Effects of Organic Zinc on the Growth Performance of Weanling Pigs: A Meta-analysis

Supplementation of feed with organic zinc (Zn) has long been discussed as an alternative to inorganic Zn in pigs, but its effects on growth performance are mixed. This meta-analysis was conducted to provide a comprehensive evaluation of the influence of organic Zn on the growth performance of weanling pigs, on the basis of average daily gain (ADG), average daily feed intake (ADFI), and feed to gain ratio (F/G). We screened the PubMed and Web of Science databases (published before December 31, 2022; limited to English) systematically and contrasted organic Zn supplementation with inorganic Zn supplementation. There were 680 retrievals of studies, of which 16 (1389 pigs, 37 records) were eligible to analyze. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated using a random-effects model. The subgroup analysis was classified as organic Zn source (Zn-amino acid (Zn-AA), Zn-glycine (Zn-Gly), Zn-methionine (Zn-Met), Zn-Lysine (Zn-Lys), proteinate complex Zn (Zn-Pro), chitosan-Zn (Zn-CS) or Zn-lactate (Zn-Lac)) and Zn additive dose (low, medium, or high, i.e., lower than, equal to or higher than the requirement of NRC). Organic Zn addition in the weaning phase increased the ADG (P<0.001) and the ADFI (P=0.023) and decreased the F/G (P<0.001). Specifically, for the organic sources, only Zn-CS supplementation presented significant effects on the ADG (P<0.001), ADFI (P=0.011), and F/G (P<0.001). Moreover, medium-dose organic Zn supplementation had positive effects on ADG (P=0.012), ADFI (P=0.018), and F/G (P<0.001). Our results indicate that organic Zn added to diets greatly improves the growth performance of weanling pigs.