N OCIETY' - the Society for Reproductive Biology

--o121:.­.- ....:l~ S 8o b.O~54oI•IA critical number ofeggs stimulates prolactin secretion inmale emus during the breeding seasonJ. Van eleeff, E. Prendergast, D. Blache and G.B. Martin.Faculty of Agriculture (Animal Science), The University of Westem Australia, Nedlands 6907.Increasing concentrations of prolactin are seen in Winter in male emus which incubate a clutch ofeggs and in all male emus during seasonal fattening in Spring. The Spring stimulus for prolactinsecretion is increasing daylength, but photoperiod does not appear to playa direct role in Winter.Since the increases in prolactin concentrations in Winter are associated with incubation, wehypothesise that the stimulus is the presence of eggs.We collected blood samples fortnightly in Autumn and twice weekly in Winter from 6 singlemales and from males of 10 mating pairs of emus. Serum was assayed for prolactin and testosterone.Data were analysed for effect of time, sex, status (paired v single), incubating status, and daysrelative to incubation when appropriate.There were no differences in eitherFigure 1: Serum concentrations of testosterone andtestosterone or prolactin concentrations betweenprolactin in male emus which incubated (.) or did notincubate (0) during the breeding season. paired non-incubator males (n=5) and singlemales, and no effect of time for these groups(Fig. 1). In contrast, in incubator males (n=5),•I••e• • o105 119 133 147 161 175 189 203Julian Dayoboth hormones changed over time, withtestosterone decreasing and prolactin increasing.When these data are arranged relative to first dayof incubation (Fig. 2), testosterone was elevatedprior to incubation, and declined rapidly to nearthe limit of detection (0.06 ng/mL) within days ofthe start of incubation. Prolactin began toincrease prior to the start of incubation, and theprofile of prolactin secretion during clutchformation followed a sigmoidal curve describinga cubic function (Fig. 3). Increases were notevident until at least 6 eggs were present;prolactin concentration at this stage of clutchformation was 1.2 ± 0.5 ng/mL (mean ± SD).When 7 eggs were present, prolactin increased to3.1 ± 1.3 ng/mL (mean ± SD), exceeding 6 SD ofthe mean concentration for 6 eggs or less. Once 8or more eggs were present, prolactin further increased to 6.6 ± 1.8 ng/mL, exceeding by 13 the value?f. t?e SI? for 6.eggs or less. Thereafter, increasing number of eggs did not affect prolactin. EmusInItiated IncubatIon at clutch sizes 7 (n = 1), 8 (n = 3) or 12 (n = 1) eggs.For m~~ emus, stimulation of prolactin secretion in Winter requires the presence of eggs.However, a cntIcal number eggs m..ust fIrst ~e accumulated before the cue becomes effective.Figure 2: Serum concentrations of testosterone ( 0 ) andprolactin (. ) in individual incubator emus, relativeto day incubation began.Testosterone(nglmL)4o 0 ••~ oo~ooooo oo~Jt""".• •Prolactin(ng/mL)o ~ i ~ ~'rrsr'Ofiii i-84 -70 -56 -42 -28 -14 0 14 28 42 56Day relative to start of incubation1284oEffects of levonorgestrel on fertility in the tammar wallaby, Macropus eugenii.C. Nave, G. Shaw, R.V. Short, and M.B. RenfreeDepartment of Zoology, Melbourne University, Parkville 3052. Australia.INTRODUCTIONLevonorgestrel is a synthetic progestin, which provideseffective contraception in women. It has several modesof action but primarily it inhibits the hypothalamicpituitaryaxis, which in turn prevents ovulation.Macropodid marsupials are highly fecund, so theirnumbers are capable of increasing rapidly, causingconsiderable management problems in public parks andwildlife sanctuaries. In these semi-urban areas alternatemanagement techniques to culling and baiting aredesirable.The aims of this study are to test the efficacy oflevonorgestrel as a possible anti-fertility agent formacropodid marsupials, using tammar wallabies as amodel species.MATERIALS AND METHODSFemale tammar wallabies carrying pouch young (n=12)received a single - levonorgestrel implant (Leiras,Finland). Implants composed of thin-walled siliconetubing, sealed at each end with silastic adhesive were2.5mm in diameter, 4.3cm in length and contained75mg of levonorgestrel. Control implants consisting ofa hollow silicone tubing of the same length anddiameter as the levonorgestrel implants were placed infemale tammar wallabies carrying pouch young (n=12).Implants were inserted subcutaneously into the medialsubdermal connective tissue, between the shoulderblades. Pouch young were removed (RPY) 3 days afterinsertion, and the adult females given bromocriptine(25mg)(im) to synchronize reactivation of theirdiapausing blastocysts and initiate the 1 st cycle.Wallabies were checked daily 25-31 days followingpouch young removal, for birth and/or a mating plug.The new pouch young were removed 3-5 days postpartumto initiate the second cycle and bromocriptinewas given again to the adult females (25mg) (im).Blood samples (5m1) were collected from the lateral tailvein at specific times throughout pregnancy from 4levonorgestrel and 4 control implanted tammars.Plasma progesterone was measured using aradioimmunoassay validated for the tammar.Levonorgestrel implants were removed from anadditional 6 tammar wallabies one-month after theinitial implantation during the seasonal quiescenceperiod, reproduction in these animals was monitored forthe subsequent 9 months.RESULTSEleven of the twelve control implanted tammars gavebirth at the end of the frrst cycle and eight of theseanimals gave birth at the end of the second cycle (table1).~ 20e~~ 15e c-o~ 10Il..50Table 1: Birth in the tammar after treatment withcontrol or levonorgestrel implant.Control Levonorgestrel1 st Cycle 11/12 9/112 nd Cycle 8/11 0/8Nine of the twelve levonorgestrel treated animals gavebirth during the first pregnancy cycle, but none gavebirth at the end ofthe second pregnancy cycle (table 1).Birth was observed in 4 out of the 6 tammars that hadlevonorgestrel implants removed at the beginning of thebreeding season.Radioimmunoassay of progesterone showed nosignificant difference in circulating levels duringpregnancy for both control and experimental tammars(fig. 1).o--- Control-+-Levonorgestret5 10 15 20 25Days since pouch young removal30Fig 1: Plasma progesterone levels throughoutpregnancy in one control and one levonorgestrel treatedtammar.DISCUSSIONLevonorgestrel does not interfere with a pregnancyfollowing diapause in the tammar. Normal progesteronelevels were observed throughout pregnancy inlevonorgestrel treated animals. Levonorgestrelsuccessfully inhibits conception at the post-partumoestrus in the tammar wallaby. The lack of a postpartummating at the end of the frrst cycle inexperimental tammars suggests that levonorgestrel issuppressing ovulation, but this is still to be confirmed.The contraceptive effects of levonorgestrel arereversible in the tammar upon implant removal.Levonorgestrel could provide an alternative method forpopulation control of other macropodid marsupials, likethe eastern grey kangaroo, Macropus giganteus, insmall, selected wildlife parks and sanctuaries.116 117