Post-partum Mating Research Articles

Reproduction of the Red-Bellied Pademelon Thylogale billardierii (Marsupialia)

'Thylogale billardierii, which is abundant in Tasmania, is a seasonal breeder with most births in the months April, May and June. Parturition is followed by mating, and the zygote so produced remains dormant until either sucking becomes intermittent near the end of pouch life or the young is lost. The mean length of the oestrous cycle was determined at 30.3 days, not significantly longer than the duration of gestation (30.2 days). Removal of pouch young results in the birth of a new young 28.7 days later. Removal of the corpus luteum results in oestrus 11 days later. Pouch life is 202 days, and vacation of the pouch by the young coincides precisely with parturition and post-partum mating. The young mature at about 14-15 months.

Effects of inhibiting prolactin secretion on the maintenance of embryonic diapause in the suckling rat.

Treatment of rats with bromocriptine between days 5 and 8 after the post-partum mating resulted in suppression of serum prolactin levels and caused luteal regression. Although this treatment led to embryonic resorption when suckling was prevented by removing litters soon after birth, the diapausing embryos of animals nursing a litter of eight pups were unaffected by the treatment. These results suggest that the high levels of prolactin and progesterone in the circulation during lactation are not responsible for maintenance of the diapausing state.

Early Embryonic Development and Ovarian Activity During Concurrent Pregnancy and Lactation in the Hopping-Mouse Notomys Alexis.

In the hopping-mouse, following a postpartum mating, embryos enter the uterus on about day 5. Implantation occurs on about day 7 if there are no suckling pups, but zona-free blastocysts may remain up to day 18 if from four to seven suckling pups are present. Implantation is eccentric and initially involves interdigitation of trophectoderm and uterine epithelial cells, followed by epithelial cell displacement. The orientation is antimesometrial and, during further development, the embryo invaginates into the yolk-sac cavity. In the ovary, corpora lutea develop during the first few days of pregnancy and then remain unchanged in size or cellular morphology until implantation, regardless of the length of its delay. Peripheral progesterone levels likewise show little change during the preimplantation period. After implantation, a similar number of corpora lutea are found but they increase progressively in size due to luteal cell hypertrophy. The cells show all the organelles typical of steroid hormone synthetic activity and there is a corresponding increase in blood progesterone levels at this time. Vesicular follicles are present throughout concurrent pregnancy and lactation and are larger after implantation. There is no evidence of spontaneous ovulation except at the time of parturition.

Breeding of a Captive Colony of Notomys fuscus Wood Jones (Rodentia : Muridae)

Reproductive data were obtained from a captive colony of N. fuscus over 10 years. Females had an oestrous cycle averaging 7.4 days, and a gestation period averaging 34.3 days. Only three possible instances of post-partum mating were recorded, but. some lactating females returned to oestrus 14-22 days after birth of their young. There was no evidence of delayed implantation due to lactation. Vaginal bleeding occurred in pregnant females 8-17 days before birth. Seventy-four litters were born, litter sizes ranging from one to five, average 2.7. No breeding season was evident. Both sexes were reproductively mature at 70 days old. Comparisons are made with other species of Notomys, and their generally low reproductive rate discussed.

The Reproductive Rate of the Hopping-Mouse Notomys Alexis and Its Ecological Significance.

In the male hopping-mouse, spermatozoa first appeared in seminiferous tubules on day 60 and were present in the epididymis a few days later; ventral prostates markedly increased in weight between days 56 and 60. Some females had large Graafian follicles, stimulated uteri and perforate vaginae on day 40; corpora lutea were first observed on day 44, but most females did not spontaneously ovulate until after day 54. Gestation in post-partum mated, non-suckling females lasted about 32 days, with implantation on day 7 or 8. When four or more young were suckling, gestation increased to 39 days (mean); implantation took place between days 11-13 and 14-17 when there were either three or four, or five, suckling young respectively. From one to three unfertilized oocytes surrounded by cumulus cells were found in the Fallopian tubes between days 7 and 17 in some pregnant females. Post partum, the most common ovulation rate and litter size was 4; 72% of these litters fully survived to weaning; 10-15% of litters were of five or six young and nearly half of these fully survived to weaning; in the natural environment litters were of four or five young. Without post-partum mating and without suckling young, females had ovulated spontaneously by days 9-11. Significantly fewer females suckling from four to six young had oocytes at this time, but the percentage had increased by days 15-18. This indicates a delay, but not prevention, of spontaneous ovulation during lactation. Field-caught females from the southern Northern Territory were reproductively inactive on three out of four occasions. The fourth time, when there had been > 50 mm of rain in the preceding few weeks, all adult females caught had corpora lutea and some were pregnant. Greatest ovarian inhibition coincided with high population density. When compared to data for small northern temperate-zone rodents, most of the above reproductive parameters do not indicate a high reproductive rate, but data for closely related, apparently non-cyclic, Australian species appear to be similar except for, possibly, age of puberty and spontaneous ovulation during lactation. The significance of these results to r-strategy in this species is discussed.

Reproduction in the Plain Rock-Wallaby, Petrogale penicillata inornata Gould, in Captivity, with Age Estimation of the Pouch Young

'Reproduction in the plain rock-wallaby was studied in captivity. The oestrous cycle ranged from 30.2 to 32.0 days and the gestation period from 30.0 to 32.0 days. A post-partum mating usually followed birth; the resultant quiescent embryo developed and was born 28-30 days after premature removal of pouch young. The pouch life of the young ranged from 189 to 227 days, males and females maturing sexually at approximately 590 and 540 days respectively. Tail and hind foot lengths were found to be useful indicators of age of young up to the end of pouch life.

Aspects of reproduction in the genus Notomys (Muridae).

Reproductive biology was studied in captive N. alexis, N. fuscus, N. mitchellii and N, cervinus. All were polyoestrous, the oestrous cycle averaging 7.0-8.0 days in N. alexis and N. mitchellii and 9.0 days in N. fuscus. In N. cervinus there was a considerable variation in length; this species may be easily stressed and less adaptable to captivity. Gestation in the non-lactating animal lasted 32, 34-37 and 38-43 days in N. alexis, N. mitchellii and N, cervinus respectively; all three had post-partum oestrus and mating. Lactation appeared to delay implantation in N, cervinus and probably in N. mitchellii, but not in N. alexis; it lasted 3-4 weeks, during which time the young clung tenaciously to the teats. Oestrus was not always suspended during lactation in N. alexis, and conception may take place during suckling in this species. Interspecific variations in this pattern of reproduction are discussed, and the information compared with data from other Australian Muridae.

Viability of the rat blastocyst following the oral administration of potassium perchlorate or potassium iodide to the mother.

occur just before the normal time of blastocyst implantation but their physiological significance in normal pregnancy is not known. Ifendometrial accumulation of iodide is prevented by the oral administration of perchlorate to the mother, pregnancy still proceeds normally (Brown-Grant, 1966a). When implantation is delayed by ovariectomy early in pregnancy followed by the administration of progesterone alone or by concurrent lactation, the changes in endometrial iodide concentration still occur but are not immediately followed by implantation (Brown-Grant, 1966b). The possible importance of a high endometrial iodide concentration for the ability of the blastocyst to survive a delay in implantation has been examined. The hypothesis that a high endometrial iodide concentration might, in fact, be detrimental to implantation and thus act as a mechanism for rejecting blastocysts ofsubnormal viability has also been tested. In the first experiment, adult Wistar rats late in their fourth or fifth preg¬ nancy were caged singly with males and the date of post-partum mating deter¬ mined by the finding of spermatozoa in the vaginal smear or a vaginal plug. On this day (Day 0 of pregnancy), the male was removed and the litter size reduced to nine and maintained at this number. The animals were given a 1-0% (w/v) solution of KC1, KC104 or KI or a 0-1% (w/v) solution of KI to drink and the daily fluid intake for each rat was determined and the salt intake as mg salt/rat/day calculated. On Day 9 or 10 of the post-partum preg¬ nancy, the litter was removed, weighed and killed and the thyroid glands dissected out, pooled and weighed. On Day 12 or 13, the mother was killed, the number of implantation sites noted and the weight of the sites determined. Thyroid and adrenal weights were also measured. As shown in Table 1, the administration of 1 % KC104 solution had no significant effect on blastocyst survival or the ability to implant following the removal of the litter. The only

Observations on the problem of delayed nidation in suckling mice.

In the course of other studies, observations were made on pregnancy and delayed nidation in suckling mice which seem to explain some differences in the findings of previous authors. The present investigations were carried out with mice of the NMRI strain and of a strain bred at the University Hospital of Basle, here called the B strain. The animals were kept under uniform conditions. Following a post-partum mating, Kirkham (1916) found that a fifth, and Enzmann, Saphir & Pincus (1932) that nearly half of such females subsequently became pregnant. Fauvet (1941), on the other hand, stated that in the rat pregnancies are difficult or nearly impossible to obtain from post-partum matings, though we have been unable to confirm this statement. Mantalenakis & Ketchel (1966) reported a pregnancy rate of 96 % for suckling mice of the Charles River Breeding Laboratories, North Wilmington, Mass., and W. J\l=o\chle(personal communication) found that in one of the best commercial breeding farms for laboratory animals in the U.S.A. the proportion was nearly 100%. In previous investigations (Bloch, 1948), 25 % of the mice suckling more than two young became pregnant following post-partum mating. These mice had been bought from local dealers and did not belong to a special strain. In the present investigations, we found 131 pregnancies following 165 post-partum matings (79%) in the NMRI strain and fifty-six pregnancies after sixty-five matings (86%) in the strain. These are two especially fertile strains. In our former material, of 1800 litters born, the mean number of young/litter was 6-3 (range 1 to

Mechanism of the inhibition of implantation in suckling mice.

SUMMARY The conditions under which implantation is delayed in mice mated at the post-partum oestrus have been investigated. The critical litter size for the effect was shown to lie between three and nine pups per female. Delay of implantation was dependent on the presence of the litter until at least day 3 and the length of the delay could be significantly shortened by temporary litter removal on days 2 and 4. A study of the effect of parity showed that delayed implantation after post-partum mating continued to occur until the 4th litter. The incidence and length of implantation delay were reduced after five or more litters. During suckling-induced delay of implantation the increase in uterine capillary permeability which occurs on day 4 of normal pregnancy was shown to be delayed to as late as day 14. The rate of development and time of entry into the uterus of zygotes was also retarded in comparison with normal pregnancy. This pattern resembled that seen after hypophysectomy on day 1 of normal pregnancy.

Specific milk proteins associated with resumption of development by the quiescent blastocyst of the lactating red kangaroo.

Summary. The milk of three lactating red kangaroos (Megaleia rufa, Desmarest) was sampled at regular intervals and the whey protein fraction of each sample was subjected to starch-gel electrophoresis. When the quiescent blastocyst resulting from post-partum mating resumed development, two new specific milk proteins appeared in the mammary secretion. It is suggested that anterior pituitary secretion is responsible for this phenomenon. It is suggested also that the appearance of these proteins in the milk may be useful for the diagnosis of resumed development by the quiescent blastocyst of the red kangaroo.

Reproduction in the Grey Kangaroo, Macropus canguru, in captivity

Observations were made on the grey kangaroo, housed in yards, initially at Adelaide, S.A., and later at Canberra, A.C.T., to provide basic information on reproduction and growth. This information was required for the interpretation of data obtained from concurrent field studies. Grey kangaroos are capable of breeding throughout the year but with increased frequency between the months of September and March, referred to as the "breeding season". Typical mating behaviour is described. Mating, which usually lasted about 50 min, was first used to indicate oestrus and ovulation, but it was later found possible to detect when ovulation had occurred from a characteristic vaginal smear which is described. During the "breeding season" the length of the oestrous cycle of the grey kangaroo in captivity varied from 32 to 55 days; a greater variation in length than in any other marsupial in which cyclic reproductive phenomena have been adequately described, Grey kangaroos from South Australia had gestation periods of 29-31 days; those from south-eastern New South Wales, 33-35 days; and those from mid-northern New South Wales, 38 days. The characteristic gestation period from each geographical strain of kangaroo was altered by from 9 % to 15 % if the females were mated with males of other strains. It is suggested that the genetic constitution of the embryo influences the period of intra-uterine development. Fertile post-partum mating with subsequent lactation-controlled delayed implantation of the type exhibited by other macropodids was not found in the grey kangaroo, and thus a new young was not produced after premature removal of the earlier young from the pouch, but if the removal took place during the "breeding season" then the female usually returned to oestrus within 13 days. Wild females, which had recently had fertile matings and with pouch young aged about 235 days, were collected at Mt. Hope, N.S.W., plus two others in a small sample at another site with pouch young aged 44 and 151 days, but it is not yet known whether the embryos complete development. If these are viable, their development must be slowed down during part of the following days, to ensure complete vacation of the pouch by the earlier occupant. Mating occurred in three domestic females with pouch young aged 82, 247, and 271 days, but further young were not produced from these matings. Because of the slow rate of development of the pouch young-a pouch life of 312 days compared with 240 days for the red kangaroo-and due to the restricted "breeding season", each sexually mature female grey kangaroo can produce and rear only one young each year. After leaving the pouch, each young may be suckled by its mother for at least another 6 months. * Division of Wildlife Research, CSIRO, Canberra. t Department of Zoology, University of Adelaide; present address: Mrs. J. Marsh, 2 Nicolle Ave., Hawthorndene, S.A.

Post-partum breeding in the guinea-pig.

Information relating to post-partum mating has been described in guinea-pigs kept in six small colonies containing variable numbers of the sexes running together continuously in floor pens of standard size. Litters were born on the floor and rearing was communal (Method 1). Three other like colonies were similarly maintained, except that the females in late pregnancy were separated from the male to avoid post-partum mating (Method 2). The conditions of farrowing and rearing were similar to those of Method 1. The data given by thirty-four sows of a closely recorded (stock) colony bred in units of six females and one boar, but in which every litter was born and reared under ‘cage’ conditions (Method 3), were used for comparative purposes only.Post-partum mating was considered to have occurred only when the interval between the births of any two consecutive litters of the same sow did not exceed 70 days. Of litters born under Method 1, 80% were conceived at post-partum oestrus; the mean gestation period was 68 days. The average inter-parturition interval of all sows breeding under Methods 1 and 2 was 74 and 118 days respectively. The optimal ratio of the sexes in a colony breeding by both methods was judged to be twelve females to one male.Litter size varied between 3·98 (Method 1) and 3·69 (Method 3) and by all three breeding methods, the proportion of young already dead or that died at birth was about 5%. Deaths were more common in summer months when litter size was maximal.The post-natal death-rate during the first 28 days of life among young reared communally (Methods 1 and 2) was 10% and was fivefold that observed in litters reared separately by their mothers (Method 3). This death-rate was highest during the winter months due to the difficulty of providing adequate amounts of fresh green vegetables.The annual output of young guinea-pigs from colonies bred under Method 1 was 62% greater than that from other colonies bred by Method 2. The more rapid sequence of littering did not affect the quality (body weight) of the young at birth or at weaning.Attention has been drawn to a possible deleterious effect of intensive breeding to the health of the females and their lessened resistance to infection. It has been suggested that, for this reason, the breeding life of the sows should be limited to 1 year.