Zinc overload in weaned pigs: tissue accumulation, pathology, and growth impacts

Abstract

Zinc oxide (ZnO) is commonly fed to pigs at pharmacologic concentrations (2,000–3,000 ppm) for the first 3 wk post-weaning to increase growth and reduce enteric bacterial disease. The safety of this high-dose treatment is assumed based upon lower bioavailability of ZnO compared to other common forms of Zn in feed; however, limited data are available regarding the specific serum and tissue concentrations of Zn expected in animals experiencing overload following feeding of excessive ZnO. Fifty-five 3-wk-old pigs were divided into 5 groups receiving various concentrations of ZnO (0–6,000 ppm) for 3 wk. Pigs receiving 6,000 ppm ZnO had higher mean pancreatic Zn concentrations ( p < 0.001) compared to other treatments, and higher pancreatic Zn concentrations were associated with pancreatic acinar cell apoptosis ( p < 0.0001). Hepatic Zn concentrations were highest for pigs receiving 6,000 ppm ZnO (mean ± SEM; 729 ± 264 ppm) and significantly higher than all other groups ( p < 0.0001), with controls having concentrations <60 ppm. Similarly, serum Zn was highest in pigs receiving 6,000 ppm ZnO (4.81 ± 2.31 ppm) and significantly higher than all groups (controls, <1 ppm). Additionally, as pigs became overloaded with Zn, there were significant reductions in serum Cu and both serum and hepatic Se. Hepatic and serum Zn concentrations >500 ppm and >2 ppm, respectively, are indicative of Zn overload, and dietary trace mineral analysis is warranted if expected inclusion rates are ≤3,000 ppm ZnO.

Chronic pancreatitis in farmed pigs fed excessive zinc oxide

“…17 Similarly, there was no significant difference in body weight between treated and control pigs. 1,4 However, the exposure periods were shorter and the ZnO concentrations were lower than in our study.…”

“…4 It has been reported that high doses of ZnO (4,000–6,000 ppm, 3 wk) induce pancreatic acinar cell apoptosis. 1 Nevertheless, we found no reports of Zn poisoning in farm-reared pigs; histologic and immunohistochemical examinations of their organs and tissues are lacking.…”

“…Earlier studies on Zn poisoning reported no change in the size, shape, or distribution of islet cells after short-term (3 wk) Zn exposure in piglets. 1,4 However, no prior study has reported the effects of long-term, high-dose ZnO (8,000 ppm; >4 mo). Pancreatic islet β cells use Zn for insulin synthesis, storage, and secretion.…”

Towards Zero Zinc Oxide: Feeding Strategies to Manage Post-Weaning Diarrhea in Piglets

“…The large and prolonged employment of ZnO at pharmacological levels in pig farming has raised several concerns, as depicted in Figure 2. Too high or too much protracted ZnO supplementations lead to the loss of ZnO benefits with the potential onset of toxic effects [22,61,62], because of the excessive accumulation of Zn in animal tissues such as kidney, liver, and pancreas [63,64], which can experience Zn overload [62].…”

Recent Advances in Understanding the Influence of Zinc, Copper, and Manganese on the Gastrointestinal Environment of Pigs and Poultry

“…In addition, the form of the trace mineral (e.g., inorganic vs. organically-complexed) can influence these interactions and its bioavailability [ 2 ]. Moreover, feeding supra-nutritional or pharmacological levels of a trace mineral could lead to mineral imbalances and deficiencies [ 7 ].…”