Dietary factors influencing zinc excretion in pigs: a meta-regression analysis

Although several nutritional tables report Zn requirements for pigs, dietary Zn levels that exceed recommendations are commonly used to improve performance in nursery pigs. However, excessive Zn supplementation is a practice that has been recently regulated in different countries. Understanding the factors influencing Zn excretion is important for optimizing Zn utilization in swine production and mitigating regulations of its use. This review compiled data from 51 published studies to identify factors associated with Zn excretion using a principal component analysis and developed predictive models for fecal Zn excretion utilizing a meta-regression analysis. Because urine Zn excretion was negligible (around 2% of the total Zn excretion), fecal and total Zn excretion did not differ. The first two principal components (PC) accounted for 35.9% and 19.3% of the total database variance, respectively. PC 1 was primarily influenced by nutrient intake variables, including fiber, NE, nitrogen, and minerals, such as P, Ca, and Fe, as well as body weight and feed intake. PC 2 was dominated by Zn-related variables, including Zn intake, fecal Zn excretion, the difference between Zn intake and Zn requirements estimates from NRC, and added dietary Zn. Variables such as Mn, Cu, and lactose intake moderately contributed to both components, whereas the use of antibiotics, exogenous enzymes other than phytase, and acidifiers had a low impact on the variation explained by both components. Stepwise selection indicated that when pigs were fed at or below their Zn requirement estimate, Zn, P, and Fe intake significantly influenced fecal Zn excretion. However, when Zn intake exceeds the requirement estimate, Zn sources and Zn intake were the most influential variables. Regardless of the scenario, Zn intake was the primary determinant of fecal Zn excretion. The meta-regression analysis indicated that when pigs are fed at or below their Zn requirement, 61% of Zn intake is excreted in feces, increasing to 82% when Zn intake exceeds requirements. In conclusion, while Zn excretion is affected by multiple dietary factors, their contribution under practical conditions is relatively low, and Zn intake remains the primary determinant of fecal Zn excretion.