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.