PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Reproductive Period”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74Linked to original sources
PubMed1996

Rank and reproduction in the female spotted hyaena.

Female reproductive success varies with social rank in many gregarious mammals, including primates, ungulates and carnivores. Social groups of spotted hyaenas (Crocuta crocuta) are structured by hierarchical dominance relationships that determine individuals' priority of access to food and other resources. The influence of female social rank on several measures of reproductive success was examined in a population of free-living Crocuta in Kenya. The study population was continuously observed for seven years, making it possible to document litter sizes, interbirth intervals, ages of cubs at weaning, intervals between weaning one litter and conceiving the next, annual rates of production of cubs, and survival of offspring to reproductive maturity. The relationship between availability of food, social rank, and female fertility was examined by monitoring abundance of prey throughout the study period. Most measures of reproductive performance were strongly influenced by social rank. High-ranking females began breeding a younger ages, were more frequently able to support pregnancy and lactation concurrently experienced shorter intervals between litters, and produced more surviving offspring than did lower-ranking females. Low-ranking females exhibited better reproductive performance when prey animals were abundant than when prey were relatively scarce. By contrast, reproductive performance among high-ranking females was always superior to that exhibited by low-ranking females, and did not vary with prey abundance. Fertility among high-ranking females thus appeared to be less vulnerable to fluctuations in the food supply than was that among low-ranking females.

Animals↗
PubMed1997

[The sociomedical and risk-insuring protection of women depending on their reproductive function].

The role and importance of accomplished fertility compared to the total number of pregnancies is discussed from the point of view of working activities, medico-social insurance and amount of risk insurance indemnities of women during different phases of the individual reproductive cycle for the period 1985-1995 in Bulgaria. It is pointed out that the continuing unfavourable demographic tendencies are directly linked with the level of the reproductive function of women. Their individual behaviour in the accomplishment of that function is motivated mainly by changes of economic factors, optimal social insurance indemnities during different phases of the cycle, success in the control of pregnancy complications and especially increasing emotional acceptance of abortions, which sharply exceed births.

Abortion, Legal↗
PubMed1981

Evidence for a photoperiod-sensitive pacemaker for estrous cycle of the rat.

To define how the periodicity of light regulates reproductive cyclicity in the rat, animals were exposed to slightly altered photoperiods in which the light/dark ratio was maintained as in the control (14L + 10D) environment. Exposure to a 22.5-h photoperiod (13.125L + 9.375D) for 10-80 days induced a significant prolongation of the first and all subsequent vaginal cycles by about 30 h. Ovulation in these animals was normal. By contrast, exposure to a 26-h photoperiod (15.167L + 10.833D) had no significant effect on vaginal cyclicity. A comparison of the data with theoreticaly generated results revealed that a significant prolongation of the estrous cycle under conditions of a shortened photoperiod cannot be accounted for by a simple entrainment of the estrous cycle to the timing of the new circadian rhythm. Rather, the evidence suggested that a photoperiod-entrained rhythm may interact with a second rhythm of different periodicity to alter the duration of the reproductive cycle as measured in this study.

Animals↗
PubMed2004

Sexual behavior, neuroendocrine, and neurochemical aspects in male rats exposed prenatally to stress.

The present study was designed to examine some short- and long-term effects of maternal restraint stress--during the period of sexual brain differentiation--on reproductive and endocrine systems, sexual behavior, and brain neurotransmitters in male rat descendants. Pregnant rats were exposed to restraint stress for 1 h/day from gestational days (GDs) 18 to 22. Prenatal stress did not influence the wet weight of sexual organs and the quantity of germ cells in adult male pups; however, these animals showed reduced testosterone levels, delayed latency to the first mount and first intromission, and also decreased number of ejaculations. Additionally, there was an increase in the dopamine and serotonin levels in the striatum. Our results indicate that prenatal stress had a long-term effect on neurotransmitter levels and sexual behavior. In this sense, reproductive problems caused by injuries during the fetal period can compromise the later success of mating as well as the capacity to generate descendants.

Adrenal Glands↗
PubMed2004

Patterns of cercarial production from Diplostomum spathaceum: terminal investment or bet hedging?

In the production of the infective cercariae of trematodes, the terminal investment hypothesis of life-history theory predicts that the rate of host exploitation and cercarial production should increase during the period of cercarial shedding since the reproductive value of the parasite decreases during this period. In contrast, a bet hedging hypothesis that focuses on the success of transmission when host contact rate is variable predicts that cercarial production should decrease in an attempt to keep the host alive for longer and thus would increase the probability of successful transmission. We examined these two hypotheses under laboratory conditions and recorded the production of Diplostomum spathaceum cercariae from naturally infected snail hosts, Lymnaea stagnalis. The average number of cercariae produced per day decreased as the snail host approached death counter to the terminal investment hypothesis. The finding supports the prediction of the bet hedging hypothesis and implies that the pattern of cercarial production may be explained by reduced virulence of the parasite within the snails to ensure extended total production time of cercariae. Nevertheless, survival of infected snails was still lower than uninfected snails suggesting that ultimately the infection still increased snail mortality rate. Cercarial production varied between days but was not cyclic, probably because of the physiology of the sporocysts within snails. Fewer cercariae were released at night, which may increase transmission efficiency to diurnally-active fish hosts. The mechanisms associated with daily cercarial production are discussed.

Animals↗
PubMed2026

The importance of integrating genetic testing into reproductive medicine: a retrospective observational study investigating the monogenic causes of human infertility in couples considering ICSI.

The genetic landscape of human infertility is complex with diverse etiologies. Identifying the underlying etiology is crucial for guiding reproductive decisions and improving management for infertile couples. Here, we aim to report on the molecular spectrum of monogenic genetic causes of reproductive failure. Over a 3-year period, we recruited all infertile couples considering assisted reproductive technologies (ART) for whom the underlying genetic cause had been identified, in either partner, using exome sequencing (ES). Clinical data of all participants along with their hormonal profiles, sonographic findings and spermograms were recorded. The study included 50 couples with primary infertility. Clinically, male factor infertility was documented in 26 patients, female factor infertility in 10, while reproductive failure was unexplained in the remaining 14 couples. All participating couples had potentially disease-causing variants in infertility genes. ES identified variants related to male infertility in 26 men, while variants in female infertility-related genes were detected in the remaining couples (n = 24). According to ACMG classification criteria, 78% (39/50) of couples harbored pathogenic/likely pathogenic (P/LP) variants, whereas 22% (11/50) carried variants of uncertain significance (VUS). In view of the identified genetic etiologies, the cohort was stratified into two groups based on the predicted reproductive outcome: (1) couples with significantly impaired reproductive potential, and (2) couples who can have biological children using appropriate medical interventions. However, classifications involving VUS were interpreted cautiously and considered exploratory. This study provides further evidence for the molecular heterogeneity of human infertility and highlights the usefulness of genetic testing for infertile couples pursuing ARTs.

Humans↗
PubMed2004

Demography of soybean aphid (Homoptera: Aphididae) at summer temperatures.

Soybean aphid, Aphis glycines Matsumura, is now widely established in soybean, Glycine max L., production areas of the northern United States and southern Canada and is becoming an important economic pest. Temperature effect on soybean aphid fecundity and survivorship is not well understood. We determined the optimal temperature for soybean aphid growth and reproduction on soybean under controlled conditions. We constructed life tables for soybean aphid at 20, 25, 30, and 35 degrees C with a photoperiod of 16:8 (L:D) h. Population growth rates were greatest at 25 degrees C. As temperature increased, net fecundity, gross fecundity, generation time, and life expectancy decreased. The prereproductive period did not differ between 20 and 30 degrees C; however, at 30 degrees C aphids required more degree-days (base 8.6 degrees C) to develop. Nymphs exposed to 35 degrees C did not complete development, and all individuals died within 11 d. Reproductive periods were significantly different at all temperatures, with aphids reproducing longer and producing more progeny at 20 and 25 degrees C than at 30 or 35 degrees C. Using a modification of the nonlinear Logan model, we estimated upper and optimal developmental thresholds to be 34.9 and 27.8 degrees C, respectively. At 25 degrees C, aphid populations doubled in 1.5 d; at 20 and 30 degrees C, populations doubled in 1.9 d.

Animals↗
PubMed2006

Reproductive losses caused by bovine viral diarrhea virus and leptospirosis.

Bovine viral diarrhea virus and Leptospira spp. are two of the common pathogenic organisms responsible for reproductive losses in cattle worldwide. Both can be come endemic in herds resulting in chronic low-grade reproductive losses or they can be introduced into relatively naïve herds, resulting in substantial reproductive losses over a short period of time. Both organisms are a differential diagnoses for common reproductive losses that veterinarians investigate, including low conception rates and abortions.

Abortion, Veterinary↗
PubMed2004

A simulation exercise to teach principles of bovine reproductive management.

Students in Reproductive Management (a senior-level course with approximately 20 to 50 students per semester) at the University of Missouri-Columbia are required to participate in a simulation exercise that is designed to improve reproductive efficiency in a beef herd. During a simulated 5-yr period, students must 1) improve reproductive efficiency in a beef cow-herd through implementation of reproductive management principles; 2) determine the economic impact of reproductive management decisions in a beef herd; and 3) evaluate the constraints of different geographical locations on approaches to reproductive management. Groups of three to four students are provided with the reproductive and economic records of a farm/ranch located in different parts of North America. Students create reproductive management plans consisting of 1) detailed discussion of farm/ranch environment (climate, terrain, forage and grain availability, and stocking rate; season for breeding and calving; and justification for choice of breed); 2) assessment of current level of reproductive performance; 3) identification and economic justification of specific (measurable) objectives; 4) discussion of alternatives for accomplishing specific objectives; 5) prediction of reproductive performance (pregnancy rate, quantity of calf weaned per cow exposed, and cost per quantity of calf weaned) in response to implementation of specific management practices; and 6) an annual and 5-yr reproductive and economic summary. Students obtain livestock marketing information for their assigned location via the Internet. Spreadsheets were developed to calculate the reproductive efficiency of postpartum cows and replacement heifers based on management decisions made by the groups and to calculate a yearly economic summary for each of the 5 yr. Management decisions are justified in a written report, and oral presentations are given to the class when the project is completed. Greater than 85% of students indicated that the exercise increased their understanding of how management decisions affect reproductive efficiency and profitability in a beef operation and also provided added confidence for students that applied for beef management positions.

Animal Feed↗
PubMed1997

Oestrogens and psychological well-being.

The last decade has seen increased interest in the role of hormones, including oestrogens, not only in regulating growth, sexual development and reproduction but in maintaining a sense of psychological well-being. Episodes of change in oestrogen levels, whether increasing or decreasing, are high-risk periods for the emergence of psychological symptoms in some women. This may be due to a 'kindling effect' for women with previous psychological disturbance, an effect on circadian rhythm activity and therefore altered neurovegetative functions, or an effect on central rhythmic functioning between the hypothalamus and the cerebral cortex, all mediated by effects on neurotransmitter systems. Data supporting these hypotheses come from animal studies as well as converging research in several areas including the study of psychological side-effects of oral contraceptives, the study of mood and cognitive disturbances related to the menstrual cycle, the studies of states of hormonal change such as pregnancy and the menopause and, of course, studies of women with psychiatric disorders such as major depression, seasonal affective disorder and dementia. Improvement in such symptoms via hormonal therapies or other interventions will probably lead to better quality of life for women and may actually impede the deterioration associated with ageing and certain medical illnesses. Current data support a relationship between oestrogen and psychological well-being.

Cognition↗
PubMed2005

[Changes of biomass allocation of Artemisia frigida population in grazing-induced retrogressive communities].

The study showed that under the disturbance of grazing, the biomass of Artemisia frigida leaves, stems, roots and total plant were increased with increasing retrogressive degree, and that of roots was increased more. The biomass of inflorescences and fruits was increased in light retrogressive community while decreased rapidly in mid retrogressive community, and no reproductive model was observed in heavy retrogressive community. With the increase of retrogressive degree, biomass allocation changed. The allocation to roots increased, but that to sexual reproduction decreased, which was badly inhibited in heavy retrogressive community, accompanying with the change of reproduction pattern. As for the dynamics of resource allocation, the resource was prior to allocate to aboveground portion, especially to photosynthesis organ from early to mid growth period, and allocate to sexual reproduction or reserve organ from mid to late growth period, with the increase of retrogressive degree. The alternation of reproductive pattern was the key that A. frigida population resisted grazing and became the established species in heavy retrogressive community. The change pattern of resource allocation made the allocation harmonious between the growth, resistance and reproduction, and was the substantial base that A. frigida population became the constructive species in heavy retrogressive community.

Animal Husbandry↗
PubMed1991

Tropical photoperiods affect reproductive development in the musk shrew, Suncus murinus.

The purpose of the present studies was to determine whether reproductive development in male musk shrews (original stock from Guam Island, 13 degrees N latitude) could be altered by small, ecologically relevant changes in photoperiod. In the first experiment, effects of changes in photoperiod equivalent to those seen between the 2 solstices on Guam Island (90 min) on reproductive maturation were investigated. The results showed that a 90-min difference in photoperiod had a significant effect on weights of various androgen-sensitive target tissues. Furthermore, there was little evidence that the preweaning photoperiod had an effect on the response to the postweaning photoperiod. In the second experiment, effects of changes in photoperiod equivalent to those seen between the equinoxes and solstices on Guam Island (45 min) on reproductive maturation were investigated. The results showed that both a decrease and an increase in photoperiod by 45 min had a significant effect on weights of various androgen-sensitive target tissues. Overall, these results suggest that animals living close to the equator can potentially use small changes in day length to alter or time reproductive function.

Animals↗
PubMedDate not supplied

[Characteristics of the hypothalamo-hypophyseal regulation and morphological and functional state of the reproductive organs in female rats, androgenized in the neonatal period, depending on the time of the action of testosterone].

Testosterone propionate was injected to rats in a dose of 150 microng on the 2nd, 3rd and 4th day or in a dose of 500 microng on the 5th day after birth. Histological picture of the ovaries, vagina and uterus, the content of progesterone and its C20-restored metabolite in the ovaries, the LH-releasing activity of the hypothalamus, and the LH and FSH in the adenohypophysis were studied in these rats at the age of 3-5 months. The effects of the neonatal andronization of rats proved to depend on the time of testosterone action at all the levels of the hypothalamus-hypophysis-ovaries-accessory organs. Early administration of androgen caused more severe injuries of the reproductive system.

Animals↗