Effect of Ca Levels on Performance, Bone Ash and Ileal Digestibility of Ca and P in Broilers

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Article | 18.09.2021
A practical example of the role calcium (Ca) has on phosphorus (P) digestibility was demonstrated in a recent broiler trial at the University of Warmia and Mazury, Poland.

Feed was reformulated with 1,000 FTU/kg of OptiPhos® Plus 5000 G while 1,500 EPU/kg of Hostazym® X 15000 was added on top.

The three different Ca treatments were:

  • Normal Ca level: 8.5, 7.0 and 6.0 g Ca/kg feed in the starter, grower and finisher diet, respectively
  • Reduced Ca level: 7.0, 6.0 and 5.0 g Ca/kg feed in the starter, grower and finisher diet, respectively
  • Low Ca level: 6.5, 5.0 and 4.0 g Ca/kg feed in the starter, grower and finisher diet, respectively

The overall technical performance of the birds was very good (the European Production Efficiency Factor (EPEF) was > 500) showing the potential of using a double dose of OptiPhos® Plus combined with Hostazym® X on top to enhance broiler performance.

The following effects of Ca on performance were noted (Figure 1): 

  • Reducing the Ca level led to increased growth with the lowest Ca level giving a significantly higher end weight compared to diets containing normal Ca levels (p < 0.05) 
  • Feed conversion was not impacted despite the higher end weights at reduced and low Ca levels
Figure 1. Effect of lowering Ca levels on body weight and feed conversion at dat 35. Values with a different superscript (a,b) are significantly different at p < 0.05


The effect of reducing Ca on the Ca and P digestibility (at day 35), and bone ash analysis (at day 21; Table 1) showed that:

  • Ca digestibility was highest at the lowest Ca inclusion level
  • P digestibility was also highest at the lowest Ca inclusion level
  • The improved digestibility of P as a result of reducing the Ca level gave OptiPhos® Plus at 1,000 FTU/kg an extra matrix value of 0.3 g available P/kg feed
  • Tibia ash, and Ca and P levels in tibia ash, decreased as the amount of Ca decreased

The fact that low Ca levels optimized technical performance, but tended to reduce bone ash, demonstrates that the Ca requirement for optimal bone growth is higher than the Ca requirement for optimal performance.

Table 1. Ileal digestibility of Ca and P, tibia ash content, and Ca and P content in tibia ash



  • Reducing the Ca level had a significant positive impact, not only on animal performance, but also on Ca and P digestibility and thereby on the efficiency of OptiPhos® Plus, yielding higher P matrix values.
  • Reducing Ca levels might impact bone formation slightly, showing that Ca requirements for bone formation might be higher than the Ca requirement for optimal animal performance.
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