Vitamin D regulates a wide spectrum of genes responsible for Ca and P homeostasis and cell differentiation. Cholecalciferol, commonly known as vitamin D₃, is a primary source of vitamin D₃ in diets for growing pigs; however, it needs to be hydroxylated twice to be active. The first hydroxylation occurs in the liver at the 25-position, resulting in 25-hydroxycholecalciferol [25(OH)D₃], whereas the second hydroxylation occurs in the kidneys at the 1-position, resulting in 1,25 dihydroxycholecalciferol [1,25(OH)₂D₃], which is the active form of vitamin D₃ in the body. Supplementation of 25(OH)D₃ to diets for sows in late gestation may increase the apparent total tract digestibility (ATTD) and retention of Ca and P, but there are no data to demonstrate this effect in growing pigs.

Cereal grains commonly used in diets for pigs have low digestibility of P because P is bound to phytate. Exogenous phytase increases the digestibility of both Ca and P in pigs by releasing the P from the phytate molecule within the gastrointestinal tract of pigs. However, there is limited information about the interaction between 25(OH)D₃ and supplemental phytase in diets fed to growing pigs. Therefore, the objective of this experiment was to test the hypothesis that both 25(OH)D₃ and microbial phytase independently and in combination may increase standardized total tract digestibility (STTD) of Ca and P by growing pigs.

Nelson, Megan E., Su A Lee, Carrie Walk, Hans H. Stein. 2024. Effects of source of calcium carbonate and microbial phytase on standardized total tract digestibility of calcium by growing pigs. J. Anim. Sci Vol. 102, Suppl. S2. P 158 - 159. doi.org/10.1093/jas/skae102.175 Link to abstract.

Manaig, Y. J. Y., and H. H. Stein. 2024. Practical feeding: Formulating swine diets to meet Ca and P requirement. Feed Strategy, May-June edition. Page 30-32. Link to full text.

Lopez, Diego A., Su A. Lee, Hans H. Stein. 2022. Effects of microbial phytase on standardized total tract digestibility of phosphorus in feed phosphates fed to growing pigs. J. Anim. Sci. Vol 100, Issue 12, skac350, doi.org/10.1093/jas/skac350. Link to full text.

Stein, Hans H. 2023. Optimun ratios between digestible Ca and digestible P and impact of phytase on growth performance of weanling and growing pigs. XXXVIII Curso de especializacion FEDNA. Pag 213 - 223. Link to full text.

Lagos, Liz Vanessa, Mike Richard Bedford, and Hans Henrik Stein. 2023. Amino acid and mineral digestibility, bone ash, and plasma inositol is increased by including microbial phytase in diets for growing pigs. Journal of Animal Science and Biotechnology 14:152. doi.org/10.1186/s40104-023-00953-x.

It is important that the digestibility of Ca in Ca sources is known to formulate diets based on values for digestible Ca rather than total Ca. Only a small amount of the Ca required by pigs is provided by plant-based ingredients and supplementation of Ca from Ca phosphates and Ca carbonate, is usually required to meet the requirement by pigs. In addition, use of microbial phytase increases Ca digestibility in Ca carbonate, which is one of the major sources of Ca in pig diets.

Differences in Ca digestibility in 4 sources of Ca carbonate produced in the United States have been observed, but it is unknown if there are differences in the ATTD of Ca in calcium carbonate sources produced outside the United States. Therefore, the objective of this experiment was to test the hypothesis that there are differences in the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of Ca and in the response to microbial phytase among 20 sources of Ca carbonate obtained from different parts of the world.

New sources of high protein corn co-products have been recently developed and may be included in diets fed to pigs. Phytase is often employed during fermentation in the bioethanol process to improve the efficiency of fermentation. However, the use of phytase during fermentation may impact the nature of phosphorus (P) in any post fermentation products, which could subsequently alter the levels of phytate-bound and non-phytate P. As a consequence, this may influence digestibility and concentration of digestible P in any feed product derived from fermentation. Therefore, an experiment was conducted to determine the standardized total tract digestibility (STTD) of P in high protein corn fermented products and in the residual distillers dried grains and solubles (DDGS) produced from a fermentation with or without the use of phytase. It is also the objective of this experiment to test the hypothesis that inclusion of phytase during the fermentation process increases P digestibility in corn co-products.

The majority of P in most plant feed ingredients is bound to phytate. Pigs, however, do not synthesize adequate endogenous phytate to release the P bound to phytate, which results in low digestibility of P in field peas. Values for ATTD and STTD of P in field peas without and with phytase have been reported, but there are no comparative values for the ATTD and STTD of P in field peas adding different levels of phytase. The objective of this experiment is to determine the effect of increasing levels of phytase on the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in field peas fed to growing pigs.