Most of the phosphorus in corn and other plant-based feed ingredients fed to pigs is bound to phytate. Pigs do not secrete phytase in adequate quantities to liberate significant amounts of phytate-bound phosphorus, meaning that most of the phosphorus in these ingredients is not biologically available. Calcium digestibility is also negatively affected by the presence of phytate in feed ingredients. One way for producers to ensure that pigs' requirements are met is to add supplementary phosphorus to diets. However, this adds to the cost of diets. The excretion of phytate-bound phosphorus also may contribute to algae overgrowth in waterways.

Another approach is to add supplemental phytase to the diets, to allow pigs to better utilize the phosphorus present in the ingredients. Phytases can be obtained from plants, animals, or microorganisms (bacteria, yeasts, and fungi).

GraINzyme is a source of phytase produced by genetically modified corn plants with genes derived from E. coli. In this experiment, the effect on growth performance, apparent total tract digestibility (ATTD) of calcium and phosphorus, and bone mineralization of adding GraINzyme to weanling pig diets was tested.

Long, C. J., L. B. Kondratovich, M. F. Westphalen, H. H. Stein, and T. L. Felix. 2017. Effects of exogenous phytase supplementation on phosphorus metabolism and digestibility of beef cattle. Transl. Anim. Sci. 1:168-178. Link to full text (.pdf)

Blavi, L., D. Solà-Oriol, J. F. Pérez, and H. H. Stein. 2017. Effects of zinc oxide and microbial phytase on standardized total tract digestibility of calcium in maize-based diets fed to growing pigs. J. Anim. Sci. 95(Suppl. 5):85 (Abstr.) Link to abstract (.pdf)

Blavi, L., D. Sola-Oriol, J. F. Pérez, and H. H. Stein. 2017. Effects of zinc oxide and microbial phytase on digestibility of calcium and phosphorus in maize-based diets fed to growing pigs. J. Anim. Sci. 95:847-854. Link to full text (.pdf)

Zinc oxide, when added to weanling pig diets in pharmacological quantities of up to 2,500 mg/kg, can help prevent diarrhea during the post-weaning period. However, adding large quantities of zinc to diets has drawbacks. Zinc can interfere with calcium digestibility because it competes for the same transport pathway in cells lining the small intestine. Zinc may also reduce calcium digestibility by forming complexes with calcium and phytate.

The standardized total tract digestibility (STTD) of calcium in various ingredients has only recently been determined, and possible interactions between zinc and phytase on the STTD of calcium have not yet been reported. Therefore, an experiment was conducted to determine the effects of addition of zinc oxide and microbial phytase on STTD of calcium in diets fed to weanling pigs.

She, Y., D. Li, and H. H. Stein. 2016. Effects of microbial phytase on the apparent and standardized total tract digestibility of calcium in milk co-products fed to growing pigs. J. Anim. Sci. 94(E-Suppl. 5):436-437 (Abstr.) Link to abstract (.pdf)

Liu, Y., J. C. González-Vega, M. Vázquez-Añón, J. Zhao, J. Escobar, F. N. Almeida, and H. H. Stein. 2016. Effects of a novel phytase on growth performance and metacarpal bone ash in weanling pigs. J. Anim. Sci. 94(Suppl. 2):111-112 (Abstr.) Link to abstract (.pdf)

Most swine diets must be supplemented with calcium because most plant ingredients commonly used in diets for pigs contain relatively little calcium. One way to add calcium is to include inorganic sources such as dicalcium phosphate or calcium carbonate; however, animal ingredients such as meat byproduct meals can also be used. These ingredients, often used as a protein source, are also a good source of calcium. To our knowledge, values for apparent (ATTD) and standardized (STTD) total tract digestibility of calcium in animal sources have not been reported. Therefore, an experiment was conducted to determine the ATTD and STTD of calcium in four calcium sources of animal origin.

The secondary objective of the study was to test the hypothesis that the addition of microbial phytase to diets containing calcium sources of animal origin would increase the digestibility of calcium. Although animal sources do not contain phytate, swine diets are composed primarily of plant ingredients, and the phytate in those ingredients might form complexes with the calcium in the animal sources.

Soy protein concentrate is produced by extracting some of the non-protein components of soybean meal, including soluble carbohydrates, from soybean meal. These soluble carbohydrates include oligosaccharides, which reduce the tolerance of young pigs to conventional soybean meal. With the oligosaccharides removed, soy protein concentrate can be used as a source of protein in diets for weanling pigs.

Most soy protein concentrate is produced using an alcohol extraction process. However, a new source of soy protein concentrate called Nutrivance (Midwest Ag Enterprises Inc., Marshall, MN) has recently been introduced, which uses a process combining non-alcohol extraction and enzymatic treatment of soybean meal. An experiment was conducted to determine the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus in this new ingredient.