Digestibility of phosphorus in enhanced torula yeast and fish meal fed to weanling pigs

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An enhanced torula yeast was recently developed as a natural alternative protein source to fish meal and other animal proteins. This ingredient has a lower carbon footprint than other available yeast proteins because it is derived from forestry by-products. The enhanced torula yeast has an improved amino acid (AA) profile, a greater digestibility of AA than fish meal, and an energy value that is not different from that in fish meal. However, there are no data available about the digestibility values of P in this new ingredient. Therefore, an experiment was conducted to test the hypothesis that the values for apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in enhanced torula yeast are not different from those in fish meal.

Experimental procedures

For this experiment, an enhanced torula yeast produced by Arbiom Inc. (Durham, NC) and a commercial source of fish meal were used (Table 1).

Thirty-two weanling barrows (initial BW: 11.9 ± 1.1 kg) were placed in individual metabolism crates and allotted to a randomized complete block design with 4 diets and 8 replicate pigs per diet. Four cornstarch-based diets were formulated based on enhanced torula yeast or fish meal. Each ingredient was used in 2 diets containing either 0 or 500 FTU of microbial phytase. Feces were collected according to standard procedures using the marker to marker approach with 5-d adaptation and 4-d collection periods. Fecal, ingredient, and diet samples were analyzed for P to calculate digestibility values of P in each ingredient.

Results

Values for ATTD and STTD of P in enhanced torula yeast were greater (P < 0.05) than values for fish meal (Table 2). Pigs fed diets containing enhanced torula yeast had greater (P < 0.05) feed intake than pigs fed diets containing fish meal. In contrast, fecal output, percentage of P in feces, and therefore, P output in feces was less (P < 0.05) from pigs fed diets containing enhanced torula yeast compared with pigs fed diets containing fish meal. However, there was no effect of phytase inclusion on any of the response variables and no interaction between ingredient and phytase was observed.

Key points

  • The ATTD and STTD of P in enhanced torula yeast is greater than in fish meal.
  • There is no effect of inclusion of phytase in the diets on the digestibility of P in the two ingredients.
  • The enhanced torula yeast can be included in diets for weanling pigs at the expense of fish meal.

Table 1. Analyzed composition of ingredients (as-fed basis)

 

Ingredient

Item, %

Enhanced torula yeast

Fish meal

DM

95.17

91.10

Ash

6.40

11.75

Ca

0.22

5.26

P

1.89

3.33

Phytate

0.25

0.82

Phytate-bound P1

Non – phytate P2

0.07

1.74

0.23

3.10

Non-phytate P2

1.74

3.10

1Calculated as 28.2% of phytate.

2Calculated as the difference between phytate P and total P.

 

Table 2. Apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in enhanced torula yeast and fish meal1

Phytase

0 FTU

500 FTU

 

P-value

Ingredient

Enhanced torula yeast

Fish meal

Enhanced torula yeast

Fish meal

SEM

Ingredient

Phytase

Ingredient × phytase

Feed intake, g/d

625.26

529.51

584.99

507.83

33.85

   0.016

0.368

0.786

P intake, g/d

4.26

5.01

4.51

4.71

0.28

   0.102

0.917

0.331

Fecal output, g/d

21.68

34.82

18.94

28.41

3.08

   0.001

0.149

0.557

P in feces, %

2.22

4.97

2.24

5.11

0.24

< 0.001

0.741

0.792

P output in feces, g/d

0.48

1.76

0.42

1.50

0.18

< 0.001

0.384

0.602

ATTD of P, %

88.63

66.20

90.73

68.80

2.58

< 0.001

0.372

0.924

EPL2, mg/d

 

 

STTD of P3, %

110.97

91.23

91.82

68.03

103.56

93.02

87.77

70.66

5.94

2.58

    0.007

< 0.001

0.342

0.400

0.779

0.873

, %

91.23

68.03

93.02

70.66

2.58

< 0.001

0.400

0.

    1Data are least square means of 8 observations.

 2EPL= endogenous P loss; calculated by multiplying the EPL (0.190 g/kg DMI) by the daily DM intake.

 3Values for STTD were calculated by correcting ATTD values by the basal endogenous loss of P.

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