FEATURE
Nutritional values of different feed phosphates in shrimp trials
I
by J Zwart, Technical Manager Feed Ingredients, Aliphos, Belgium
t is a common trend nowadays to replace more and more fish meal by vegetal protein sources when formulating shrimp feeds. However, phosphorus (P) levels in these vegetal protein sources are low and above all the greater part of the phosphorus is present in the form of phytate. Phytate degradation is slow in practical shrimp diets resulting in a low P-digestibility. Thus, addition of inorganic phosphates to shrimp feeds is nowadays needed to fulfill the shrimp phosphorus requirements. Phosphorus is important in a large number of biological processes. Some examples are: necessary for building the exo-skeleton, key element in energy metabolism (ATP – ADP), acid-base buffering in blood, component of tissue cell walls. An adequate supply is, therefore, a necessity. Not reaching adequate levels of phosphorus will have repercussions in view of reduced performance, increased deformities, excessive mortality, etc. Dietary supplementation of phosphorus above the requirement results in high P-excretion in the surrounding water contributing to environmental pollution eventually resulting in algae bloom and eutrophication of the water reserves. It is, therefore, of the utmost importance to evaluate the digestibility and retention of inorganic P-sources to meet the P-requirements of the shrimp but to avoid excessive supply and phosphorus excretion. Also, there is still little knowledge on the mineral requirements as well the availability/digestibility of minerals in case of shrimp. Therefore, Aliphos commissioned a trial to Wageningen University, The Netherlands, in which the phosphorus digestibility and retention of different inorganic feed phosphates was measured with white leg shrimp, Litopenaeus vannamei. In this trial three widely used inorganic feed phosphates were tested, dicalcium phosphate (DCP1), monocalcium phosphate (MCP2) and Aquaphos (MAP3).
Table 1: Composition of the diet composition
NC
DCP
MCP
Aquaphos
DM, % Crude protein, % Crude fat,% Total P, % Ca, % Energy, KJ/ g DM
91.3 43.8 6.1 5.9 3.8 20.7
91.2 44.0 6.2 10.0 9.8 20.6
90.6 44.0 6.3 9.9 9.8 20.6
91.2 45.1 5.9 9.9 3.6 20.7
Table 2: Performance results
Contr.
Aquaphos
DCP
MCP
Growth period, d
35
35
35
35
No. of tanks
4
4
4
4
No. of shrimp / tank
27
27
27.5
27
Survival, %
88.9
90.7
89.9
88.0
Body weight start, g
3.73
3.73
3.73
3.67
Body weight end, g
13.0
13.6
12.9
13.1
Growth, g/d
0.27
0.28
0.26
0.27
SGR, %/d
3.58
3.70
3.55
3.64
Feed intake, g/d
0.26
0.25
0.26
0.27
FCR (g/g)
0.97ab
0.90a
0.99b
0.98b
Table 3: Body composition shrimp
Initial
Con
AquaPhos
DCP
MCP
Dry matter, g/kg
213.6
242
232
238
240
Ash, g/kg fresh
33
29
30
29
29
Protein, g/kg fresh
170
189
183
185
187
Phosphorous, g/kg fresh
2.8
2.28a
2.61bc
2.26a
2.44ac
Calcium, g/kg fresh
7.9
5.97
6.14
5.99
5.72
Materials and methods
A trial feed – control- was formulated composed out of ingredients with a low phosphorus and phytate content. Total P-content of the control 5.9g, to this the different feed phosphates were added to arrive on a level of 10g P. Diets were isonitrogenous (crude protein, 44% DM), isolipidic (6.2% DM) and isoenergetic (gross energy, 20.5KJ/g DM) (Table 1). Yttrium oxide was added as an inert marker to enable calculation of
Figure 1: P-retention tested feed phosphates
22 | August 2018 - International Aquafeed