Endocrine changes and recovered oocytes were evaluated during 16 wk of ultrasound-guided transvaginal follicular aspiration (TVF A) and prior to and following administration of GnRH at the cessation ofTVFA. Previously aspirated (PAC, n = 4) and non-aspirated, non-lactating (AC, n = 4) Holstein cows were subjected to 16 wk of twice-weekly TVFA. Four control cows (OAC) were aspirated one time only at the final TVFA session (wk 16). The PAC and AC cows averaged 3.4 ± 1.2 (± SE) and 6.8 ± 1.2 oocytes/session, respectively. Progesterone in OAC was 4.5 ± .2 ng/mL before TVFA, while the PAC and AC averaged .5 ± .2 and .3 ± .2 ng/mL, respectively, at wk 16. LH was 1.0 ± .2 ng/mL at wk 16 and increased to 7. 5 ± .1 ng/mL after GnRH. Follicle numbers after GnRH varied most among treatment groups for follicles < 9 mm. The LH concentrations for the period following the final TVF A session were associated with increased numbers of peaks and peak frequencies in the PAC when compared to OAC, and the interval between peaks is increased in the PAC and AC. These results suggest that long-term TVF A affects progesterone and LH profiles and ovarian dynamics in cows. A second objective was to determine if platelet-derived growth factor (PDGF-BB) and leukemia inhibitory factor (LIF) exhibit a stimulatory effect during in vitro co-culture with Buffalo Rat liver cells (BRL). Oocytes were matured in transit, fertilized in vitro, and embryos were co-cultured with BRL cells for 7 d. The treatment groups were as follows: treatment 1 = 1 ng/mL PDGF-BB, where PDGF-BB is the human recombinant homodimer of the B chain; treatment 2 = 1 ng/mL LIF; treatment 3 = .5 ng/mL PDGF-BB + .5 ng/mL LIF; treatment 4 = 1 ng/mL PDGF-BB + 1 ng/mL LIF; and treatment 5 = control group cultured in modified TCM 1 99 alone. Morulae and blastocyst development was decreased with the addition of 1 ng/mL PDGF-BB (12.4%) and with the addition of .5 ng/mL PDGF-BB and .5 ng/mL LIF (11.7%) when compared with control development (23.3%). These results indicate the addition of PDGF alone and low amounts of PDGF and LIF to the BRL cell co-culture system for bovine zygotes provides an inhibitory effect on the developmental rates. A combination of 1 ng/mL PDGF and 1 ng/mL LIF and LIF alone exerted a neutral effect on development, suggesting BRL cell co-culture is not enhanced by addition of these growth factors. / M.S.