Phytase, xylanase in broiler diets studied

Phytase, xylanase in broiler diets studied

*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Modesto, Cal. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 5810 W. 78th St., Suite 200, Bloomington, Minn. 55439, or email [email protected]

Research, as well as practical experience, has shown that adding exogenous phytase enzymes to broiler diets containing phytate-bound phosphorus in plant ingredients is effective in releasing a portion of the bound phosphorus.

The "superdosing" of phytase enzymes at two to three times the recommended level has been shown to release even more of the phytate-bound phosphorus.

However, even at these higher levels of enzyme, considerable amounts of undigested phytic acid still remain. This may be due to some of the phytate being locked away in intact cells, prompting an interest in combining phytase with cell wall-degrading enzymes that may have the potential to synergize the release of phytate-bound phosphorus.

A paper exploring the effect of superdosing a phytase enzyme and possible synergy between phytase and xylanase enzymes was recently published by A. Karimi of the University of Kurdistan, Iran; C. Coto, F. Mussini, S. Goodgame, C. Lu and P. Waldroup of the University of Arkansas; J. Yuan of the China Agricultural University, China, and M. Bedford of AB Vista Feed Ingredients, U.K.

 

Experimental design

The research consisted of two related components. The first component was a 5 x 3 factorial arrangement of treatments (15 experimental diets). Five levels of a phytase enzyme in combination with three levels of a xylanase enzyme were added to a phytate phosphorus-deficient basal diet (0.15% non-phytate phosphorus [nPP]). The effects of these enzyme combinations on growth performance and bone ash were measured.

The five levels of phytase were 0, 500, 1,000, 1,500 and 2,000 phytase units (FTUs) per kilogram of diet (zero, 1X, 2X, 3X and 4X the recommended level, respectively). Each of the five phytase treatments was supplemented with a xylanase enzyme at either 0, 0.1 or 0.2 g/kg of feed (zero, 1X and 2X the recommended level).

The phytase supplement was a preparation of 6-phytase produced by the genetically modified yeast Pichia pastoris (Quantum Phytase 5,000 XT). One FTU of phytase activity was defined as the amount of enzyme that liberates one micromole of inorganic phosphate from sodium phytate at pH 5.5 and 37 degrees C (AOAC International, 2005).

The xylanase product was a preparation of thermal stable endo-1,4-beta-xylanase produced by Trichoderma reesei with a xylanase activity of 160,000 BXU/g (Econase XT 25). A BXU unit was defined as the amount of enzyme that would release 1 micromol of reducing sugar per minute on a birch wood xylan substrate (0.5%) at pH 5.3 under the conditions of the assay. All enzymes were added as granules.

The second component of the research consisted of a series of seven diets ranging in nPP content: 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40% and 0.45%. Initially, two diets were formulated: a low-phosphorus diet (0.15% nPP) and a high-phosphorus diet (0.45% nPP). These two diets were blended in appropriate proportions to create the other five diets. The composition of the two basal diets is shown in Table 1.

The performance and bone ash results from feeding the seven diets were used to develop an equation to estimate the phosphorus equivalency value of each of the enzyme combinations fed in the factorial component of the research.

A total of 735 one-day-old Cobb 500 male broiler chicks were obtained from a local hatchery for use in this research. Each experimental diet was randomly assigned to seven replicate pens of five male chicks in an electrically heated battery brooder. All experimental diets were fed in mash form from 1 to 18 days of age.

The birds were weighed as a group upon arrival and at 18 days of age, which was the termination of the research. Feed consumption was recorded for the calculation of feed conversion. Mortality was recorded daily, and feed conversion data were corrected for the bodyweight of the mortality.

At the conclusion of the study, the right tibia from two randomly selected chicks per pen and toes from all chicks were removed for determination of bone ash. The toes of all chicks were dried for 24 hours at 105 degrees C, and ash was determined on pooled samples of the toes from each pen. Tibia bones were cleaned of adhering tissue, fat was removed by ether and alcohol extraction and the bones were dried. Ash content was determined on pooled samples of the bones from each pen.

 

Results

The performance and ash results for the independent variables of phytase and xylanase are shown in Table 2. There was a significant response to increasing levels of phytase for all of the criteria measured. The largest relative response was to the recommended level of phytase (500 FTU). In addition, there were significant stepwise responses to the higher levels of phytase, in particular for bodyweight and tibia ash.

Table 2 shows that xylanase supplementation to the basal diet at the recommended level did not significantly improve any of the performance parameters. Only tibia ash appeared to be numerically improved. The addition of xylanase at twice the recommended level significantly decreased bodyweight and increased feed conversion. There was no indication that supplementing xylanase to an nPP-deficient diet improved performance or enhanced the response to phytase.

There were no significant interactions between phytase and xylanase, and I have chosen not to show those results.

Table 3 shows the growth performance and ash response to the seven levels of nPP. There were significant responses for all criteria measured. Visual inspection suggests that, in this research, the nPP requirement was approximately 0.35-0.40%.

A standard curve was constructed using the increasing levels of nPP as the independent variable (X) and the related bone ash content values as the dependent variable (Y). The equation generated from the standard curve — Y = -199.63X2 + 196.32X - 3.349 (R-square = 0.909) — was then used to calculate the estimated nPP content of each enzyme treatment based on their respective tibia ash percentages. The specific nPP equivalency contributed by the enzyme was calculated by subtracting the nPP level of the basal diet (0.15%). The calculated percent nPP equivalency values are shown in Table 4.

Phytase supplementation had significant and positive impacts on the mean equivalent nPP values (including the xylanase treatments), as shown in Table 4.

The recommended level of phytase (500 FTU) resulted in a mean nPP equivalent of 0.084%, an incremental increase of 0.068%. Subsequent phytase levels of 2X, 3X and 4X the recommended level resulted in incremental nPP levels of 0.025%, 0.038% and 0.044%, respectively, much smaller than the first (recommended level) addition of phytase. However, the incremental response to subsequent levels of phytase (2X, 3X and 4X the recommended level) is not diminishing and may be increasing.

 

Comment

The mean nPP response to levels of phytase is shown in the Figure, which suggests that, in this research, the maximum response to the addition of phytase had not occurred, even at 4X the recommended level.

At 4X the recommended level of phytase, the nPP equivalent response of 0.191 is still only 73% of the phosphorus in the basal diet that is not nPP (from Table 1; total phosphorus minus nPP [0.41 - 0.15 = 0.26]). That 73% is not far off from 70%, which is frequently suggested as the maximum amount of phytate phosphorus that is released by phytase. At the same time, adding the maximum equivalent phytase response (0.191) to the nPP content of the basal diet (0.15) yields a total of 0.341 nPP, which is close to the level of nPP (0.35-0.40, from Table 3) that appeared to support maximum growth performance.

It must be recognized that this research had three key characteristics that are essential: (1) the phytase enzyme was effective, (2) the basal diet was critically deficient in nPP and (3) there was a high level of phosphorus in the basal diet that was not nPP.

1a. This phytase enzyme may not be as effective in other diets; other phytase enzymes may not be as effective as this phytase enzyme.

2a. To obtain a response to phytase, the basal diet must be deficient in phosphorus; the greater the deficiency, the larger the expected response.

3a. Phytase must have an appropriate substrate to act on.

In this basal diet, 0.26% phosphorus apparently was not nPP phosphorus. This phosphorus was not characterized, but a significant portion was probably phytate phosphorus.

The response to superdosing enzymes will likely be limited by: (1) the effectiveness of the enzyme, (2) the degree of nutrient deficiency and (3) the availability of substrate.

 

The Bottom Line

Under the conditions of this research, phytase supplementation significantly improved performance and continued to improve performance even at superdosing levels 4X the recommended level of addition.

However, the xylanase used did not improve the release of phosphorus.

 

Reference

Karimi, A., C. Coto, F. Mussini, S. Goodgame, C. Lu, J. Yuan, M.R. Bedford and P.W. Waldroup. 2013. Interactions between phytase and xylanase enzymes in male broiler chicks fed phosphorus-deficient diets from 1 to 18 days of age. Poult. Sci. 92:1818-1823.

 

1. Composition and calculated nutrient content of experimental diets

 

Low

High

Ingredient, %

phosphorus

phosphorus

Yellow corn

55.998

 

Soybean meal 48.5%

37.660

 

Poultry oil

2.105

 

Ground limestone

1.712

0.727*

Dicalcium phosphate

0.000

1.702*

Sodium chloride

0.310

 

Sodium bicarbonate

0.370

 

Methionine hydroxy analogue-84

0.322

 

L-threonine

0.036

 

L-lysine

0.170

 

Vitamin premix

0.500

 

Mintrex P Se

0.100

 

Washed sand

0.717

0.000*

Total

100.000

100.000

Nutrient, %

Crude protein

23.42

 

Metabolizable energy, kcal/kg

3,042

 

Calcium

0.85

 

Phosphorus, total

0.41

0.78*

Non-phytate phosphorus

0.15

0.45*

Sodium

0.25

 

Chlorine

0.25

 

Dig. methionine

0.56

 

Dig. methionine plus cystinine

0.86

 

Dig. lysine

1.21

 

Dig. threonine

0.77

 

*Change from low-phosphorus diet; all other ingredients/nutrients were the same.

 

2. Response to levels of phytase and xylanase supplementation, 0-18 days

Phytase, 

Bodyweight,

Feed

Feed

Mortality, 

Toe

Tibia

FTU

g

intake, g

conversion

%

ash, %

ash, %

0

233d

424d

1.84a

56.2a

7.5d

24.2e

500

444c

661c

1.50b

11.4b

9.1c

31.6d

1,000

510b

750b

1.50b

2.9bc

10.2b

34.6c

1,500

536ab

785ab

1.48b

1.0c

10.9a

37.0b

2,000

550a

824a

1.50b

1.9bc

11.1a

40.5a

Xylanase, g/kg feed

0.0

476a

702

1.51b

13.7

9.7

32.9

0.1

457a

690

1.54b

14.9

9.8

34.1

0.2

430b

688

1.64a

15.4

9.8

33.7

a-eMeans within a column without common superscripts are significantly different (P < 0.05)

 

3. Response to levels of non-phytate phosphorus, 0-18 days

nPP,

Bodyweight, 

Feed

Feed

Mortality, 

Toe

Tibia

%

g

intake, g

conversion

%

ash, %

ash, %

0.15

250e

431d

1.73a

57.0a

7.4c

22.2e

0.20

371d

620c

1.64ab

31.4b

8.0b

28.5d

0.25

458c

670c

1.46c

2.9c

9.0b

31.8c

0.30

556b

790b

1.48bc

5.7c

10.5b

35.6b

0.35

636a

899ab

1.42c

0.0c

12.2a

43.3a

0.40

677a

963a

1.42c

0.0c

12.8a

44.6a

0.45

670a

912a

1.40c

2.9c

12.6a

42.9a

a-eMeans within a column without common superscripts are significantly different (P < 0.05).

 

4. Calculated percent non-phytate phosphorus equivalency value of phytase and xylanase

 Phytase level,

-Xylanase level, g/kg diet-

 

FTU/kg diet

0.0

0.1

0.2

Mean

Increment

0

0.000

0.022

0.025

0.016e

 

500

0.081

0.086

0.084

0.084d

0.068

1,000

0.110

0.106

0.111

0.109c

0.025

1,500

0.140

0.150

0.152

0.147b

0.038

2,000

0.178

0.197

0.199

0.191a

0.044

Mean

0.102

0.112

0.114

a-eMeans within a column without common superscripts are significantly different (P < 0.05).

Phytase, xylanase in broiler diets studied
 

 

Volume:85 Issue:31

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