Anim. reprod. sci. Anim. reprod. sci. Changes in melatonin concentrations in seminal plasma are not correlated with testosterone or antioxidant enzyme activity when rams are located in areas with an equatorial photoperiod Carvajal-Serna M. Torres-Ruda F. Cardozo J.A. Grajales-Lombana H. Cebrián-Pérez J.Á. Universidad de Zaragoza Muiño-Blanco T. Universidad de Zaragoza Pérez-Pé R. Universidad de Zaragoza Casao A. Universidad de Zaragoza 2019 research-article