An epidemiological assessment of whether the use of high concentrations of zinc oxide in nursery pig diets is associated with post-weaning anemia

Newly weaned pigs require 50-100 mg/kg of zinc in feed to meet dietary requirements (National Research Council). The addition of high levels of zinc oxide (> 2000 mg/kg) in nursery diets is often used as a preventive measure for Escherichia coli diarrhea and to improve growth performance. The mechanism y which this occurs is still not fully understood, however, it is proposed that zinc oxide has an effect on the gastrointestinal microbiome, due to its bacteriostatic effects. Iron and zinc have similar physical and chemical properties and may rely on the same mechanism for absorption from the gut. An imbalance in the concentration of one mineral can have an antagonistic effect on other minerals. Therefore, the objective of this study is to determine whether high levels of zinc oxide in nursery diets is associated with the presence of anemia 3-weeks post-weaning.

Pigs on 20 Ontario (CAN) farms were sampled. Each producer completed a survey answering questions regarding the concentration of zinc oxide in their post-weaning diets and feed tags were collected from these diets to confirm the level of zinc oxide. Each farms was visited twice. The initial visit occurred 1-2 days prior to weaning. Approximately 20 litters per farm were sampled with one small, medium, and large sized piglet selected from each litter (n=1095). An individual body weight and blood sample were taken on the initial visit and then repeated 3 weeks later when the piglets were in the nursery. Hemoglobin was measured using a STAT-Site® M^Hgb handheld meter. A mixed logistic regression model was built, with farm modeled as a random effect, and anemia as outcome. Nursery pigs were defined as anemic if their hemoglobin concentration was ≤90 g/L. Hemoglobin status at weaning, the type of iron administered (iron dextran or gleptoferron), and age at weaning were modeled as fixed effects. Zinc oxide concentration in the feed was categorized: nutritional dose (≤500 mg/kg), high dose (2000-3000 mg/kg), and very high dose (> 3000 mg/kg).

Zinc oxide concentrations in nursery diets ranged from 250-7000 mg/kg. This study found the odds of anemia was 3.4 and 4.1 times greater for pigs consuming high and very high concentrations of zinc oxide, respectively, compared to those consuming diets containing ≤500 mg/kg of zinc oxide (P< .05).

This study found that high feed levels of zinc oxide (> 2000 mg/kg) were associated with a higher odds of anemia in pigs 3-weeks postweaning. Further research is needed to determine how to off-set the risk of anemia when using zinc oxide to prevent post-weaning diarrhea. Funding: Ontario Pork, the University of Guelph-OMAFRA Research Partnership and Swine Innovation Porc.

Disclosure of Interest: None Declared.