35 Zinc, copper, potassium, sulfur, and iron excretion in pigs.

Abstract Minerals are key components in multiple physiological reactions in pigs. Although mineral requirements are well established, the swine industry often feeds minerals in amounts that exceed these nutritional needs. The excretion of undigested minerals contributes to environmental concerns such as water eutrophication, soil and plant toxicity, and public health risks. This study aimed to develop predictive models for mineral excretion in wean-to-finish pigs using a meta-regression approach. A total of 54 published studies were identified from six databases using specific keywords in the title and abstract and the selection of each study followed PRISMA flowchart guidelines. Extracted data included study characteristics, diet composition, performance criteria, mineral form, and mineral excretion (mg/d). Data for Zn and Cu were categorized into two scenarios: 1) diets meeting or below vs. 2) diets exceeding nutritional requirements, whereas Fe, K, and S were represented only by values exceeding dietary requirements. A backward stepwise selection was applied within each scenario to identify key predictors of mineral excretion, with model selection based on Akaike’s Information Criterion. Selected models include the study as a random effect and were weighed based on the number of repetitions from each study. Although interactions between minerals and mineral form influenced excretion, their contributions were minimal with mineral intake the determining factor affecting excretion. For example, when Zn was fed at or below requirements, P and Fe intake significantly impacted fecal Zn excretion; however, Zn excretion only increased by 1.2 mg/d for every gram that P intake increased and reduced by 0.05 mg/d for every mg that Fe intake increased. For pigs fed Zn over the requirements, Zn form affected Fecal Zn excretion. The model indicated that exchanging inorganic for organic sources only decreased fecal Zn excretion by 19 mg/d. For pigs fed Zn diets below the requirement, 61% of Zn intake was excreted in feces, increasing to 82.5% when Zn exceeded requirements. Similarly, Cu excretion increased from 68.4% to 87.9% as intake surpassed requirements. For Fe, when dietary levels exceeded requirements, 61.9% of intake was excreted. For K and S, which are primarily excreted via urine, models predicted total mineral excretion (urine + feces). The model estimated that 80% and 57.7% of K and S intake, respectively, were excreted. The predictive models developed in this study provide a valuable tool for estimating mineral excretion in pigs. Such models are essential for evaluating environmental impacts associated with different feeding strategies. By allowing nutritionists and producers to adjust diets, these models support sustainable feeding strategies aimed at minimizing mineral excretion and reducing the environmental footprint of swine production. In conclusion, mineral intake is the primary driver of mineral excretion in pigs, with excretion increasing as dietary intake rises.