to phytate increases with limestone solubility. Solubilisation rates, and therefore the digestibility of phosphorous, varies among particle sizes: finer particles dissolve faster in the gut and, thus, have a greater negative impact on phosphorous digestibility. However, this effect is not linear and particle size alone does not explain all the variations in calcium availabil- ity according to limestone source. Other factors, such as the physical and chemical characteristics of the rock, might also play an important role. Therefore, to evaluate the impact of dietary calcium on phosphorous digestibility and properly formulate diets, the total calcium concentration in the diet as well as the limestone solubility need to be considered.
The role of phytase in minimizing the anti-nutritional effects of calcium Phytases are commonly added to monogastric feed formu- las to partially or fully replace the need to add inorganic phosphorous. Phytases also reduce the negative impact of excessive calcium supplementation on the digestibility of amino acids and phosphorous. This ability depends both on phytase-related factors, such as its specific pH range of action and supplementation dose, as well as on dietary-related factors, including dietary calcium levels and calcium-phos- phorous ratios. As calcium binds phytate more easily with increasing pH, phytase has limited time to act upon phytate and release phosphorous before phytate becomes unavaila- ble. A fast-acting phytase with a superior pH profile can there- fore increase phytate hydrolysis in the gut, quickly releasing phosphorous for absorption and reducing the formation of insoluble calcium-phytate complexes. Axtra PHY GOLD, a con- sensus bacterial 6-phytase variant, is highly active at low pH (2.5−4.0). It breaks down phytate quickly in the gizzard and proventriculus, hydrolysing it before entering the small intes- tine, which results in less insoluble calcium-phytate complex- es. Compared to competitor phytases, this phytase showed greater ability to hydrolyse phytate in the presence of calcium, thus reducing the negative impact of this mineral (Figure 1).
Calcium-rich diets, such as starter diets of young animals, re- quire specific phytase supplementation. When evaluated in both low and highly soluble calcium conditions in piglets (Figure 2), Axtra PHY GOLD supplementation at 1000 FTU/kg mitigated the negative impact of low soluble calcium on di- gestive performance. Higher doses of the enzyme (2000 FTU/ kg) overcame the negative impact of highly soluble calcium.
Customised solution for calcium Ensuring the best performance outcomes of calcium-rich diets requires understanding the characteristics of both the raw materials and the enzymes present in feed formulations. Calcium sources vary in particle size, solubility, and mineral content, which are unique features of each limestone. The anti-nutritional effects of calcium supplementation will, therefore, depend on the calcium source and on the quality of the selected phytase. As calcium anti-nutritional effects are unveiled, customized supplementation of both calcium source and phytase emerge as the key concept for maximising animal growth performance.
Figure 2 - Axtra PHY GOLD effects on the digestive phosphorous (P) at low and highly soluble calcium (Ca) conditions in the gut of piglets.
PC NC
Axtra® PHY GOLD 1000 FTU/kg Dig P, g/kg
2.54a 2.05ab 2.20ab 1.92abc 1.72abc 1.52bcd 0.98cd 0.72d Axtra® PHY GOLD 2000 FTU/kg
At 2000 FTU/kg, the enzyme overcame the negative impact of highly soluble Ca on the diges- tive perfor- mance of pig- lets.
Low Soluble Ca
High Soluble Ca ▶ ALL ABOUT FEED | Volume 29, No. 7, 2021 31
PHOTO: JAN SIBON FOTOGRAFIE
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