[en] Three experiments were performed to determine the effect of postpartum time interval, the influence of parity (primimarous vs multiparous), and lamb weaning on the response of postpartum ewes to oestrus synchronization/induction treatments during the breeding season. In the Experiment 1 ewes were treated with an 8-days medroxyprogesterone priming and 350 IU of eCG, starting 14-18 (EPP), 24-30 (MPP), or 42-48 (LPP) days postpartum. More EPP than LPP ewes were marked by rams (p &lt; 0.05), but conception rate was similar. In Experiment 2, 36 primiparous and 47 multiparous ewes that lambed during autumn received a 12-days medroxyprogesterone treatment followed by the introduction of rams. Ewes that came into oestrus, and that had a corpus luteum on Day 5 was greater in multiparous than in primiparous ewes (p = 0.04 and p = 0.03 respectively). Pregnancy rates on Day 35 and on Day 90 were similar. Experiment 3 was conducted with 26 ewes that remained with their lambs suckling during all the experiment, and 26 that were weaned ~27 days after birth, 3 days before the introduction of the rams. There were no differences on the percentage of ewes that came into oestrus, or the conception rate. We concluded that in postpartum ewes that had lambed during the breeding season: (1) is possible to induce fertile oestrus during early postpartum; (2) the early response was greater in multiparous rather than in primiparous ewes, although after a 35 d-breeding period differences disappeared and (3) weaning lambs early before stimulation did not improve the response.

[es] Se realizaron 3 experimentos para determinar el efecto del tiempo posparto, de la paridad (prim&iacute;paras-mult&iacute;paras) y el destete sobre la respuesta de ovejas posparto a una sincronizaci&oacute;n/induccci&oacute;n de celos durante la estaci&oacute;n reproductiva. En el Experimento 1 se trat&oacute; a las ovejas con medroxiprogesterona durante 8 d&iacute;as y eCG (350 IU), a los 14-18 (EPP), 24-30 (MPP), o 42-48 (LPP) d&iacute;as posparto. M&aacute;s ovejas EPP que LPP (p &lt; 0,05) manifestaron celo, siendo la tasa de concepci&oacute;n similar. En el Experimento 2 se utilizaron 36 ovejas prim&iacute;paras y 47 mult&iacute;paras que parieron durante oto&ntilde;o, y recibieron un tratamiento con medroxiprogesterona seguido de la introducci&oacute;n de carneros. El porcentaje de ovejas en celo, y ovejas que ovularon a los 5 d&iacute;as fue mayor en las mult&iacute;paras que en las prim&iacute;paras (p = 0,04 y p = 0,03 respectivamente); la tasa de pre&ntilde;ez fue similar. En el Experimento 3 se utilizaron 26 ovejas que permanecieron con sus corderos lactando durante todo el experimento, y 26 que fueron destetados a ~27 d&iacute;as posparto, 3 d&iacute;as antes de la introducci&oacute;n de los carneros. No hubo diferencias en los porcentajes de ovejas en celo, ni en la tasa de concepci&oacute;n. Se concluy&oacute; que en ovejas postparto que parieron durante la estaci&oacute;n reproductiva: (1) fue posible inducir celos f&eacute;rtiles durante el posparto temprano; (2) la respuesta temprana fue mayor en ovejas mult&iacute;paras que en ovejas prim&iacute;paras, y (3) el destete temprano realizado poco tiempo antes de la introducci&oacute;n de los carneros no mejor&oacute; la respuesta reproductiva.