Semen characteristics versus testosterone levels.

<p>Semen characteristics versus mean peripheral plasma testosterone levels (“T”; in nmol/L). Mean sperm number (A) after exposure to mares versus T during exposure to mares (tau = 0.45, p = 0.04), and (B) after exposure to stallions against T during exposure to stallions (tau = -0.31, p = 0.19). (C) Mean VCL after exposure to mares against T during exposure to mares (tau = 0.18, p = 0.41), and (D) after exposure to stallions against T during exposure to stallions (tau = 0.49, p = 0.04). The analogous correlations between T and the other sperm velocity measures were never significant (|tau| always < 0.30, p always > 0.17). Stallions were either first exposed to stallions and then to mares (triangles) or vice versa (circles). The lines give the regressions to emphasize the direction of significant correlations.