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Summary. When female tammars carrying dormant blastocysts were injected with progesterone at the time of removal of their pouch young the development of the fetus was advanced and parturition occurred 5 days earlier than in the control tammars. In these tammars the prolactin pulse was also advanced by 5 days but the usually concomitant fall in progesterone was not. In non-pregnant tammars similar injections of progesterone did not advance the subsequent fall in progesterone, oestrus, or the LH pulse. In non-pregnant tammars injected with ovine prolactin on Day 26, to mimic the prolactin pulse, plasma progesterone was reduced to basal levels within 12 h, significantly earlier than in controls. Conversely, in 5 pregnant and 1 non-pregnant tammar injected with ovine prolactin on Day 23, to mimic the condition induced by advancing the time of parturition with progesterone, the decline in plasma progesterone was not advanced and the endogenous prolactin pulse, parturition, post-partum ovulation and the LH pulse all occurred after intervals similar to those of controls.

The results support the view that the fetus is associated with the pre-partum prolactin pulse in maternal plasma and that a prolactin pulse at this stage is luteolytic in non-pregnant tammars.

Keywords: tammar; fetus; parturition; prolactin

Summary. Two experiments, each using 8 animals, were conducted in the non-breeding and breeding seasons, respectively, and each animal was injected with 4 different doses of oestradiol benzoate over 4 trials. The resulting physiological concentrations of plasma oestradiol caused depression of both LH and FSH values. The highest dose elicited a biphasic response in LH with a pulse-like surge at 24 h after injection. There was no significant difference between the response of either hormone at the two times of the year and it is concluded that, in tammars, there is no seasonal difference in the responsiveness of the hypothalamus/pituitary to the negative feedback effect of oestradiol.

Summary. Oestradiol-17β was measured in plasma and follicular fluid by a radioimmunoassay validated for the tammar. Plasma was sampled from the peripheral circulation and both utero-ovarian veins to assess the contribution of oestradiol from the corpus luteum in one ovary and from the Graafian follicle in the other during late pregnancy, parturition, post-partum oestrus and ovulation. Concentrations of oestradiol in the peripheral plasma and in the vein draining the CL remained < 5 pg/ml on all days except the day of parturition, when they were 12·7 pg/ml and 14·3 pg/ml respectively. Mean oestradiol concentration in the vein draining the Graafian follicle was significantly higher than the mean peripheral concentration on Days 24–27. The highest average concentration (36·5 pg/ml) occurred on Day 27 coincident with parturition and before oestrus. These latter concentrations were significantly correlated with the concentration and total oestradiol in the fluid of the preovulatory Graafian follicle (r = 0·73 and r = 0·82 respectively), thus providing strong evidence that the Graafian follicle is the main source of oestradiol in the peripheral circulation at this time.

Summary. Concentrations of oestradiol-17β, progesterone, and luteinizing hormone (LH) were measured in plasma collected at 6- to 12-h intervals from tammars around the time of parturition and post-partum oestrus. Parturition occurred on Day 26 or 27 after reactivation of lactation-delayed pregnancy and coincided with a precipitous decline in progesterone levels. A sharp rise in oestradiol, from basal concentrations of < 10 pg/ml to a peak of 13 to 32 pg/ml, as well as oestrus, followed the drop in progesterone by 8·3 and 9·8 h, respectively. The LH surge was dependent on the oestradiol rise and followed it by 7 h. Ovulation followed mating by about 30 h and the LH surge by 24 h. Removal of the ovary with the large Graafian follicle prevented the oestradiol rise, oestrus and the LH surge, but not parturition. Peripartum changes in peripheral oestradiol do not appear to be involved in initiation of parturition but the oestradiol rise and associated change in the oestradiol:progesterone ratio are important signals for post-partum oestrus and the LH surge.