Excretion of phosphorus

Based on calculations using the digestibility equation from the pig data set, P excretion can be reduced by 33.2% when 500 U phytase kg-1 is added to a low P diet, compared with a positive control diet (0.481% P) containing 0.1% units more P (Table 10.3). When the P retention equation from the poultry data set was used to make similar estimates, P excretion was reduced by 31.9% when 500 U phytase kg-1

is added to a low P diet, compared with a positive control diet (0.57% dietary P) which would be 0.1% units higher in P (Table 10.4). Simply lowering the level of dietary P by 0.1% will decrease P excretion by about 8.3% in pigs and 18.4% in poultry. Unless very high levels of P (well above the minimum requirement of the

Table 10.3. Predicted P digestibility, P digested, and percentage reduction in P excretion based on data generated from the pig data set in this study.

Supplemental phytase (U kg-1)

Total P digestibility3 (%)

P digestibilityb by phytase

(%)

P digested by phytasec (%)

Total P excretedd (%)

Decreased P excretione (%)

0

27.9

0

0

0.275

8.3

100

34.2

6.2

0.024

0.251

16.3

200

38.9

11.0

0.042

0.233

22.3

250

40.9

13.0

0.049

0.225

24.8

300

42.6

14.7

0.056

0.219

27.0

350

44.1

16.2

0.062

0.213

28.9

400

45.5

17.5

0.067

0.208

30.6

450

46.6

18.7

0.071

0.203

32.1

500

47.6

19.7

0.075

0.200

33.2

550

48.5

20.6

0.078

0.196

34.5

600

49.3

21.4

0.081

0.193

35.5

650

50.0

22.1

0.084

0.191

36.4

700

50.6

22.7

0.086

0.188

37.1

750

51.1

23.2

0.088

0.186

37.8

800

51.6

23.6

0.090

0.184

38.4

900

52.3

24.4

0.093

0.182

39.4

1000

52.9

25.0

0.095

0.179

40.1

1100

53.4

25.4

0.097

0.178

40.7

1200

53.7

25.8

0.098

0.176

41.1

1300

54.0

26.0

0.099

0.175

41.5

1400

54.2

26.2

0.100

0.175

41.7

1500

54.3

26.4

0.101

0.174

41.9

aGenerated from the equation given in Fig. 10.2 [54.86(1 - 0.4908e-000263A)].

bCalculated by subtracting P digestibility of basal diet without phytase from coefficients at each phytase level.

cCalculated by multiplying the P digestibility due to phytase by the average P content (0.381% total P) of the basal diet. The equation of this data is = 0.1026(1 - e-000263X), where X= phytase level. dCalculated by subtracting total P digestibility coefficients from 100 and multiplying the product by the average P content (0.381% total P) of the basal diet.

eBased on an inorganic P digested equation (Y= -0.167 + 0.755X, r2 = 0.24, where X= % P from inorganic source); 0.0245% P was excreted for the 0.1% unit of added inorganic P above the basal diet making the total P excreted by the positive control diet (0.481% total P) equal to 0.2995% P (0.275 + 0.0245). Decreased P excretion was calculated by subtracting the total P excreted by the phytase supplemented diets from the P excreted by the positive control diet (0.2995%) and then dividing by the P excreted by positive control diet and multiplying by 100. For example, at 500 U phytase kg-1, 33.2% = [(0.2995 - 0.200)/(0.2995)]*100.

pig) are fed, the amount of P excreted in pig urine will generally be minimal and was not considered in the calculations in this chapter; this is consistent with conclusions reached by Jongbloed (1987).

Table 10.4. Predicted P digestibility, P digested, and percentage reduction in P excretion based on data generated from the poultry data set in this study.

Supplemental Total P P digestibility5 P digested Total P Decreased P phytase digestibility3 by phytase byphytasec excretedd excretione

Table 10.4. Predicted P digestibility, P digested, and percentage reduction in P excretion based on data generated from the poultry data set in this study.

(U kg-1)

(%)

(%)

(%)

(%)

(%)

0

52.1

0

0

0.229

18.4

100

54.1

2.0

0.010

0.219

21.8

200

55.9

3.8

0.018

0.211

24.8

250

56.7

4.6

0.022

0.207

26.2

300

57.4

5.3

0.025

0.203

27.5

350

58.1

6.0

0.029

0.200

28.6

400

58.8

6.7

0.032

0.197

29.7

450

59.4

7.3

0.035

0.194

30.8

500

60.0

7.8

0.037

0.191

31.9

550

60.5

8.4

0.040

0.189

32.7

600

61.0

8.9

0.042

0.186

33.5

650

61.5

9.3

0.045

0.184

34.3

700

61.9

9.8

0.047

0.182

35.0

750

62.3

10.2

0.049

0.180

35.7

800

62.7

10.6

0.050

1.178

36.4

900

63.4

11.2

0.054

0.175

37.6

1000

64.3

11.8

0.057

0.172

38.6

1100

64.7

12.4

0.059

0.170

39.5

1200

65.0

12.8

0.061

0.168

40.3

1300

65.4

13.2

0.063

0.166

41.0

1400

65.7

13.6

0.065

0.164

41.6

1500

66.0

13.9

0.066

0.162

42.1

aGenerated from the equation given in Fig. 10.1 [68.18(1 - 0.2354e-000134X)].

bCalculated by subtracting P digestibility of basal diet without phytase from coefficients at each phytase level.

cCalculated by multiplying the P digestibility due to phytase by the average P content (0.478% total P) of the basal diet. The equation of this data (%) = 0.07672(1 - e-000134X), where X = phytase level. dCalculated by subtracting total P digestibility coefficients from 100 and multiplying the product by the average P content (0.478% total P) of the basal diet.

eBased on an inorganic P digested (retained) equation (Y = -0.000936 + 0.484X, r2 = 0.69, where X= % P from inorganic source); 0.0516% was excreted for 0.1% added inorganic P above the basal diet making the total P excreted by the positive control diet (0.578% total P) equal to 0.2804% P (0.2288 + 0.0516). Decreased P excretion was calculated by subtracting the total P excreted by the phytase supplemented diets from the P excreted by the positive control diet (0.2804%) and then dividing by the P excreted by positive control diet and multiplying by 100. For example, at 500 U phytase kg-1, 31.9% =[(0.2804 - 0.191)/(0.2804)]*100.

0 0

Post a comment