doi:10.1016/j.heliyon.2020.e03529engAbecia, José A.Keller, MatthieuChemineau, PhilippeDelgadillo, José A.Light-induced sexually active rams provoke LH preovulatory surges and enhances LH concentrations in ewes after progestagen treatmentART-2020-117269The effect of the introduction of sexually active rams in spring on LH secretion in ewes after progestagen treatment has been studied. Two rams were induced into a sexually active state by exposure to 2 months of long days (16 h of light/d) from 1 January (SAR), and another 2 rams were exposed to the natural photoperiod, so that they were not sexually activated in spring (control; C). At the end of the long-day period, rams were returned to natural photoperiod conditions. Fifteen ewes synchronized in estrus by intravaginal sponges were assigned to three groups at sponge withdrawal (hour 0): SAR (n = 5), exposed to SAR rams; C (n = 5), exposed to C rams, and ISO (n = 5), kept isolated from rams. Twenty-four hours after pessary removal (hour 0), rams were introduced into the SAR and C groups. Three SAR ewes presented preovulatory LH surges; the proportion was significantly (P < 0.05) higher in this group (3/5) than in the others (C: 0/5, ISO: 0/5). SAR introduction induced a more marked (P < 0.05) increase in mean LH plasma concentrations (before rams: 1.34 ± 0.19; after rams: 6.94 ± 2.66 ng/ml) than C (before: 0.96 ± 0.29; after: 3.60 ± 1.44) or ISO (before: 1.26 ± 0.42; after: 2.14 ± 1.36) groups, and significantly (P < 0.05) higher plasma LH levels after ram introduction. In conclusion, only light-treated sexually activated rams induced LH preovulatory surges in ewes in the seasonal anestrus, when ewes are synchronized with progestagen treatment in the absence of eCG.2020http://zaguan.unizar.es/record/8854110.1016/j.heliyon.2020.e03529http://zaguan.unizar.es/record/88541oai:zaguan.unizar.es:88541Heliyon 6, 3 (2020), e03529 1-4by-nc-ndhttp://creativecommons.org/licenses/by-nc-nd/3.0/es/info:eu-repo/semantics/openAccess