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Background:Heifers not used as breeding stock are often implanted with steroids to increase growth efficiency thereby altering hormone profiles and potentially changing the environment in which ovarian follicles develop. Because bovine granulosa cell culture is a commonly used technique and often bovine ovaries are collected from abattoirs with no record of implant status, the objective of this study was to determine if the presence of an implant during bovine granulosa cell development impacts follicle stimulating hormone-regulated steroidogenic enzyme expression. Paired ovaries were collected from 16 feedlot heifers subjected to 1 of 3 treatments:non-implanted (n=5), Revalor 200 for 28 d (n=5), or Revalor 200 for 84 d (n=6). Small follicle (1 to 5 mm) granulosa cells were isolated from each pair and incubated with phosphate buffered saline (n=16) or 100 ng/mL follicle stimulating hormone (n=16) for 24 h. Results:Granulosa cells of implanted heifers treated with follicle stimulating hormone produced medium concentrations of progesterone similar (P=0.22) to non-implanted heifers, while medium estradiol concentrations were increased (P