The aim of this work was to evaluate the effects of exposure to artificial long days at an early age, or rearing in the presence of sexually activated adult rams, on sexual activity, testicular growth and plasma testosterone levels of autumn‑born Merino ram‑ambs in spring. Forty lambs born in September were assigned at 6 months of age to one of these four groups: DL (n = 10), exposed to 2 months of long days (16 h light/day; 1 February‑31 March); MAA (n = 10), housed since April 1st with two adult males, sexually activated by artificial photoperiod; MAC (n = 10), with two non-activated adult rams, and A (n = 10), isolated from adult rams during the whole experiment. No significant differences were observed between groups for live weight, body condition, and scrotal perimeter. Plasma testosterone concentration was similar until 7.5 months of age, when all groups showed a marked decrease. From that moment, group A increased its concentrations, unlike the rest of the groups (P < 0.05), at the end of the experiment. Group A showed a greater sexual activity in individual behavioral tests (P < 0.05) than the groups raised with adult males, which needed more time to achieve the first ejaculation (P < 0.05). In conclusion, Merino sheep born in autumn, reared from weaning in isolation from other adult males, showed a more intense sexual activity in spring than lambs reared in the presence of adult males, whether or not these were sexually activated in spring.

Arrebola‑Molina FA, Castillejo‑Lacalle E, Borjas‑Muñoz F, Querino‑Santiago FJ, Redondo‑Cardador FC, Abecia JA (2022). Efecto del modo de cría de borregos de raza Merina nacidos en otoño sobre su actividad sexual, desarrollo testicular y secreción de testosterona en primavera. ITEA‑Información Técnica Económica Agraria 118(1): 36-47. https://doi.org/10.12706/itea.2021.012