Phosphorus (P) is an essential and expensive mineral for pigs, crucial for bone development, energy metabolism, and various physiological processes. The phosphorus requirement for pigs is dependent upon:
(1) An adequate supply of P in an available form,
(2) A suitable ratio of available Ca and P in the diet, and
(3) The presence of adequate vitamin D.
Phosphorus in protein sources of animal origin is largely inorganic and has a high relative bioavailability (RBV). However, the RBV of P in meat and bone meal (MBM) is variable (67-90%). Phosphorus in inorganic supplements also varies in RBV (Table 1, Jondrevvill and Dourmad, 2006). The RBV of MCP and MDCP is strongly affected by citric acids solubility and ammonium citrate solubility, respectively. Usually, the water solubility for MCP and MDCP is required to be greater than 80% and 50%, respectively.
Table 1. RBV and the digestibility coefficient of different inorganic P sources
In cereal grains and oil seed meals, about 60-75% of P is organically bound in in the form of phytate. The exogenous phytase supplementation can result in major improvement in RBV of phytate P. The higher temperature during pelleting of diets can reduce or destroy phytase activity and thermal stable phytase is available now to resist up to 85 ˚C pelleting temperature (Table 2).
Table 2. VTR phytase activity and heat stability (North Carolina State University)
To limit the loss of activity, Phytase must be made resistant to digestive proteases. After 2 h in contact with pepsin, VTR phytase retained about 93% of their initial activity (Figure 1).
Figure 1. The effect of pepsin on phytase activity.
A wide Ca-to-P ratio lowers P absorption and resulted in reduced growth and bone calcification. Ca and P requirements for maximizing bone strength are at least 0.1 percentage units higher than that maximal body weight gain. Although every 1-gram phytate P released by phytase could spare 1.33 grams Ca availability, a suggested ratio of total Ca to total P is between 1:1 and 1.25. It is noticed that the Ca in calcitic limestone is highly available, but Ca in dolomitic limestone is only 50 to 75% available.
An adequate vitamin D is necessary for proper metabolism of Ca and P, but a very high level of vitamin D can mobilize excessive amounts of Ca and P from bones.
A study compiled by our Redox Animal Nutritionists.