## 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

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.

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