Feed & Additive Magazine Issue 4 May 2021

SPECIAL STORY FEED & ADDITIVE MAGAZINE May 2021 39 many other countries in Asia (e.g Korea) and Amer- icas (e.g: Canada). WHY BANNING PHARMACOLOGICAL ZNO? 1. Zinc and microbial resistance Intensive usage of zinc in animal diets favours the development of bacterial resistance. Bacteria regulate intracellular zinc concentration with a system of ef- flux pumps. These pumps can be specific to zinc or can evacuate other molecules like antibiotics. High levels of zinc tend to increase their synthesis; thus, the use of zinc oxide at pharmacological dosages re- duces the sensitivity of bacteria to antibiotics. 2. Negative nutritional interactions Studies about interactions between zinc and phy- tase suggest that pharmacological dosages of zinc have a negative effect on phytase activity and con- sequently on phytate-phosphorus liberation. This implies a reduced efficacy in phytase functions and possible phosphorus deficiency for affected animals. The acid binding capacity of zinc oxide is the greatest among feedstuffs. Thus, high levels of zinc oxide appear to be antagonistic with feed acidifiers, like organic acids. Moreover, high levels of zinc results in overproduc- tion of metallothionein. This intestinal transporter binds preferentially to copper and consequently may lead to a sub-deficiency of this trace mineral. 3. Environmental concerns Using 3 kg ZnO / ton of feed during the first two weeks after weaning increases by almost 30% the to- tal quantity of zinc excreted in the pig’s growing life. Technological treatments of pig slurry accentuate the problem as they concentrate the zinc in the solid fraction, and the level in the by-product may then exceed the maximal zinc level authorized for organic fertilizers in the EU. 4. Contamination by heavy metals Impurities in commercial zinc oxide are a real problem when zinc quality is not strictly con- trolled. A study from the French institute IFIP indicated that cadmium concentration in kidneys exceeds the regulatory limit (1 mg/kg) for human consumption when pigs are fed with contaminat- ed diets (0.5 mg Cd/kg diet) between 42 and 160 days. Cadmium is known for its organ toxicity and long elimination period; consequently, if tissues are contaminated during the post-weaning period