The aim of this work was to study whether or not the presence of previously sexually stimulated males by melatonin and artificial photoperiod may reduce seasonal anestrus in sheep, keeping their ovulatory activity in spring. Vasectomized rams were exposed to 2 months of long days and 3 melatonin implants (treated rams, n=8), or remained under natural light conditions (control rams, n=2). Ewes were divided into two groups, and were kept in contact, in different houses, with the treated (n=16) or the control rams (n=15) from February to July. Oestrus was recorded every day through marks in the ewes’ rumps from harnesses, and ovarian activity through weekly blood samples. Most of the ewes exposed to treated rams (14/16) presented oestrus during the studied period. The control group presented a higher percentage of silent ovulations than the treated group in March (P<0.05) and April (P<0.01). In conclusion, the presence of sexually activated rams by artificial photoperiod and melatonin in spring can lead to an increased oestrous activity of the ewes.