title: Effect of norgestomet on peripheral levels of progesterone and estradiol-17beta in beef cows.
abstract: Peripheral levels of progesterone and estradiol 17beta were quantified in 27 cycling cows following administration of a single Hydron ear implant (G. D. Searle and Co.) containing 2, 4 or 6 mg norgestomet or controls which received no implant. Implants were inserted subcutaneously in the ear on day 15 of the estrous cycle (day of estrus = day 0) and removed 9 days later. The 4 mg (seven of seven cows) and 6 mg (six of six cows) implants suppressed estrus; however, three of eight cows in the 2 mg group exhibited estrus prior to implant removal. The 6 mg implant group had a significantly longer interval from implant removal to estrus than either the 2 or 4 mg group. Failure to detect differences in the rate at which progesterone declined indicated norgestomet treatment did not affect normal corpus luteum regression. Estradiol levels rose at a similar rate approaching estrus in all treatments. There was no indication of increased endogenous estradiol levels due to norgestomet treatment.
authors.affiliation: Division of Animal Science, University of Wyoming, Laramie, Wyoming 82071, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Moseley
authors.forename: D W
authors.initials: DW
authors.lastname: Forrest
authors.forename: C C
authors.initials: CC
authors.lastname: Kaltenbach
authors.forename: T G
authors.initials: TG
authors.lastname: Dunn