In vivo oocyte recovery and in vitro embryo production from bovine donors aspirated at different frequencies or following FSH treatment

The effects of frequency of follicular aspiration and treatment of donor ca ttle with FSH on in vivo oocyte recovery and in vitro embryo production wer e studied. Simmental heifers (n = 24) formed 8 replicates of 3 treatments i n which oocyte donors were aspirated 1) once a week, 2) twice a week, or 3) once a week following treatment with FSH for 3 d prior to aspiration. Oocy tes were graded, washed, matured for 20 to 24 h and then inseminated with f rozen/thawed semen from a single sire, followed by co-culture on granulosa cell layers. Embryo development was observed until Day 7 after insemination ; Significantly fewer follicles per heifer per week were counted (14.7 +/- 2.3 vs 27.4 +/- 3.1 vs 23.1 +/- 2.8) and aspirated (12.0 +/- 2.0 vs 21.8 +/ - 2.7 vs 20.1 +/- 2.6) in heifers on the once-weekly than twice-weekly aspi ration treatment (P<0.01) or on the once-weekly aspiration after FSH treatm ent (P<0.05). There were no significant differences between treatments in t he total number of oocytes recovered per week (5.6 +/- 1.2 vs 8.9 +/- 1.5 v s 6.1 +/- 1.2), but significantly more oocytes per heifer per week recovere d from animals treated with FSH were graded Category 1 (2.8 +/- 0.4), i.e., >4 layers good cumulus with a clear, even cytoplasm, than from animals asp irated once (0.9 +/- 0.2; P<0.01) or twice a week (1.5 +/-: 0.3; P<0.05). T he number of transferable morulae plus blastocysts produced per heifer per week was higher from animals aspirated twice a week (2.4 +/- 0.4; P<0.05) o r once a week following FSH treatment (2.1 +/- 0.4; P<0.05) than from anima ls aspirated once a week without FSH treatment (1.0 +/- 0.3). In conclusion , FSH treatment of bovine oocyte donors aspirated once a week enabled a sim ilar number of transferable embryos to be produced per donor week as aspira tion twice a week without FSH treatment. These 2 treatments produced twice as many transferable embryos per donor week as aspiration once a week witho ut FSH treatment. (C) 1999 by Elsevier Science Inc.