Espinosa, C. D., D. Velayudhan, Y. Dersjant-Li, and H. H. Stein. 2022. Effect of Increasing Levels of a Novel Consensus Bacterial 6-Phytase Variant on Ileal and Total Tract Digestibility of Nutrients in Diets Fed to Young Pigs. J. Anim. Sci. 100(Suppl.2): 34–35. doi.org/10.1093/jas/skac064.056. Link to Abstr.

The effect of microbial phytase on Ca and P digestibility in diets for pigs and poultry is well established. In poultry, it also appears that the effect of phytase in increasing amino acid (AA) digestibility is consistent, but that is not the case when phytase is added to diets for pigs. However, in many experiments, relatively low levels of phytase was used and it is not known if greater concentrations of phytase will result in a different result. A novel phytase has been recently developed; however, it is also not known if this phytase source can increase digestibility of AA and other nutrients. Therefore, an experiment was conducted to test the hypothesis that inclusion of increasing levels of the novel phytase in diets for growing pigs increases the apparent ileal digestibility (AID) of crude protein (CP) and AA, and the apparent total tract digestibility (ATTD) of gross energy (GE) and minerals.

In plant-based feed ingredients there is a considerable amount of P bound to phytate, limiting the amount of P that is available for utilization, but inclusion of microbial phytase in pig diets increases the digestibility of P. The negatively charged phytate molecule can chelate Ca cations resulting in formation of insoluble Ca-phytate complexes. Degradation of phytate by microbial phytase may prevent formation of these non-digestible complexes, resulting in increased Ca digestibility. It is also possible that use of exogenous phytase reduces endogenous loss of Ca. If indeed the reduced endogenous loss of Ca is a result of degradation of phytate, it is expected that increased doses of dietary phytase will linearly reduce endogenous losses of Ca, but this hypothesis has not been experimentally verified. Therefore, this experiment was conducted to test the hypothesis that increasing dietary phytase reduces basal endogenous loss of Ca and increases digestibility of P in growing pigs.

In most plant feed ingredients, the majority of P is bound to phytate, which reduces digestibility of P in pigs, and therefore, the concentration of digestible P in these ingredients is relatively low. Phytate is negatively charged in the intestinal tract and can bind both endogenous and dietary nutrients, which results in precipitation of non-digestible nutrient-phytate complexes. Therefore, it is possible that the use of exogenous phytase can also increase the digestibility of other nutrients than P. As an example, addition of exogenous phytase to diets also releases Ca from phytate, and thus, increases the digestibility of Ca. However, it has not been conclusively demonstrated that phytase also increases the digestibility of energy-generating nutrients and other minerals in diets fed to pigs and inconsistent results among experiments have been reported. Therefore, the objective of this experiment was to test the hypothesis that increasing phytase dose increases the apparent total tract digestibility (ATTD) of minerals and gross energy (GE) in corn and soybean meal-based diets fed to growing pigs.

Lagos, L. Vanessa, Su A Lee, Mike R. Bedford, and Hans H. Stein. 2021. Reduced concentrations of limestone and monocalcium phosphate in diets without or with microbial phytase did not influence gastric pH, fecal score, or growth performance, but reduced bone ash and serum albumin in weanling pigs. Transl. Anim. Sci. 2021.5:1-10. doi.org/10.1093/tas/txab115.

The limited capacity for weanling pigs to secret HCl in the stomach may be exacerbated by inclusion of ingredients with high acid binding capacity such as limestone and monocalcium phosphate. As a consequence, reducing the amount of these 2 ingredients in diets for weanling pigs may contribute to a stable low pH for proper pepsin activity and increased action of microbial phytase. Inclusion of high doses of phytase that results in increased phytate degradation and increased release of Ca, P, and inositol may also be beneficial to newly weaned pigs. Therefore, an experiment was conducted to test the hypothesis that lowering dietary Ca and P reduces gastric pH and diarrhea of weanling pigs, but microbial phytase may overcome negative effects of low Ca and P on growth performance and bone ash.

Lagos, L. Vanessa, Su A Lee, Mike R. Bedford, and Hans H. Stein. 2021. Formulating diets based on digestible calcium instead of total calcium does not affect growth performance or carcass characteristics, but microbial phytase ameliorates bone resorption caused by low calcium in diets fed to pigs from 11 to 130 kg. Journal of Animal Science, 2021, Vol. 99, No. 3, 1–11. doi:10.1093/jas/skab057.

Rundle, Carly M., Barthold Hillen, Yueming Dersjant-Li, Anne-Marie Debicki-Garnier, Hans H Stein. 2020. The effect of increasing phytase dose to 1000 FTU/kg on phosphorous and calcium digestibility in pigs fed diets without inorganic P. J. Anim. Sci. 98(Suppl. 4): 100-101. doi.org/10.1093/jas/skaa278.184. (Abstr.). Link to abstract.

Several experiments were conducted to estimate Ca digestibility in different feed ingredients in the presence or absence of microbial phytase to allow formulation of diets for pigs to be based on standardized total tract digestible (STTD) Ca instead of total Ca. Thus, 4 experiments aimed at determining Ca requirements expressed as a ratio between STTD Ca and STTD P in pigs from 11 to 130 kg. A follow-up study was later conducted to validate those data and to evaluate the effect of using ratios that maximize growth performance on bone development because maximum bone ash requires more Ca than maximum growth performance. However, data indicate that STTD Ca to STTD P ratios to maximize Ca retention are greater than to maximize bone ash synthesis. The use of STTD Ca to STTD P ratios in diet formulation may result in a reduction in excess dietary Ca, which is beneficial because excess dietary Ca is detrimental to P digestibility and growth performance of pigs. Therefore, the objective of this experiment was to test the hypothesis that formulating diets for growing pigs based on a ratio between STTD Ca and STTD P instead of total Ca and STTD P does not decrease Ca retention, but increases P utilization.