The ram’s fertility is a variable of high importance, since it contributes to improving productivity and, therefore, to improving the economic efficiency of the herds. In the male, the spermatozon contributes 50 % of the genetic information of the individual, which is why the physical and physiological events involved in the process of spermatogenesis are important; also, the variations through time of the testicular diameter and development and seminal production, which have a close relationship to the reproductive efficiency and are associated to other factors, such as the photoperiod (reproductive season versus seasonal anestrus season), nutrition (energetic balance), and breed. The reproductive efficiency of the herds, in economic terms, is responsible for the success or failure of the farm. A principal factor that conditions this process through time is the productive seasonality (reproductive season, short days and seasonal anestrus, long days). That is, along the year rams experience strong changes in testicular physiology, which modifies the expression of various reproductive variables associated to fertility, and in order to evaluate this characteristic, not only must the photoperiod be taken into account, but also factors such as breed and nutrition.