Lactational Anoestrus Research Articles

The lactational anoestrus of the sow: the status of the anterior pituitary-ovarian system during lactation and after weaning.

SUMMARY The status of the anterior pituitary-ovarian system of the sow was examined during lactational anoestrus and after weaning up to the occurrence of the first oestrus after weaning. The ovaries and uteri were examined and the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) contents of the anterior pituitary glands were measured. Suppression of follicular growth and uterine development was apparent during lactation. This was relieved by weaning, when follicle size increased and oestrus and ovulation occurred within 6 days. A high level of pituitary FSH was found during lactation which was maintained after weaning until oestrus occurred, when the level fell. The level of LH was low during lactation, rose after weaning and fell when oestrus occurred. Ovariectomy of sows during lactation did not affect the growth of the young. While ovariectomy during the oestrous cycle produced the expected uterine atrophy, ovariectomy during lactation did not result in any further decline in uterine weight or length, suggesting that oestrogen secretion is at a very low level during late lactation. Pituitary LH content rose as a result of ovariectomy performed during the oestrous cycle but failed to do so as a result of ovariectomy performed during lactation, thus demonstrating inability of the lactating sow to increase LH synthesis under circumstances when the cycling sow is capable of doing so. From these results it is postulated that (a) a considerable release of both FSH and LH occurs at about the time of the after-weaning oestrus, similar to that which is believed to occur at cyclic oestrus, (b) failure primarily of release of FSH and of synthesis of LH occurs during lactation which accounts for suppression of follicle growth, anoestrus and anovulation during lactation in the sow.

Anoestrus in the red kangaroo Megaleia rufa (Desmarest).

The red kangaroo, M. rufa, normally has a post-partum oestrus and a quiescent period of lactation as do some other macropod marsupials. The term "quiescent period of lactation" has been defined in this paper as the period of reproductive stasis between post-partum oestrus and the resumption of ovarian activity which follows when the female ceases, or almost ceases to suckle the young. This term is introduced to replace the term "lactation anoestrus". It has been shown that some females failed to undergo post-partum oestrus during prolonged drought, each female having entered anoestrus during the previous pregnancy; such pregnancies were not interrupted, but carried to term, and the young sometimes suckled for 3-4 months. In some other females, anoestrus set in during an unfertilized oestrous cycle. It is thought that anoestrus may result from lack of food because anoestrous females are found only during prolonged drought. The histology of the uteri of lactating anoestrous females has been described, and shown to be indistinguishable from that of the uteri of non-lactating anoestrous females, and very different from that in animals in the quiescent period of lactation. The anoestrous condition appeared in the uterus after the cessation of the luteal phase. Pregnancy is therefore independent of the oestrous cycle in Megaleia when the luteal phase has passed. The onset of anoestrus in Megaleia is compared with that in Elephantulus rupestris jamesoni Chubb, Sorex araneus (L.), Oryctolagus cuniculus (L.), Setonix brachyurus (Quoy & Gaimard), and Potorous tridactjhs (Kerr), all of which usually undergo post-partum oestrus. In Oryctolagus and Elephantulus, anoestrus may lead to the death respectively of the young and foetus. It is suggested that the milder consequences of anoestrus in Megaleia may be of adaptive significance to the species in a semi-arid environment, since the embryos and pouch-young of anoestrous females have a chance to survive drought.

REPRODUCTION IN THE FEMALE HYRAX (DENDROHYRAX ARBOREA RUWENZORII)*

An investigation carried out on 58 female hyraxes from a collection (sex ratio 57·04±4·26 per cent) made in the Ruwenzori region of Uganda. The juvenile ovary is bean‐shaped and exhibits no sub‐surface crypts; the mature ovary is deeply lobed. Ovaries of all animals contain prominent interstitial tissue and very many follicles at all stages of development up to antrum formation. There is a high incidence of follicular atresia. The antrum appears when the follicle is 0·47 mm in diameter, and the size of the follicle immediately prior to rupture is 1·7 mm. From the initiation of antrum formation, the theca interna of all normal follicles is hypertrophied.The fully formed corpus luteum averages 1·6 mm in diameter, but if pregnancy follows, it grows on to 2·1 mm. It maintains this size and an appearance of activity throughout pregnancy. All corpora lutea are formed by ovulation, the average number being 1·49. There are no accessory corpora lutea, and all luteal tissue is derived exclusively from the thecae internae of ruptured follicles. Old corpora lutea are readily identifiable histologically and probably persist throughout life.One or two young are born at a time, and parturition is followed by a lactation anoestrus which is probably terminated by an infertile ovulation.The left ovary ovulates more frequently than the right, and there is evidence of intrauterine migration of ova. Prenatal mortality, calculated from fifteen animals is 9·5 per cent. There is some evidence of strains of potentially higher and lower fecundity in the population.There appears to be no definite breeding season, but there are probably more births in mid‐year than at other times.The structure of the bicornuate uterus is described, and the significance of the mode of formation of the corpus luteum discussed.

Sex behaviour of purebred and crossbred merino and blackhead Persian ewes.

Summary. Data are presented on a number of aspects of the sex behaviour of four breeds of sheep in South Africa. In crossbred Dorset Horn : Persian ewes, puberty was reached at an average age of 399.7 days. Autumn-born lambs, however, showed their first signs of oestrus 67.2 days later than those born in winter. Ewes generally exhibited a seasonal pattern in their sex activity with a peak in autumn and the lowest level in spring. This was most pronounced in the Merino and least so in Blackhead Persians. Crossbred ewes by Dorset Horn sires occupied an intermediate position. The mean length of the oestrous cycle was 16.9 days, oestrus lasting 29.2 hr. Significant differences between breeds were found for the duration of oestrus, the period being shorter in purebred than in crossbred ewes. Dorset Horn : Persian lambs were born after a gestation period of 146.5 days. It was also observed that the males were being carried slightly longer than the female lambs. A period of lactation anoestrus was observed in all the breeds, but in crossbred Dorset Horn : Merino and Dorset Horn : Persian ewes, oestrus was first recorded at respectively 42 and 51 days post partum, as compared with 90.1 days for purebred Blackhead Persians and 103.3 days in the case of Merino ewes.

The reproduction of the African elephant, Loxodonta Africana

Between December 1946 and December 1948, and January to March 1950, 150 elephants made available in the course of control work carried out by the Uganda Game Department were examined in greater or less detail according to circumstances. Eighty-one were females, of which sixty-seven were adult and thirty-one had an embryo in the uterus. All the dissections were carried out in the field, and the present account includes observations on the terrain, the food of the elephant, and other aspects of its ecology. Linear measurements of the carcasses and photographs of the molar teeth provide a guide to the age of specimens. Tusk growth is nearly similar in males and females until puberty, after which those of females generally cease to grow. The reproductive organs of the male are briefly described; those of the female are described in more detail, and discrepancies between existing accounts are considered in the light of this relatively extensive series of specimens. The mode of formation of the ovarial sac is unusual and is described from foetal, neonatal and adult specimens. There is marked hypertrophy of the interstitial tissue of the foetal gonads during the later stages of gestation. Breeding occurs at all times of year, but mating is possibly more frequent in the period December to March than at other times. Both sexes reach maturity at 8 to 12 years, and the female continues to breed until old age. Parturition is followed by a lactation anoestrus, after which the female undergoes a number of brief oestrous cycles until pregnancy ensues, lactation being continued throughout the subsequent gestation period. The interval between parturition and subsequent conception is normally of the same order of duration as the gestation period, and the normal calving interval appears to be rather less than four years. The ovarian cycle of the adult is characterized by the occurrence of multiple ovulation and the presence of many apparently active and histologically indistinguishable corpora lutea in both ovaries at all the stages of pregnancy which were encountered. It is probable that the corpus luteum of pregnancy develops from one of a number of follicles which ovulate under the same hormonal stimulus, and that it persists together with the accessory corpora lutea, some of which arise from follicles which ovulate and some from follicles which luteinize without ovulating. The corpora lutea are replaced about mid-pregnancy by a second set, which are formed by the luteinization of all the follicles with antra in both ovaries; some at least of the larger ones ovulate while many smaller ones do not. Follicular growth is suppressed in the later stages of pregnancy. The cycle of events bears some resemblance to that which occurs in the mare, and the comparison is discussed in detail. The ovarian periphery is characterized by numerous subsurface crypts and papillose projections which increase the area of the germinal epithelium. A description of the placenta and foetal membranes is in preparation, and preliminary study reveals a striking similarity to Hyrax , particularly in the quadri-lobulate allantois. The findings are discussed with reference to the phylogenetic position of the genus, the probable role of the corpus luteum in pregnancy, and the significance of the results in relation to the conservation of existing wild elephant populations.

Studies on the breeding season and reproduction of the ewe Part III. The breeding season and artificial light Part IV. Studies on the reproduction of the ewe Part V. Mating behaviour and pregnancy diagnosis

During the course of three breeding seasons, daily observations of oestrus were undertaken on the following groups of ewes, all of which were running with ochred rams. One hundred and twenty ewes (pure bred and first-cross) of different breeds and ages, running with vasectomized rams under natural conditions. Twenty-eight grade Suffolk ewes fed on a submaintenance diet. Eighteen grade Suffolk ewes running with a fertile ram. Twenty ewes of several breeds exposed to artificial light.The effects of heredity (breed and individual), environment (season, year and nutrition), age and artificial light on the breeding season and related phenomena have been investigated. The results and conclusions were as follows:1. (a) There are breed differences in the extent of the breeding season, cycle length, incidence of silent heat and duration of heat (Table 29). (b) The duration of the breeding season is related to the geographical origin (latitude and altitude) of the breed, (c) The duration of the breeding season of the first-cross is intermediate between that of the two parents, (d) Individual differences in the number of oestrous cycles per ewe per season were more marked in the mountain breeds.2. (a) Of the ewe lambs, 79% exhibited oestrus during the shortest days only of the first breeding season. Their breeding season is not spread evenly about the shortest day as it is with adults. (b) The occurrence and length of the breeding season in ewe lambs is associated with early birth dates or with higher growth rates.3. (a) Significant differences exist between breeds in the age at first oestrus. (b) Ewe lambs born early in the season showed their first oestrus at later age and heavier weight than those born late.4. Annual differences in the duration of the breeding season, cycle length, incidence of silent heat and occurrence of first oestrus were negligible.5. (a) Submaintenance diet had no effect on the onset of the breeding season, but it converted oestrus into silent heat. Conception occurred less frequently after periods of underfeeding. (b) At high latitudes nutrition has only a minor effect on the breeding season of the ewe.6. (a) A constant high ratio of artificial darkness (8 hr. light: 16 hr. darkness) hastened the onset of the breeding season some 57 and 27 days in the two experimental groups. (b) A constant high ratio of artificial light (16 hr. light: 8 hr. darkness) hastened the end of the breeding season some 104 days on an average (in one experimental group), (c) There were breed differences in the latency of initiation and of cessation of the induced breeding season, (d) In the induced breeding season cycles of ovulation preceded the first oestrus, (e) Two thresholds of pituitary activity are suggested, one for the onset of ovulation, and the other for the manifestation of oestrus.7. (a) A high frequency of cycles outside the normal range (14–19 days) was observed in the mountain breeds and in ewe lambs. (b) The shortest average cycle length coincided with the shortest days of the year.8. A high frequency of silent heats (during the breeding season) was observed in the mountain breeds, in ewe lambs and during the second half of the breeding season.9. Oestrus was of longer duration in adults and yearlings than in ewe lambs.10. (a) Post-partum heat occurred in 56% of Suffolk ewes with an average lactation anoestrus of 35 days. (b) There is a relationship between the early onset of the breeding season and the incidence of post-partum heat, (c) Conception post-partum is partly inhibited by lactation.11. Mating behaviour was observed in animals of several breeds and ages (three patterns were recorded for ewes and eight patterns for rams).12. Irregular columnar cells in the vaginal smear of the ewe characterized late pregnancy.In addition, the breeding season of wild and domestic sheep was reviewed in relation to the environment with special reference to the length of daylight.

Studies on the breeding season and reproduction of the ewe Part I. The breeding season in different environments Part II. The breeding season in one locality

A knowledge of the exact length of the breeding season for improved breeds under different environmental conditions in this country is lacking. Such knowledge is of importance so that the lambing season can be arranged according to farm conditions. Such knowledge, apart from providing the necessary background for the successful application of artificial insemination and administration of hormones, helps to explain certain problems of infertility. By selection it should be possible to build up strains, by extending the breeding season at one or both ends, so as to get lambing at any required time. As the results below show, crossbreeding and selection could lead to early sexual maturity, prolonged breeding season or restricted lactation anoestrus, which would undoubtedly increase the reproductive potentiality of the ewe.

Reproduction in the Water‐Vole, Arvicola amphibius Linn.

Summary.1. Reproduction in the water‐vole, Arvicola amphibius, is described from field material comprising 128 males and 95 females.2. The reproductive organs resemble those of the bank‐vole.3. The breeding season extends from the end of March to the latter half of September, but fecund males were caught in February.4. Animals born early in the year breed in the same season. The average number of corpora lutea of pregnancy was 6‐4 and of embryos in utero 5–7.5. Males are non‐fecund in winter, when the testes are very small; the testes of non‐fecund adults can be distinguished from those of immature animals by the condition of the tunica albuginea.6. The female has a poly‐cestrous cycle, and both non‐parous animals and parous animals at the beginning of their second year may undergo infertile cycles. (Estrus is accompanied by distension of the uterus with fluid as in the rat and mouse.7. There is a post‐partum oestrus, and several animals were found to be pregnant and lactating. Animals which fail to become pregnant at the postpartum oestrus enter upon a lactation anoestrus. This may be followed by another oestrus, but late in the season the animal passes from lactation anoestrus to winter anoestrus without ovulating again.8. The ovarian follicles reach about 700/J. in diameter at oestrus, but large follicles are also found at all stages of pregnancy. The corpora lutea reach their maximum size, about 1–7 mm. in diameter, fairly late in pregnancy.9. Cyclical changes in the Fallopian tubes and uterus are described.10. The mammary glands afford good evidence of the condition of the animal and make it possible to distinguish between the first pregnancy of the season and a subsequent pregnancy.The material described above was obtained in 1932‐35 as part of a general programme of work on the reproductive processes in British mammals, and was made available to me by Dr. A. S. Parkes, who suggested this work.