Year-to-year variation (2017–2022) in the semen parameters of ejaculates from donor candidates and accepted donors. (A) Ejaculate volume, (B) sperm concentration, and (C) total sperm count. Marginal means ± 95% CL are plotted here for donor candidates (n = 6758) and accepted donors (n = 1839), calculated from models that accounted for the man’s age, monthly mean high temperature, and Danish city (see also Supplementary Tables S3, S4, and S5).