Zinc Supplementation on Growth Performance, Mineral Metabolism and Nutrient Digestibility in Lambs: a Systematic Review and Dose-response Meta-analysis.

The effects of dietary zinc (Zn) supplementation on lambs fed diets without added Zn remain controversial, and the precise nature and extent of the associations between Zn administration and lamb responses are not fully understood. To address this, a comprehensive systematic review and dose-response meta-analysis was conducted to explore the effects of Zn supplementation on growth performance, mineral metabolism, and nutrient digestibility. Initially, 3169 studies were identified through comprehensive database searches using relevant keywords. Following a two-stage screening process, 30 eligible articles were selected based on predefined criteria and used in the current meta-analysis. The one-stage random-effects model was utilized in this meta-analysis, with sensitivity analyses conducted to evaluate the robustness of the derived effect sizes. The results showed nonlinear relationships between Zn supplementation and performance parameters. Optimal Zn levels were identified: approximately 28.51 mg/kg DM for maximum dry matter intake, 37.84 mg/kg DM for highest weight gain, and 42.00 mg/kg DM for best feed conversion ratio. Linear increases in fecal and urinary Zn, and a decrease in apparent Zn absorption, were observed with increasing Zn supplementation (P < 0.05). Zinc supplementation up to 53 mg/kg DM enhanced Zn retention, and up to 107 mg/kg DM, increased liver Zn concentration, with the highest concentration at 50.59 mg/kg DM. Zinc supplementation also affected copper and iron concentrations in various tissues. Specifically, it decreased pancreatic copper up to 22 mg/kg DM but increased it above 50 mg/kg DM. In kidney tissue, copper concentration increased linearly with Zn supplementation from 76 to 150 mg/kg DM, while in liver tissue, it decreased from 42 to 150 mg/kg DM. Heart tissue iron concentration increased up to 24 mg/kg DM but decreased from 41 to 150 mg/kg DM, with the highest concentration at 16.31 mg/kg DM. Zinc supplementation at 28.28 and 20.88 mg/kg DM increased total concentration of rumen volatile fatty acids and dry matter digestibility, respectively. However, final weight, carcass weight, nitrogen metabolism, Zn levels in heart, pancreas, and kidney tissues, copper levels in heart tissue, iron levels in pancreas and liver tissues, and the digestibility of most dietary fractions (organic matter, crude protein, NDF, and ADF) were not affected (P > 0.05). In summary, the findings of this meta-analysis generally align with NRC guidelines; this study underscores the necessity of precise Zn supplementation to optimize lamb productivity and mitigate potential adverse effects.