Effects of a novel phytase on phosphorus digestibility in corn-soybean meal diets fed to pigs


Hello. My name is Ferdinando Almeida and I
am a Ph. D. student at the Hans Stein Monogastric Nutrition Laboratory here at the University
of Ilinois. Today, I will be presenting the effects of a novel phytase on phosphorus digestibilty
in corn-soybean meal diets fed to weanling and growing pigs. The outline of this presentation will be as
follows: introduction, objectives, Experiments 1 and 2, overall conclusions from both experiments,
and finally some implications of our research. Swine manure is rich in phosphorus because
most of the phosphorus in organic sources, such as corn and soybean meal, is bound to
the phytate molecule. This figure on the right shows the phytate molecule which is formed
by six carbons (represented in yellow) that can bind up to six molecules of phosphate
(represented in brown, green, and white). Because pigs lack the enzyme that hydrolyzes
the phytate molecule, most of the phosphorus present in organic sources is unavailable
to the pigs. Therefore, inorganic phosphorus in the form of monocalcium phosphate or dicalcium
phosphate needs to be added to the diets to meet the pig’s requirement of phosphorus.
This practice, however, has become expensive, and it is not uncommon to observe an oversupply
of inorganic phosphorus in diets fed to weanling pigs, which is one of the causes for the large
amount of phosphorus excreted in swine manure. For this reason, regulations that limit the
amount of phosphorus that can be applied on the fields have been created. This has led
researchers to find solutions to improve phosphorus utilization by pigs, and consequently reduce
phosphorus excretion. One way of doing it is to add exogenous phytase
to the diets. Phytases are the enzymes responsible for the hydrolysis of the phytate molecule.
During hydrolysis of the phytate molecule, the phosphates that were bound to the molecule
are released into the small intestine, and then they are absorbed by pigs. Commercially
available phytases can be produced from fungi or bacteria, and they are classified as 3-,
5-, or 6-phytases depending on the carbon position where they start the hydrolysis of
the phytate. For example, if a phytase starts the hydrolysis at carbon #3 in the phytate
molecule, this is called a 3-phytase. So, phytases are widely used, as they are an efficient
approach to improve phosphorus digestibility and therefore reduce phosphorus excretion. There are several phytases commercially available
and new phytases are constantly being developed. DSM Nutritional Products has developed a new
phytase called Ronozyme HiPhos. This is a 6-phytase, which is derived from bacteria
and expressed in Aspergillus oryzae. This enzyme is not yet available commercially and
there are no data on the effects of Ronozyme HiPhos on the apparent total tract digestibility
of phosphorus in corn-soybean meal diets fed to pigs. Therefore, the objectives of these experiments
were: first, to test the effects of a novel bacterial 6-phytase on the apparent total
tract digestibility of phosphorus in corn-soybean meal diets fed to weanling and growing pigs;
and second, to determine minimum amounts of phytase needed to optimize the apparent total
tract digestibility of phosphorus. Moving now to Experiment 1… For the materials and methods, we formulated
six corn-soybean meal diets. There was a positive control diet with 0.86% calcium and 0.66%
phosphorus. This diet contained dicalcium phosphate as an inorganic source of phosphorus,
and corn and soybean meal as organic sources of phosphorus. The negative control diet contained
0.48% calcium and 0.36% phosphorus and this diet contained only organic sources of phosphorus:
corn and soybean meal. In addition to these two diets, we formulated four diets that were
the negative control plus four levels of phytase. These levels were 500, 1000, 2000, and 4000
phytase units (FYT)/kg. And once again, the enzyme that we used was Ronozyme HiPhos from
DSM. Forty-eight weanling pigs were used in a randomized
complete block design with eight pigs per treatment. They were placed in metabolism
cases that were equipped with a nipple drinker and a feeder. Water was available at all times
and feed was provided twice daily. These cages were also equipped with a screen that goes
underneath the floor, as shown on this picture on the right, which allowed for the total
collection of feces. For the statistical analysis, we used the
PROC MIXED of SAS, and the model included treatment as a fixed effect, and block as
a random effect. There was no effect of block, and therefore block was removed from the final
model. We also conducted polynomial contrasts in which we compared the positive control
versus negative control diets, and we also tested the linear and quadratic effects of
adding graded levels of phytase to the negative control diet. In addition to that, we conducted
a least squares broken-line analysis to determine the minimum amount of phytase needed to maximize
the apparent total tract digestibility of phosphorus. Looking at the results now… This first graph shows the apparent total
tract digestibility of phosphorus. On the y-axis, we have apparent total tract digestibility
of phosphorus on a percentage basis. The yellow bar represents the positive control diet,
the orange bar represents the negative control diet, the maroon bar represents the negative
control plus 500 FYT/kg, the bright red represents negative control plus 1000 FYT/kg, the dark
green represents negative control plus 2000 FYT/kg, and the bright green represents negative
control plus 4000 FYT/kg. As we expected, the apparent total tract digestibility of
phosphorus was greater in the positive control diet than in the negative control diet — 60
versus 40 percent. We observed that adding graded levels of phytase to the negative control
diet improved the apparent total tract digestibility of phosphorus linearly and quadratically from
40 to 70 percent in the negative control diet plus 4000 FYT/kg. Results from the broken-line analysis indicate
that the apparent total tract digestibility of phosphorus reached a maximum of 68.4% at
a phytase level of 1016 FYT/kg. Now let’s look at Experiment 2. For the materials and methods, we formulated
six corn-soybean meal diets as we did for Experiment 1. With the exception that in Experiment
2, the positive control diet contained 0.79% calcium and 0.56% phosphorus, and the negative
control diet contained 0.58% calcium and 0.33% phosphorus. The levels of phytase added to
the negative control diet were the same as in Experiment 1 — 500, 1000, 2000, and 4000
FYT/kg. For this experiment, we used 24 growing pigs
in a 2-period changeover design. In Period 1, pigs had an initial body weight of 36.2
kg, and in Period 2, pigs had an initial body weight of 47.3 kg. For the statistical analysis, we used the
PROC MIXED of SAS, and the model included treatment and period as fixed effects, while
block was the random effect. There were no effects of period and block, and therefore
they were sequentially removed from the final model. Once again, we used polynomial contrasts
to compare the positive control versus the negative control diets, and we also tested
the linear and quadratic effects of adding graded levels of phytase to the negative control
diet. We also conducted a least square broken-line analysis to determine the minimal amount of
phytase that is necessary to maximize the apparent total tract digestibility of phosphorus. Now, moving on to the results… This graph has the same pattern as the graph
for Experiment 1. The results show that the apparent total tract digestibility of phosphorus
was greater for the positive control diet than for the negative control diet, as we
expected. We also observed that the apparent total tract digestibility of phosphorus was
improved linearly and quadratically as phytase was added to the negative control diet. While
the apparent total tract digestibility of phosphorus for the negative control diet was
40%, the apparent total tract digestibility of phosphorus for the negative control diet
containing 4000 FYT/kg was 72%. Results from the broken-line analysis indicate
that the apparent total tract digestibility of phosphorus reached a maximum of 69.1% at
a phytase level of 801 FYT/kg with no further improvements at any level above 801 and below
4000 FYT/kg. For the overall conclusions, Ronozyme HiPhos
was effective in improving the apparent total tract digestibility of phosphorus in both
weanling and growing pigs. Inclusion levels between 800 and 1000 FYT/kg were able to maximize
the apparent total tract digestibility of phosphorus. Although our objective was not to compare
weanling versus growing pigs, our results showed that the effects of adding graded levels
of Ronozyme HiPhos to corn-soybean meal diets were very similar, which indicates that the
effects of adding this enzyme to corn-soybean meal diets fed to pigs with a body weight
anywhere between 14 and 47 kg should be the same. This observation is in agreement with
the fact that in Experiment 2, there was no effect of period on the apparent total tract
digestibility of phosphorus. And it is also in agreement with previous data published
in 1999 where body weight also had no effect on phosphorus digestibility. For the implications, phytase definitely increases
phosphorus digestibility in corn-soybean meal diets. Ronozyme HiPhos can be effectively
supplemented to corn-soybean meal diets, and we should expect to see an improvement in
phosphorus utilization by pigs as well as a reduction in phosphorus excretion. I would like to acknowledge DSM Nutritional
Products for funding this project and I would like to thank you for your attention. If you
need more information, please visit our website that appears on the screen.

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