Effect of estrus synchronization with norgestomet on the integrity of oocytes from persistent follicles in beef cattle

Our objective was to determine whether oocyte integrity is compromised when oocytes are recovered from progestogen-induced persistent follicles. Beef cows were presynchronized using PGF(2 alpha) (PGF). Cows detected in estrus after PGF were assigned to either NOR (one 6-mg norgestomet implant for 10 d starting on d 16 of cycle; day 0 = estrus; n = 112) or CON (control, no implant [n = 128] and presynchronized 8 d later than NOR). All cows receive d 25 mg of PGF at the end of treatment (NOR, d 26; CON, d 18). Treatments p roduced persistent preovulatory follicles (NOR) or normal preovulatory-size follicles (CON), which were measured via ultrasonography 1 d before slaugh ter. Ovaries were collected from all animals (NOR, d 27; CON, d 19) along w ith random (RAN) ovaries fi om cattle slaughtered on the same days. Cumulus oocyte complexes (COC) were aspirated from the preovulatory follicles with recovery rates of 63% across treatments. Small follicles (2 to 7 mm diamet er) from NOR, CON, and RAN cows were also aspirated to recover COG. Preovul atory follicles were larger (19.5 +/- .9 vs 13.6 +/- .4 mm, P < .05), serum Pq was lower (.4 +/- .1 vs 3.9 +/- .2 ng/mL, P < .05), and serum E-2 was h igher (28.7 +/- 1.6 vs 7.6 +/- .8 pg/mL, P < .05) in NOR than in CON cows. Cumulus oocyte complexes recovered from preovulatory follicles (62 NOR, 64 CON) were matured, fertilized, and cultured in vitro for comparison of embr yonic development. A subset (24 NOR, 34 CON) of COC were assigned morpholog ical quality grades. A separate set of recovered COC (10 NOR, 15 CON) was f ixed within 1 h after recovery for assessment of the stage of meiosis. Trea tments did not differ for oocyte quality grade or stage of meiosis. However , COC from NOR cows had more layers of cumulus cells (P < .05), and more of those COC had undergone cumulus expansion (29.2 vs 5.9%, P < .05 for NOR v s CON, respectively). Development of cleaved embryos to the morula and blas tocyst stages from preovulatory follicles (22.6% NOR, 18.9% CON) or small f ollicles (42% NOR, 40% CON, 42% RAN) did not differ with treatment. Oocyte quality and in vitro developmental competence were not compromised for oocy tes from induced persistent follicles compared with oocytes from normal pre ovulatory follicles. Increased expansion of cumulus cells associated with o ocytes from progestogen-induced persistent follicles may be relevant to the reduction of in vivo fertility associated with such follicles.