The influence of calcium on phytase efficacy in non-ruminant animals

High dietary calcium (Ca) can negatively influence growth performance and reduce phosphorus, protein and amino acid digestibility in broilers and pigs. In addition, high dietary Ca will precipitate with phytate at pH conditions within the small intestine. Previous research reported that high dietary Ca significantly reduced phytase efficacy through precipitation with or competition for binding sites on the phytate molecule. However, microbial phytases are active at pH ranges where phytate is soluble and hydrolyse phytate rapidly to reduce the likelihood of phytate precipitating with Ca, suggesting the effect of dietary Ca on the efficacy of these phytases may be reduced. Even with such phytases there may still be problems observed due to particularly high concentrations of dietary Ca, which can occur as a result of a reduction in Ca not being applied in the presence of a phytase and/or if Ca concentrations in the diet exceed expectations. For example, when total Ca was analysed in 795 broiler and pig diets, on average, there was 0.22% more Ca present than expected. This means that if a diet was formulated to contain 0.80% total Ca, the analysed value could be as high as 1.02%, almost 25% above the expected dietary Ca concentration. The discrepancy between the expected and analysed total Ca may have implications on chemical and physical properties within the gastrointestinal tract, dietary phytate solubility, nutrient digestibility and phytase efficacy. The present paper aims to highlight factors influencing the effect of Ca on phytase efficacy, encompassing the differences among published book values for total Ca content of ingredients, the difference between Ca sources and their affinity for phytate, and finally how these factors influence the Ca to P ratio and thus phytase efficacy.