Editor’s note: article published by permission from Dr. Danyel Bueno Dalto, Sherbrooke Research and Development Centre and the Animal Nutrition Association of Canada — ANAC

Despite environmental and public health (bacterial resistance) issues, supranutritional levels of zinc oxide (ZnO) are still commonly used to prevent diarrhea in post-weaning piglets. In Canada, these levels represent more than eight-fold the Canadian Food Inspection Agency (CFIA) proposed maximum levels at 300 mg/kg, said Dr. Danyel Bueno Dalto, Sherbrooke Research and Development Centre.

The limited knowledge of the consequences for the metabolism of trace minerals has hampered the replacement of this strategy without compromising piglet health, he said during the 2023 Animal Nutrition Conference of Canada.

Dalto and colleagues performed a series of studies to better understand the impact of dietary zinc (Zn) levels on trace mineral metabolism. In a bioavailability study, Zn concentrations of 200 mg/kg impaired copper (Cu) intestinal absorption at 20 mg/kg, he said.

In a metabolism study using supplemental Zn at 100, 1000, 3000 mg/kg and Cu at 130 mg/kg, Zn provision at 3000 mg/kg as zinc oxide (ZnO) was inadequately regulated by the organism with the potential induction of Cu and iron (Fe) deficiency under long-term supplementation during the post-weaning period, Dalto explained.

The results of the studies indicate that optimal dietary ratios among these minerals are needed to improve their homeostasis. This was confirmed in another bioavailability study where a Zn/Cu ratio of 15:1, within nutritional levels, optimized the absorption of Zn and Cu, he noted.

In a long-term metabolism study using different dietary Zn/Cu ratios (3000/130, 3000/6, 100/130, 100/6), the risk of Cu deficiency was confirmed, and lower dietary Zn/Cu ratios were shown to optimize Cu without compromising Zn metabolism, Dalto said.

Dalto concludes that dietary ZnO levels play a major role in modulating the metabolism of Zn, Cu and Fe in post-weaning piglets, with potential detrimental health effects.