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Study: Zinc’s negative effects on mineral digestibility can be mitigated

Pharmacological levels of zinc — 2,000 to 3,000 milligrams per kilogram — help to prevent post-weaning diarrhea, but are not without drawbacks.

Source: University of Illinois Department of Animal Sciences
Researchers at the University of Illinois have shown that a common strategy for reducing post-weaning diarrhea in pigs may have negative effects on calcium and phosphorus digestibility, and suggested management practices to counteract the effects.

The biological requirement for zinc in growing pigs is approximately 50 milligrams per kilogram body weight. However, pharmacological levels of zinc — 2,000 to 3,000 milligrams per kilogram — are sometimes included in diets fed to pigs after weaning. The high levels of zinc help to prevent post-weaning diarrhea, but are not without drawbacks.

“Zinc competes with calcium for absorption in the small intestine of the pig,” says U of I animal sciences professor Hans H. Stein. “In addition, most phosphorus in plant sources is bound to phytate, and zinc can form complexes with phytate and prevent hydrolysis of the phytate molecule by phytase. Therefore, if zinc is included at pharmacological levels in the diets, it can reduce calcium and phosphorus digestibility.”

Stein led a team of researchers that set out to determine if pharmacological levels of zinc oxide in pig diets affect the ability of microbial phytase to improve calcium and phosphorus digestibility. They fed growing barrows diets containing either 0 or 2,400 milligrams per kilogram zinc in the form of zinc oxide, along with either zero, 1,000 or 3,000 units of phytase (FTU) per kilogram.

Standardized total tract digestibility of calcium was 70% for pigs fed diets containing no zinc oxide and no phytase. Apparent total tract digestibility of phosphorus in the same diets was 61.5%. However, when zinc oxide was included in the diets, those values dropped to 67.2% for STTD of calcium and 55.6% for ATTD of phosphorus.

Adding microbial phytase improved calcium and phosphorus digestibility in all diets. However, the improvement in digestibility was reduced in diets containing zinc oxide. In the diets without zinc oxide, adding 3,000 FTU of phytase increased the STTD of calcium by 16%, but the increase was only 9.7% in the high zinc diets. Adding 3,000 FTU of phytase increased the ATTD of phosphorus by 31% and 21%, respectively, in diets without and with zinc oxide.

Stein offered guidelines for producers based on the new research.

“If pigs need pharmacological levels of zinc, the calcium and phosphorus in the diets may need to be increased by 4% and 9.5%, respectively, for 15 kilogram pigs. Alternatively, diets can be supplemented with microbial phytase to prevent reduced absorption of calcium and phosphorus, but the efficacy of phytase will be reduced.”

The paper, “Effects of zinc oxide and microbial phytase on digestibility of calcium and phosphorus in maize-based diets fed to growing pigs,” was co-authored by Laia Blavi of the University of Illinois, and David Sola-Oriol and José Francisco Perez of the Universitat Autònoma de Barcelona. It was published in a recent issue of the Journal of Animal Science.

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