Swine Management Resources - PIC


Macro minerals are involved in many processes ranging from structural framework of DNA and RNA to bone development, electrolyte balance, and growth performance. Thus, fine tuning the macro minerals levels in diet formulation is a key aspect of a well-formulated diet.

Macro minerals such as calcium (Ca) and phosphorus (P) are mainly involved in structural functions such as bone development and metabolism but also are involved in other metabolic functions. Typically, the minimum P levels of the diet are defined, and then the Ca level is defined as a ratio to P. It is generally recommended that the total Ca to total P ratio be between 1 to 1.5. The NRC (2012) concluded that a wider ratio lowers P absorption, especially if P is marginal in the diet.


  • Total phosphorus: Total P represents all P that the ingredient contains (including the non-available P);
  • Bioavailable phosphorus
    • Available phosphorus is estimated by using a method called “slope-ratio assay” and estimates the digestible plus post-absorptive utilization of P at the tissue level; however, this method is more expensive and assumes that an inorganic standard is 100% available.
    • Digestible phosphorus
      • Apparent Total Tract Digestible (ATTD) P: estimates the total tract digestibility of P and does not correct for basal endogenous P losses;
      • Standardized Total Tract Digestible (STTD) P: estimates the total tract digestibility of P and corrects for basal endogenous P losses;

The STTD P way of expressing phosphorus is becoming more common among researchers and nutritionists around the world. This manual provides requirements in an available P and STTD P basis.

Calcium has been mainly expressed in a total basis until this point. Recent work has been focusing on defining digestible calcium levels from different feed ingredients and this may be used in diet formulation in the years to follow. However, at this point, this manual will focus on total calcium. Another consideration with calcium is that some ingredients and feed additives may contain calcium sources as densifiers or diluents. Many times these sources are not accounted for in diet formulation and may have significant impact on the Ca to P ratio.

Sodium is important for maintaining homeostasis of water and electrolytes and can be easily supplemented by adding salt to the diets. Inadequate water supply can induce “salt poisoning”. Sodium deficiency can reduce feed intake, average daily gain, and worsen feed efficiency. Fraser et al. (1987) have reported that salt deficiency can induce tail biting. Finally, it is important to monitor sodium levels in feed ingredients to ensure that the expected formulated levels are achieved.

Swine Management Resources - PIC