ULTRASONICALLY GUIDED TRANSVAGINAL OOCYTE RECOVERY FROM CALVES TREATED WITH OR WITHOUT GNRH

We investigated the effect of GnRH given after gonadotropin stimulatio n on follicle growth and oocyte quality in young calves in a transvagi nal oocyte recovery program. A 60 mg MPA pessary was inserted into eac h of nineteen 5-mo-old Friesian calves for 7 d; on Day 5 they received 140 mg, sc FSH (Folltropin) and 200 IU, im PMSG and on Day 8 ten of t he calves received 40 mu g, im GnRH (Fertagyl). Follicles were measure d and aspirated on Day 9 using an ultrasound unit with a 6 MHz transva ginal probe (Toshiba). Oocytes from individual calves were recovered, graded and cultured in maturation media for 2 h (+GnRH group) or 22 h (-GnRH group), then fertilized and cultured for 6 d in SOF containing 0.8% BSA and amino acids. Oocyte viability (Class A,B or C) and embryo morphology were recorded. This procedure was repeated on the 19 calve s plus 5 others 1 mo later, after random allocation to their respectiv e groups. Approximately 70% of the calves responded to gonadotropin st imulation (>2 follicles over 5 mm in diameter). Calves receiving GnRH tended to have both a higher number of follicles >2 mm in diameter (27 .1 vs 18.7) and of aspirated follicles (22.0 vs 14.1); however, there was a large variability between individuals (0 to 83 follicles and 0 t o 73 aspirated). The total number of oocytes collected (10.8 vs 10.9) was not affected by GnRH treatment, probably due to the poor recovery rates in the highly stimulated calves from the +GnRH group, but GnRH d id improve the proportion of viable oocytes (6.5 vs 4.1) due to a lowe r number of Class E oocytes (1.4 vs 4.5; P<0.05). In the GnRH group, 4 0% of the viable oocytes had matured at the time of collection versus 0% in the group not treated with GnRH. The necessity of different cult ure runs between times and treatments prevented any meaningful compari son between groups for embryo development. Following the transfer of 1 9 morula/blastocyst-stage embryos to recipients, 3 pregnancies were de tected by ultrasound examination on Day 60, with 1 oocyte originating from the +GnRH group and 2 from the -GnRH group. (C) 1998 by Elsevier Science Inc.