Context. In subtropical latitudes, most goats are managed in semi-extensive management systems, eating only available vegetation. Underfeeding is common during the dry season and may reduce the endocrine and sexual activities of male goats. Aims. The aim of the study was to determine plasma testosterone concentrations, sexual behaviour and sperm production of male goats kept in a semiextensive management system for 12 months, from March to February. Methods. Control males were placed indoors and were well nourished (n = 5). Experimental males were placed in a flock and grazed daily with females for 7 h, eating only natural vegetation (n = 5). Experimental males were fitted with an apron to prevent mating during the study. Plasma testosterone concentrations were determined every 2 weeks. Sexual behaviour and sperm production were determined in May and June (beginning of breeding season), August and October (middle of season), and November and December (end of season). Key results. Plasma testosterone concentrations were higher (P < 0.05) in control than experimental males in June and from August to December. The percentage of males refusing to ejaculate was lower (P < 0.05) in control than experimental males throughout the study. Total number of spermatozoa per ejaculate was higher (P < 0.05) in control than experimental males in May, June, November and December. Sperm progressive motility was higher (P < 0.05) in control than experimental males in May and June and from October to December. Conclusions. The results indicate that male goats in a semi-extensive management system have lower plasma testosterone concentrations, sexual behaviour, and sperm quantitative and qualitative production than those in a confined management system.