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PubMed1988

Termination of the breeding season in the Suffolk ewe: involvement of an endogenous rhythm of reproduction.

Two studies were performed to determine if the transition into anestrus in the Suffolk ewe results from the lack of a decrease in photoperiod, a signal suggested to be important in maintaining the breeding season, or from an obligatory turn-off that reflects the expression of an endogenous rhythm of reproduction. Shortly after the autumnal equinox, three groups of ovariectomized ewes bearing s.c. Silastic implants of estradiol were placed in different lighting environments. A control group was exposed to normal variations in day length until the winter solstice and held on that day length thereafter. The two experimental groups experienced either a continuously decreasing day length or a continuously increasing duration of elevated melatonin levels during each 24-h period until mid-March. Reproductive activity, assessed by circulating levels of luteinizing hormone (LH), was marginally extended (2-3 wk) in the experimental groups. In a second experiment, two groups of ovary-intact ewes were exposed to photoperiodic treatments shortly after the winter solstice. A control group was held on the winter solstice day length (10L:14D) until the end of the study in mid-March. The experimental group experienced a 3-h photoperiodic reduction to 7L:17D. It remained to determine if that abrupt decrease could maintain reproductive induction. Again, the cessation of reproductive induction was marginally delayed in the experimental group (2-3 wk). This marginal delay in the arrest of reproductive activity seen in both experiments indicates that the lack of decrease in day length around and after the winter solstice may play some role in timing the end of the breeding season. However, our inability to prevent or markedly delay the termination of reproductive activity leads to the conclusion that the primary reason for the transition into anestrus is an obligatory turn-off. This obligatory process may be the expression of an underlying endogenous rhythm of reproduction.

Animals↗
PubMed1981

Decreased reproductive potential and reduced feed consumption in mature white leghorn males fed aflatoxin.

A pair-feeding study was conducted to investigate the relative importance of ingestion of aflatoxin (20 microgram/g diet) versus decreased feed consumption in explaining the effects of dietary aflatoxin on reproduction. Fifty-eight mature White Leghorn males were divided among three groups - control, 0 microgram/g diet ad lib; aflatoxin, 20 micrograms/g diet ad lib; and pair-fed, 0 microgram/g diet pair fed to 20 micrograms/g group. Aflatoxin and pair-fed males consumed significantly less feed than controls during weeks 1 through 5 of the 8-week aflatoxin feeding period. Measures of reproductive potential (semen volume, testes weights, spermatocrit, and plasma testosterone) for pair-fed males were not significantly different from males fed aflatoxin, although both groups were significantly lower than control males. Measures of aflatoxicosis (liver weight, liver fat, and plasma albumin) for pair-fed males were not significantly different from control males, although both groups were significantly different from males fed aflatoxin. In conclusion, decreased feed consumption did not produce symptoms of aflatoxicosis but accounted for 60% of the effects of aflatoxin on reproduction. Therefore, aflatoxin has nutritional and toxicological effects on reproduction.U

Aflatoxins↗
PubMedDate not supplied

[Blood levels of testosterone and its urinary excretion in women of reproductive age both neurosis-free during the climacteric period and with climacteric neuroses].

Blood testosterone content was studied by the radioimmunological method in 12 healthy women (5 of reproductive age, and 7 with climacteric age changes) and in 4 patients at the postmenopause suffering from climateric neurosis. Urinary excretion of testosterone glucuronide was studied by means of fluorometry in 11 healthy women (4 of reproductive age, and 7 at the climacteric) and in 6 patients at the postmenopause with climacteric neurosis. Healthy women of reproductive age displayed marked individual variations in the blood testosterone content both during the folliculin and the lutein cycle phases. The indices of urinary testosterone excretion varied in this group lees. As to healthy women with age climacteric changes and a regular cycle and those during the postmenopause--they showed marked variations both in blood testosterone content and in urinary testosterone excretion. There were no significant differences in the indices studied in healthy women of reproductive age and in healthy women with age climacteric changes. But in 8 of 11 women with climacteric neurosis blood testosterone content and urinary testosterone excretion were much greater than the upper borders of its variations in healthy women.

Adult↗
PubMed2005

Characterizing the symmetric equilibrium of multi-strain host-pathogen systems in the presence of cross immunity.

We investigate the population dynamics of host-pathogen systems in which the pathogen has a potentially arbitrary number of antigenically distinct strains interacting via cross-immunity. The interior equilibrium configuration of the symmetric multiple strain SIR model with cross-immunity is characterized. We develop an efficient iterative method for numerically solving the equilibrium equation together with a number of informative analytical approximations to the full solution. Equilibrium properties are studied as a function of the number of strains, reproduction number, infectious period, and cross immunity profile. We establish that the prevalence in the system increases monotonically with the number of strains and the reduction in cross immunity. Moreover, we demonstrate the existence of a phase transition separating high prevalence and low prevalence parameter regions, with the critical point being defined by sigmaR0 congruent with1, where sigma is the level of cross-immunity and R0 is the reproduction number. Above the threshold, prevalence saturates with increasing numbers of strains as a result of the inclusion of prohibition of co-infection in the model. Below the threshold, prevalence saturates much more rapidly as the number of strains increases--indicating that when cross-protection is sufficiently intense, the selective advantage for a pathogen to increase its diversity is substantially less than in the threshold region. Similarly, there is limited benefit to increased transmissibility (or decreased cross-immunity) both for the high and low diversity pathogen systems compared with systems at the threshold sigmaR0 congruent with1 where small increase in transmissibility can result in significant increase in prevalence.

Animals↗
PubMed1997

General overview of PRRSV: a perspective from the United States.

Four years after the report of its discovery, porcine reproductive and respiratory syndrome virus (PRRSV) continues to challenge swine producers, veterinary practitioners, and animal health researchers in the United States. The prevalence of infection is high--60% to 80% of herds is a reasonable estimate--but the clinical effects of infection vary widely among farms. In many herds, infection is unapparent and productivity seemingly unaffected. Some infected herds report occasional respiratory disease outbreaks in young pigs, or periodic outbreaks of reproductive disease, and a few herds experience severe, chronic disease problems, particularly in young pigs. In these herds, secondary infections with viral or bacterial pathogens, particularly Salmonella choleraesuis, Streptococcus suis, or Haemophilus parasuis typically occur concurrently with PRRSV infections. Understanding why some herds undergo devastating episodes of clinical disease and others show no apparent effects is central to solving the problem of clinical PRRS for swine producers. Understanding the ecology and epidemiology of PRRSV is the key to preventing and controlling PRRSV in the future. The objective of this article is to review recent developments in these areas.

Abortion, Veterinary↗
PubMed2002

Reduced body mass, food intake, and testis size in response to short photoperiod in adult F344 rats.

BACKGROUND: Although laboratory rats are often considered classic nonseasonal breeders, peripubertal rats of two inbred strains, F344 and BN, have both reproductive and nonreproductive responses to short photoperiods. Unmanipulated adult rats have not been reported to have robust responses to short photoperiod alone, although several treatments can induce photoperiodic responses in adults. In this study, we tested the hypotheses that unmanipulated F344 rats retain responses to short photoperiod as adults and that they have the necessary elements for an endogenous circannual rhythm of sensitivity to short photoperiod. RESULTS: Relative to rats kept in long photoperiods (L16:D8), adult F344 rats transferred at 4.5 months of age to short photoperiods (L8:D16) had significantly lower testis size, food intake, and body weight. In a second experiment, newly weaned F344 rats underwent an initial period of inhibition of reproductive maturation, lower food intake, and lower body weight in short photoperiod or intermediate photoperiod (L12:D12) relative to rats in long photoperiod. By 18 weeks of treatment, rats in the two inhibitory photoperiods no longer differed from long photoperiod controls. In short photoperiod, rats underwent a second period of slight reproductive inhibition between weeks 35 and 48, but there was an effect on body weight and slight inhibition of food intake only in an intermediate photoperiod. CONCLUSION: Male F344 rats retain photoresponsiveness as adults, with less reproductive inhibition but equivalent nonreproductive responses. There was only weak evidence for an endogenous timer controlling a circannual cycle of sensitivity to short photoperiod.

Aging↗
PubMedDate not supplied

Fetal testosterone insufficiency and abnormal proliferation of Leydig cells and gonocytes in rats exposed to di(n-butyl) phthalate.

Adult male rats previously exposed on gestation days (GD) 12-21 to di(n-butyl) phthalate (DBP) have reproductive tract malformations, particularly agenesis of the epididymis, decreased sperm production, and Leydig cell hyperplasia and adenomas. Although similar effects are produced by the potent androgen receptor (AR) antagonist flutamide and are indicative of disruption of male sexual differentiation via an antiandrogenic mechanism, DBP is not an AR antagonist. The purpose of the study was to determine whether DBP causes pathologic changes and alterations in androgen status in the testis during the prenatal period of male reproductive tract differentiation. Pregnant CD rats were given corn oil, DBP (500 mg/kg/day), or flutamide (100 mg/kg/day) p.o. on GD 12-21. At GD 16-21, DBP caused hyperplasia of Leydig cells, many of which were 3beta-hydroxysteroid dehydrogenase- and/or AR-positive. Focal areas of hyperplasia had increased numbers of Leydig cells positive for proliferating cell nuclear antigen (PCNA). At GD 21, testis atrophy was apparent, seminiferous cords in DBP-exposed fetuses were enlarged and contained multinucleated gonocytes that, unlike controls, were PCNA-positive. DBP, but not flutamide, markedly decreased testicular testosterone levels at GD 18 and 21. Fewer epididymal ducts and reduced AR staining in some ducts were evident with DBP treatment, whereas decreased overall AR staining was seen with flutamide in the presence of mild Leydig cell hyperplasia. Leydig cell proliferation is likely a compensatory mechanism to increase testicular steroidogenesis triggered by testosterone insufficiency. The overall decrease in androgen concentration is not corrected and results in reproductive tract malformations. The multinuclearity and proliferation of gonocytes suggests an underlying Sertoli cell dysfunction.

Abnormalities, Drug-Induced↗
PubMed2000

Year-class differences in the reproductive system, plasma prolactin and corticosterone concentrations, and onset of prebasic molt in male dark-eyed juncos (Junco hyemalis) during the breeding period.

Year-class differences in reproductive function were investigated in a free-living population of adult male Dark-eyed Juncos, Junco hyemalis, breeding in interior Alaska. Second-year males (SY, entering their first breeding season) were compared with after-second-year males (ASY, entering at least their second breeding season). We measured body mass, size of the cloacal protuberance (CP), testis mass, onset of prebasic molt, and concentrations of plasma luteinizing hormone (LH), testosterone (T), corticosterone (CORT), and prolactin (PRL) throughout the reproductive season (April to mid-July). There were no differences in SY and ASY body weights but SY males had smaller CPs and testis masses than ASY males during gonadal recrudescence and at the end of the breeding season. Plasma LH was elevated from April until mid-June and then decreased in the same way in both year classes. In contrast, plasma T was high from April until mid-May and was lower in SY than in ASY juncos shortly after they arrived on their breeding grounds at the end of April, but not at other times. In July, SY males started to molt earlier, suggesting that they became photorefractory earlier than ASY males. Plasma PRL increased progressively in both year classes between April and early June and decreased in early July. At this time, plasma PRL decreased earlier in SY than in ASY males. Plasma CORT changed seasonally, but did not differ between SY and ASY juncos. Thus, year-class differences in CP sizes and testis mass apparently did not result from SY males secreting less LH or more PRL or CORT than ASY males. It is suggested that differences in reproductive condition in SY and ASY juncos are mediated by interactions with conspecific birds and do not result from an intrinsic effect of age.

Animals↗
PubMed2001

Biological timing and the clock metaphor: oscillatory and hourglass mechanisms.

Living organisms have developed a multitude of timing mechanisms--"biological clocks." Their mechanisms are based on either oscillations (oscillatory clocks) or unidirectional processes (hourglass clocks). Oscillatory clocks comprise circatidal, circalunidian, circadian, circalunar, and circannual oscillations--which keep time with environmental periodicities--as well as ultradian oscillations, ovarian cycles, and oscillations in development and in the brain, which keep time with biological timescales. These clocks mainly determine time points at specific phases of their oscillations. Hourglass clocks are predominantly found in development and aging and also in the brain. They determine time intervals (duration). More complex timing systems combine oscillatory and hourglass mechanisms, such as the case for cell cycle, sleep initiation, or brain clocks, whereas others combine external and internal periodicities (photoperiodism, seasonal reproduction). A definition of a biological clock may be derived from its control of functions external to its own processes and its use in determining temporal order (sequences of events) or durations. Biological and chemical oscillators are characterized by positive and negative feedback (or feedforward) mechanisms. During evolution, living organisms made use of the many existing oscillations for signal transmission, movement, and pump mechanisms, as well as for clocks. Some clocks, such as the circadian clock, that time with environmental periodicities are usually compensated (stabilized) against temperature, whereas other clocks, such as the cell cycle, that keep time with an organismic timescale are not compensated. This difference may be related to the predominance of negative feedback in the first class of clocks and a predominance of positive feedback (autocatalytic amplification) in the second class. The present knowledge of a compensated clock (the circadian oscillator) and an uncompensated clock (the cell cycle), as well as relevant models, are briefly re viewed. Hourglass clocks are based on linear or exponential unidirectional processes that trigger events mainly in the course of development and aging. An important hourglass mechanism within the aging process is the limitation of cell division capacity by the length of telomeres. The mechanism of this clock is briefly reviewed. In all clock mechanisms, thresholds at which "dependent variables" are triggered play an important role.

Aging↗
PubMed1998

The effect of dietary protein on reproduction in the mare. V. Endocrine changes and conception during the early post partum period.

Pregnant Anglo-Arab and Thoroughbred mares (n = 24) were divided randomly according to age and breed into 4 groups of 6 mares each from approximately 6 weeks before their expected foaling date. Diets received by the 4 groups varied in essential amino-acid and total protein contents. Serum progestagen, FSH and LH concentrations were determined from the day of parturition until foal heat and during the 1st oestrous cycle following foal heat. Serum progestagen, FSH and LH concentrations did not differ between the treatment groups. Progestagen concentrations were high (mean = 7.0: 5.2-16.4 ng/ml) at parturition but decreased rapidly within 48 h. As progestagen concentrations decreased LH concentrations increased from Days 3-6 post partum to reach maximum values at, or the day after ovulation. FSH concentrations declined 3-4 d after parturition and increased 2-3 d before ovulation at foal heat. The duration of elevated progestagen concentrations during the luteal phase of the subsequent oestrous cycle affected the interovulatory period. A 12-14 d FSH cyclical releasing pattern occurred. Season/photoperiod affected the resumption of normal oestrous cyclicity during the post partum period. The duration of the 1st oestrous cycle after foal heat in mares fed a low-quality protein diet showed a greater range (13-30 d) compared to mares fed a high-quality protein diet (18-26 d).

Animals↗
PubMedDate not supplied

[Care of reproductive health in adolescents].

Sexual behaviour in adolescent period is an important factor of reproductive health in later life. The scope of the study is to assess features of sexual behaviour in boys and girls aged 15-19 in Croatia. The study included 2466 schoolboys and 2858 schoolgirls in six towns in Croatia. According to obtained data sexual experience has been present in 49% of boys and 22% of girls. 60% of sexually active adolescents don't use any contraceptive means. Basic knowledge in human reproduction as well as in contraception is very poor in almost all examinees. Rate of induced abortion is much lower than in their peers in Western Europe as well as in the United States. The needs for an intensive health education programme of children and adolescents as well as the administration of an effective programme for the protection of their reproductive health have been stressed.

Adolescent↗
PubMed1995

Progesterone concentrations in serum, follicular fluid, and oviductal fluid of the golden hamster during the periovulatory period.

In vitro, progesterone induces capacitation, hyperactivated motility, and acrosome reactions in sperm, possibly acting through a non-genomic plasma membrane receptor, but neither progesterone functions nor concentration within the mammalian oviduct during the periovulatory period is well characterized. The objectives of this study were to determine the physiological concentrations of progesterone in serum, follicular fluid, and oviductal fluid of golden hamsters during the period of the reproductive cycle in which capacitation and fertilization occur. Fluids were collected from different groups of animals for each of four time points: the normal time for mating (5-6 h post-LH surge [post-LH]), early in capacitation (8-9 h post-LH), immediately preovulation (11-12 h post-LH), and after ovulation near the beginning of fertilization (14-15 h post-LH). Oviductal fluid was collected by 1-h cannulation followed by cardiac puncture for serum collection and follicle aspiration for follicular fluid. Within each time period, the three types of fluid differed significantly in progesterone concentration. Over time, concentrations of progesterone did not change in either serum (range: 5.64-12.85 ng/ml) or follicular fluid (range: 4.2-7.4 micrograms/ml), but the concentration of progesterone in oviductal fluid decreased from 175.06 ng/ml at the first period to 44.01 ng/ml at the fourth (p < 0.05), while the volume of oviductal secretions collected by the same sampling procedure increased from 1.6 to 2.9 microliters (p < 0.05). With this information concerning in vivo concentrations of progesterone during capacitation and fertilization, the physiological role of progesterone in sperm-egg interactions can be addressed.

Animals↗
PubMed1981

[The effect of the non-antibiotic growth stimulators, Carbadox and Cyadox, on reproduction in laboratory animals].

The effect of growth stimulators Carbadox and Cyadox was studied in laboratory rats and mice as exerted on their fertility, gravidity, embryo ontogenesis, and genetic efficacy of these drugs was also tested. In all tests one dose approaching the dose used in practice and multiple doses were administered. No antifertility effects were observed in either sex of rats, slight reduction in fertility was found in treated male mice. No teratogenic effect was observed, but both stimulators acted highly embryotoxically. Irrespective of the dose, genetic hazard occurred, influencing the first stages of spermatogenesis (spermatogony), and increasing the incidence ob abnormalities of spermatozoon heads after Carbadox treatment. In all tests Cyadox was less harmful than Carbadox. The results show that it is somewhat hazardous to use both growth stimulators in the period of animal reproduction.

Animals↗
PubMed1999

Hard work impinges on fitness: an experimental study with zebra finches.

In experiments in which brood size is manipulated, it is impossible to disentangle the effects of changes in intensity and duration of parental care on parental fitness from those of changes in the parental energy budget. To determine whether a change in parental energy budget affects the costs of reproduction, we assessed the effects of increased levels of hopping activity, independent of parental care, on later reproductive decisions in zebra finches, Taeniopygia guttata. We imposed two levels of workload on individual, nonbreeding birds. After the workload periods, the birds were allowed to breed in ad libitum conditions. Each bird went through three alternating periods of working followed by breeding. The birds were more active, but weighed less and ate less, during the high workload than during the low workload periods. Clutch sizes and brood sizes did not vary with the previous work level. However, after a period on the high workload, reproduction, on average, was started 6 days later than after a low workload period. Females gained weight just before egg laying, but this might have been a result of egg production. If so, the delay in reproduction did not simply reflect extra time needed to restore body mass after a period of increased activity. We conclude that the level of daily activity itself, or the resulting energy budget during the workload periods, delayed reproduction. We suggest that these observations on the effects of increased activity demonstrate a causal mechanism for reduced residual fitness of parents. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1990

On the reproductive activity of the female Onchocerca volvulus.

Onchocerca volvulus worms, extracted from nodules by collagenase digestion, stained with haematoxylin and cleared in glycerol, were unravelled for longitudinal examination and later embedded in brain blocks for study of serial transverse sections. A classification system for female worms is proposed, based on the reproductive status of 446 worms from Guatemala, 94 from Liberia and 125 from Mali. They were categorized into fecund, inseminated specimens; uninseminated, but potentially fertile specimens, shedding ova destined to degenerate; worms changing from the uninseminated to the inseminated state and vice versa, which were few in number; old worms, with degenerate ovaries, whose genital tracts were either empty or had disappeared; and moribund or dead worms, characterized by loss of turgor, collapse and degeneration, calcification, or invasion by polymorphic, basophilic cells. Potentially fertile worms shed oocytes continuously and, when they were inseminated, embryonic development ensured. No evidence was found of a periodic cycle of reproduction. Inseminated worms were found in nodules without a male worm, and uninseminated worms in nodules harbouring male worms. Measurements are recorded of portions of the female reproductive tract and of the length of uterus occupied by the various embryonic stages in fully fecund worms. A significant difference in the length of the body behind the first and second ovaries was observed as between worms from West African savanna (Mali) and forest (Liberia). Limited observations were also made on meiosis in the oocyte, penetration of the oocyte by sperm, formation of the ovum, syngamy and zygote formation.

Animals↗
PubMed2005

GABA(B1) knockout mice reveal alterations in prolactin levels, gonadotropic axis, and reproductive function.

gamma-Aminobutyric acid (GABA) has been implicated in the control of hypophyseal functions. We evaluated whether the constitutive loss of functional GABA(B) receptors in GABA(B1) knockout (GABA(B1)(-/-)) mice alters hormonal levels, under basal and stimulated conditions, and reproductive function. The serum hormone levels were measured by radioimmunoassay, the estrous cyclicity was evaluated by vaginal lavages, and the mating behavior was determined by the presence of vaginal plugs. A moderate hyperprolactinemic condition was observed, in which prolactin increase and thyroid-stimulating hormone decrease were similar between genotypes. Basal luteinizing hormone (LH), follicle-stimulating hormone, thyroid-stimulating hormone, and growth hormone levels were similar between genotypes in each sex. Analysis of the gonadotropin axis revealed no differences in puberty onset between female genotypes. In con trast, the estrous cyclicity was significantly disrupted in GABA(B1)(-/-) female mice, showing significantly extended periods in estrus and shortened periods in proestrus. Reproduction was significantly compromised in GABA(B1)(-/-) females, with a significantly lower proportion of mice (37.5%) getting pregnant during the first 30 days of mating as compared with wild-type controls (87.5%). Moreover, only 14% of vaginal plug positive GABA(B1)(-/-) females had successful pregnancies as compared with 75% in the controls. In addition, the postovariectomy LH rise was significantly advanced in GABA(B1)(-/-) mice, while the response to estradiol feedback was similar in both genotypes. In conclusion, our endocrine analysis of GABA(B1)(-/-) mice reveals that GABA(B) receptors are involved in the regulation of basal prolactin titers. Moreover, the hypothalamic-hypophyseal-ovarian axis is seriously disturbed, with alterations in cyclicity, postcastration LH increase, and fertility indexes. The molecular mechanism underlying these hormonal disturbances remains to be addressed.

Animals↗
PubMed1994

The 72-kilodalton protein of the male reproductive tract is differentially expressed and developmentally regulated during Wolffian duct differentiation of the fetal mouse.

Differentiation of the mammalian reproductive tract into the male phenotype is dependent on the presence of functional testes secreting testosterone during in utero development. Recently, we identified a protein fraction (72 kDa) from the developing reproductive tract of the fetal male mouse that is able to mimic the effect of testosterone in stabilizing the Wolffian duct in vitro, suggesting a role played by this protein in mediating the effect of testosterone during Wolffian duct differentiation. In the present study, we further evaluated the masculinizing role of this protein by determining the specific appearance of the 72-kDa protein in relation to reproductive tract differentiation. Using Western blot and immunohistochemical analysis, we demonstrate that the protein was expressed specifically in the male reproductive tract and not in male non-reproductive organs, namely, lung, liver, or kidney. Within the male reproductive tract, the Wolffian duct derivatives demonstrated a high level of expression of the protein, whereas the urogenital sinus produced only a low level of reaction to this antibody in Western analysis and no reaction in the histochemical analysis. There was a gradual rise in expression of the protein in the male reproductive tract during the critical period of Wolffian duct differentiation. The female reproductive tract produced only a trace immune reaction in Western analysis and no reaction in immunohistochemical analysis. Thus, the results support the hypothesis that the 72-kDa protein plays a role in Wolffian duct differentiation.

Animals↗