This study investigated the effect of a progesterone containing intravaginal CIDR (Controlled Internal Drug Releasing) device on plasma progesterone and luteinizing hormone (LH) concentrations during 14-day device insertion and the subsequent oestrous cycle of fallow deer (Dama dama). Blood samples were collected from 4 entire does at 20 minute intervals for periods of 8-12h on three occasions following device insertion (i.e. insertion, mid-treatment and withdrawal) and on Days 0, 5, 12 and 19 of the subsequent oestrous cycle. Plasma was analysed for progesterone and LH concentrations by radioimmunoassay. Plasma progesterone values were elevated (>6 ng/ml) and LH values reduced (<1 ng/ml) during device insertion relative to pre-insertion values. Plasma LH concentrations were highest on Day 0 of the oestrous cycle, with a marked increase in the pulse amplitude. One doe exhibited a pre-ovulatory LH surge. Plasma progesterone increased from <0.5 ng/ml on Day 0 to 1.5-4.2 ng/ml on Day 12 (luteal phase) and high amplitude progesterone pulses were exhibited by all does on Day 19 (onset of luteolysis). The study has demonstrated that CIDR devices deliver sufficient progesterone to inhibit ovulation and the declining plasma LH concentrations during device insertion support a hypothesis of negative feedback by progesterone on LH secretion.
Proceedings of the New Zealand Society of Animal Production, Volume 53, , 355-358, 1993
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