosphate in the positive control diet increased the digestibility of P compared with negative control diet.
Increasing levels of phytase from 0 to 2,000 units quadratically increased the STTD of P in the negative control diets
This result indicated that the novel phytase was able to break down the ester bonds between phosphorus and the inositol ring of phytate and thus increased digestibility of P.
This slide shows the ATTD of Ca in percent and the ATTD of Ca in the positive control diet was greater than in the negative control diet without phytase, which was also the result of using DCP in the positive control diet.
Increasing levels of phytase from 0 to 2,000 units quadratically increased the ATTD of Ca in the negative control diets, which is not a surprise to us. It is well known that phytase increases digestibility of Ca because use of phytase releases Ca from Ca-phytate complex or prevents the complex formation. Based on this, it is important that the release of both Ca and P by phytase should be considered in diet formulation. 
This slide shows the ATTD of Mg in percent.
The ATTD of Mg was not different between the positive and negative control diets, but the ATTD of Mg increased linearly as phytase increased in the negative control diets. 
However, under the condition of this experiment, we did not observe any effects of dietary Ca and P or increasing phytase in diets on the ATTD of potassium, sodium, cooper, iron, manganese, and zinc. It has not been conclusively demonstrated that phytase also increases digestibility of minerals other than P and Ca in diets fed to pigs and inconsistent results among experiments have been reported. In this experiment only digestibility of Mg was increased by phytase, but we do not have any explanation why only Mg was influenced.
In conclusion, the ATTD of dry matter and gross energy was lower in the positive control diet compared with the negative control diet because of the use of feed phosphate.
The use of feed phosphate increased the digestibility of P and Ca in the positive control diet than in the negative control diet.
Increasing phytase from 0 to 2,000 unit per kg of diet increased the digestibility of P, Ca, and Mg. However, the ATTD of energy, dry mater and other minerals was not changed. 
With that, we would like to acknowledge Hanley international for their valuable inputs and financial support. 
Thank you for your interest in this presentation. 
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