Effect of the stage of pregnancy and post-partum on the number of gonadotrophin responsive follicles in ewes

The present study was designed to study follicular growth and its interacti ons with the corpus luteum of pregnancy in sheep during early, middle and l ate pregnancy and during postpartum anestrus. Ewes with 1 or 2 corpora lute a in one ovary were selected from a larger group of Serres ewes. All pregna nt ewes were randomly allocated to two groups, with 10 to 12 ewes per group . Ewes of Group I were treated with 750 IU hCG at Day 25 or 45 or 70 or 100 or 125 of pregnancy. In Group II, ewes were treated with a combination of 1000 IU PMSC + 750 IU hCG either at Day 25 or 45 or 70 or 100 of pregnancy. The results demonstrated the presence of gonadotrophin-responsive follicle s during early pregnancy (Days 25 to 45), reduction of their number during mid-pregnancy (Days 70 to 100), and their disappearance during late pregnan cy (Day 125). Administration of hCG to Serres ewes at 10 and 20 days postpa rtum induced ovulation of a high proportion of ewes at 10 days postpartum ( 62%) with a further increase observed at 20 days postpartum (75%). During p regnancy, as well as during the postpartum period, there was no significant difference in the number of ovulations induced according to the location o f the corpus luteum of pregnancy. These data demonstrate that the presence of the corpus luteum of pregnancy does not affect the number of gonadotroph in-responsive follicles until Day 100 of pregnancy. However, during late pr egnancy such follicles were no longer present in the ovaries. Gonadotrophin -responsive follicles were again present as soon as Day 10 postpartum. (C) 2001 by Elsevier Science Inc.