Environmental responsibilities of livestock feeding using trace mineral supplements

Abstract

Trace elements are essential dietary components for livestock species. However, they also exhibit a strong toxic potential. Therefore, their fluxes through the animal organism are tightly regulated by a complex molecular machinery that controls the rate of absorption from the gut lumen as well as the amount of excretion via faeces, urine and products (e.g., milk) in order to maintain an internal equilibrium. When supplemented in doses above the gross requirement trace elements accumulate in urine and faeces and, hence, manure. Thereby, trace element emissions represent a potential threat to the environment. This fact is of particular importance in regard to the widely distributed feeding practice of pharmacological zinc and copper doses for the purpose of performance enhancement. Adverse environmental effects have been described, like impairment of plant production, accumulation in edible animal products and the water supply chain as well as the correlation between increased trace element loads and antimicrobial resistance. In the light of discussions about reducing the allowed upper limits for trace element loads in feed and manure from livestock production in the European Union excessive dosing needs to be critically reconsidered. Moreover, the precision in trace element feeding has to be increased in order to avoid unnecessary supplementation and, thereby, heavy metal emissions from livestock production.

Keywords: Accumulation; Environment; Homeostasis; Livestock; Pharmacological supplementation; Trace element.

Fig. 1

Basic principles of trace element homeostasis in mammal organisms. The organism provides a steady state of trace element contents behind the gut barrier by regulation of absorption and excretion (Windisch, 2002).

Fig. 2

Response of apparently digested feed zinc to varying levels of dietary zinc supply as an example for the response behavior of biomarkers of trace element homeostasis (Brugger et al., 2014). The red line marks the transition point from alimentary zinc deficiency to sufficient feeding at a brutto zinc requirement threshold (X_B) of 58 mg Zn/kg feed.

Fig. 3

Response of faecal zinc and zinc retention to varying zinc intake (Windisch and Kirchgessner, 1995).

Fig. 4

Response of dry tissue (A) zinc and (B) copper content to varying alimentary zinc and copper supply, respectively (Schell and Kornegay, 1996, Fry et al., 2012).

Fig. 5

Relationship between zinc load in pig manure and the percentage abundance of phenotypic antimicrobial resistant Escherichia coli (Hölzel et al., 2012). Values in parentheses represent estimated dry matter zinc contents of manure.