Milk co-products are used in pig diets to provide lactose and, in some cases, high quality protein. In addition, milk co-products also provide calcium to the diets. However, this calcium can potentially bind to the phytate contained in the plant ingredients in the diets, which would reduce its digestibility.
The inclusion of microbial phytase in diets fed to pigs frees calcium that is bound to phytate. An experiment was conducted to determine if the apparent total tract digestibility (ATTD) and the standardized (STTD) total tract digestibility of calcium in milk co-products is improved when microbial phytase is added to the diets.
Experimental design
Sixty-four pigs with an average initial body weight of 15.97 kg were fed one of eight diets. The basal diet contained corn, cornstarch, potato protein isolate, soybean oil, calcium carbonate, and monosodium phosphate. Three diets were formulated by adding whey powder, whey permeate, or skim milk diet to the basal diet at the expense of corn. Four additional diets that were identical to the first four with the exception that 1,000 units (FTU) of microbial phytase were included were also formulated. All diets contained 0.60% total calcium.
Microbial phytase does not increase the digestibility of calcium in milk co-products
Adding microbial phytase to the diets increased (P < 0.05) the ATTD and the STTD of calcium in the diets (Table 1). There was no interaction between diet and phytase. However, the ATTD and STTD of Ca in the milk co-products did not change when phytase was added to the diets (Table 2). The ATTD and STTD of calcium was not different in whey powder and skim milk powder, and greater (P < 0.05) in those ingredients than in whey permeate. This was the case whether or not microbial phytase was included in the diets.
Because microbial phytase increased the digestibility of calcium in the diets, but not in the milk co-products, it is concluded that calcium from other sources in the diets, such as the plant ingredients and calcium carbonate, was bound to phytate and calcium from the milk co-products was not.
Key points
- Whey powder and skim milk powder have greater ATTD and STTD of calcium than whey permeate if fed to pigs.
- Inclusion of microbial phytase can increase the ATTD and STTD of calcium in diets containing milk co-products. However, the increase is due to improved digestibility of the calcium in other sources such as plant ingredients or calcium supplements, but the digestibility of calcium in the milk co-products is not improved by phytase.
Table 1. Apparent and standardized total tract digestibility (ATTD and STTD) of calcium in diets containing whey powder, whey permeate, or skim milk powder without or with microbial phytase
|
|
No phytase |
With phytase |
|
P-value |
||||||||
|
Item |
Basal |
Whey powder |
Whey permeate |
Skim milk powder |
Basal |
Whey powder |
Whey permeate |
Skim milk powder |
SEM |
Diet |
Phytase |
Diet × phytase |
|
ATTD of Ca, % |
66.6 |
84.3 |
62.2 |
85.6 |
72.7 |
83.0 |
72.2 |
89.6 |
2.6 |
<0.001 |
0.011 |
0.157 |
|
STTD of Ca, % |
68.4 |
86.2 |
64.1 |
87.5 |
74.5 |
84.9 |
74.1 |
91.4 |
2.6 |
<0.001 |
0.011 |
0.158 |
a-dMeans within a row lacking a common superscript letter are different (P< 0.05).
Table 2. Apparent and standardized total tract digestibility of calcium in whey powder, whey permeate, and skim milk powder without or with microbial phytase1
|
Ingredients |
Phytase (FTU/kg) |
P-value |
|||||||
|
Item |
Whey powder |
Whey permeate |
Skim milk powder |
SEM |
0 |
1,000 |
SEM |
Ingredient |
Phytase |
|
ATTD of Ca, % |
96.7a |
60.7b |
95.0a |
5.0 |
89.5 |
78.7 |
5.0 |
<0.001 |
0.143 |
|
STTD of Ca, % |
98.5a |
62.8b |
97.4a |
5.0 |
91.7 |
80.8 |
5.0 |
<0.001 |
0.142 |
1The ingredient × phytase interaction was not significant, and therefore, only main effects are reported.
a-bMeans within a row lacking a common superscript letter are different (P< 0.05).
This report is based on unpublished data by Yue She, Laura Merriman, and Hans H. Stein.