Could metal exposure affect sperm parameters of domestic ruminants? A meta-analysis

During the last decade, environmental toxicants have been considered a potential cause for declining sperm quality. Toxic metals are not easily degraded and may accumulate along the food chain, which may negatively impact the semen quality of animals. In this framework, we conducted a meta-analysis to determine whether exposure to Al, As, Cd, Cr, Co, Cu, Fe, Mg, Mn, Hg, Ni, and Pb affects sperm and andrological parameters of domestic ruminants. We extracted 217 independent comparisons from 39 published articles selected from PubMed, Web of Science, and Scopus. Our findings showed that metal exposure reduced sperm viability (d₊₊ = - 1.04, df 51, CI - 1.47 to - 0.61) and motility (d₊₊ = - 0.83, df 104, CI -1.19 to - 0.51) by increasing oxidative metabolites production (d₊₊ = 2.98, df 20, CI 1.95-0.11). Sperm viability and motility were affected by Cd, As, Hg, and Fe contamination. Metal poisoning impaired andrological parameters (d₊₊ = - 0.83, df 17, CI - 1.10 to - 0.02) after arsenic intake using 3 and 5 mg L^-1 orally. Detrimental effects on spermatozoa were mostly observed after in vitro incubation with metals using concentrations < 2.99 mg L^-1 up to 24 h. The review limitations were the heterogeneity of methodologies used in the studies and absence of investigations focused on the effect of Al, Co, Cr, Mg, and Ni exposure on sperm parameters in ruminants. Nevertheless, our findings contribute to understanding the impact of metal exposure on reproductive parameters in ruminants, with potential damage to their fertility.