Plasma progesterone concentrations in cycling and in ovariectomised red deer hinds: The effect of progesterone supplementation and adrenal stimulation

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Peripheral plasma progesterone was measured in intact and ovariectomised red deer hinds in three experiments to investigate endogenous concentrations during the oestrous cycle, concentrations achieved by exogenous administration and following adrenal stimulation. Daily samples revealed that seasonal anoestrus was characterised by low (<0.2 ng/ml) progesterone levels. A short period of elevated progesterone concentrations (up to 0.9 ng/ml) preceded first oestrus. Progesterone concentrations increased to reach peak levels (2.2–3.1 ng/ml) in the late luteal phase of the cycle followed by a rapid decline with luteal regression (Experiment 1). In Experiment 2, exogenous progesterone treatments administered to ovariectomised hinds for 14 days gave mean plasma progesterone concentrations of 0.0, 1.2, 2.2 and 1.5 ng/ml for control, intravaginal controlled internal drug-releasing sheep (CIDR-S) device containing 340 mg (9% w/ w) progesterone. CIDR-S containing 465 mg (12% w/ w) progesterone and hogget CIDR (CIDR-H) containing 330 mg (12% w/ w) progesterone, respectively. All three CIDR treatments produced similar mean patterns of plasma progesterone concentrations with peak levels of up to 3.1 ng/ml occurring 1 day after CIDR insertion. Concentrations gradually declined thereafter, eventually averaging about 1 ng/ml on the last day of insertion. On some occasions, hinds with no progesterone devices were found to have up to 3.3 ng/ml plasma progesterone. In Experiment 3, administration of synthetic ACTH significantly elevated plasma progesterone concentrations up to 1.3 ng/ml, 15–30 min following administration. Plasma cortisol reached concentrations of approximately 40 ng/ml, 15–90 min following administration. These results indicate that as in other farmed animals, plasma progesterone in the hind is elevated prior to the first oestrus of the breeding season, and the oestrous cycle comprises distinct luteal and follicular phases. While all the exogenous progesterone treatments used significantly elevated plasma progesterone concentrations, none maintained concentrations at levels similar to those recorded during the luteal phase. The results also indicate that the adrenal gland may be a significant source of progesterone in the red deer hind.