bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic Aspects of Reproduction in Sheep
Authors: Notter DR 
Published: July 2008

ContentsMaintenance of high levels of realized fertility (defined as the percentage of ewes that lamb) and appropriate levels of fecundity are critical for efficient sheep production. The optimal level of fecundity in most situations is well below the maximum attainable level and can be targeted by combining selection among and within breeds with use of an expanding array of single‐gene mutations affecting ovulation rate and litter size. The heritability of litter size is approximately 0.10, allowing changes of up to 2%/year from simple mass selection. Mutations in several genes associated with the transforming growth factor β superfamily (BMPRIB, GDF9 and sex‐linked BMP15) can increase ovulation rates by 0.7–1.5 ova in heterozygous ewes. However, ewes that are homozygous for BMP15 or GDF9 mutations are sterile, so use of these mutations requires carefully structured breeding programmes. Improvements in fertility may be critical for autumn lambing or programmes that aspire to lamb throughout the year. Selection to improve fertility in spring matings has been successful; selected adult ewes have lambing rates of 80–85% in October and early November. The selected ewes have a dramatically reduced seasonal anestrus, and many ewes continue to cycle during spring and summer. Major genes affecting seasonal breeding have not been identified in sheep. Polymorphisms in the melatonin receptor 1a gene appear to be associated with seasonal breeding in some, but not all breeds. However, functional genomic studies of genes associated with circadian and circannual rhythms have potential to reveal additional candidate genes involved in seasonal breeding.
Updates on Reproductive Physiology, Genital Diseases and Artificial Insemination in the Domestic Cat
Authors: Axnér E 
Published: July 2008

ContentsReproduction in the domestic cat is characterized by large individual variations in the female oestrous cycle and in male semen quality. The female cat reproduction is strongly influenced by season, and new data suggest that it is possible that season also affects male fertility. Repeated periods of oestrus and spontaneous ovulation may lead to degenerative endometrial changes causing infertility. For artificial insemination (AI), induction of ovulation is necessary in the absence of the mating stimuli. The large variation in the relationship between follicular growth and timing of expression of oestrus complicates, however, timing of ovulation induction. Stress may lead to progesterone secretion by the adrenal glands and possibly have a negative impact on early pregnancy. The large individual variation in semen quality makes fertility evaluation and feline semen conservation a challenge. For AI, the semen can be deposited in the cranial vagina, the uterus or in the uterine tubes. Intrauterine insemination results in higher pregnancy rates than intravaginal but is more complicated. Surgical intrauterine or intratubal insemination has resulted in the birth of kittens, but is an invasive procedure that is not allowed in all countries. Transcervical intrauterine insemination with frozen‐thawed semen has, however, recently resulted in the birth of kittens.
Reproduction of the Female Ferret (Mustela putorius furo)
Authors: Lindeberg H 
Published: July 2008

ContentsThe domestic ferret is a seasonally polyoestrous species. Females reach puberty at the age of 8–12 months. Females exhibit a constant oestrus between late March and early August if they are not bred. Increasing tumescence in the pink‐coloured vulva is a sign of pro‐oestrus. Oestrus can persist for up to 5 months, but once ovulation is induced, either pregnancy or pseudopregnancy ensues. Follicular development and atresia overlap in such a manner that there is a recent cohort of follicles available for ovulation whenever copulation might occur. Copulation may last from 15 min to 3 h, the average being 1 h. Ovulation is induced by pressure on the cervix associated with copulation. After sufficient LH release, the pre‐ovulatory follicles mature and an average of 12 oocytes (5–13) per female are ovulated 30–40 h after copulation into the ovarian bursa. The ferret oocytes are most capable of being fertilized up to 12 h after ovulation, i.e. 42–52 h after copulation. Ferret oocytes ovulate at the metaphase of the second meiotic division (MII) embedded in three layers of corona radiata cells. Embryos enter the uterus over a period of several days starting on day 5 after mating. Between days 12 and 13 after mating, the embryos have become implanted in the endometrium. Implantation in the ferret is central with rapid invasion of the uterine epithelium by the trophoblast over a broad area that eventually becomes a zonary band of endotheliochorial placenta. Gestation length is 41 days (39–42 days). The domestic ferret gives birth to an average of eight kits (1–18 kits), which weigh 6–12 g at birth.
Physiology of the Canine Anoestrus and Methods for Manipulation of Its Length
Authors: De Gier J. , Beijerink NJ , Kooistra HS , Okkens AC 
Published: July 2008

ContentsProgression from early to late anoestrus is characterized by the appearance of a larger number of gonadotrophin‐releasing hormone (GnRH) pulses with a higher amplitude, an increase in the sensitivity of the pituitary to GnRH, an increase in ovarian responsiveness to gonadotrophins, and an increase in basal plasma follicle‐stimulating hormone (FSH) concentration. A period of increased luteinizing hormone (LH) pulsatility has been observed shortly before the onset of pro‐oestrus. Apart from these changes in the hypothalamus‐pituitary‐ovary axis, the initiation of a new follicular phase in the bitch is also stimulated by dopaminergic influences other than the accompanying plasma prolactin decrease. Metergoline, a drug which in a low dosage lowers the plasma prolactin concentration via a serotonin‐antagonistic pathway, does not shorten the anoestrus; while bromocriptine, in a dosage insufficient to cause a decrease in the plasma prolactin concentration, does prematurely induce a follicular phase. These observations indicate that it is not the decrease in the plasma prolactin concentration, but another dopamine‐agonistic influence that plays a crucial role in the transition to a new follicular phase. The dopamine‐agonist induced oestrus is associated with a rapid rise in the basal plasma FSH concentration, similar to what is observed during the physiological late anoestrus. Administration of GnRH, eCG and oestrogens may also be used to induce oestrus but with variable results. Oestrus can be prevented surgically or medically, for which purpose progestagens are the most important drugs. The mechanism is still unclear, although it has been demonstrated that with continuing medroxyprogesterone acetate (MPA) treatment the FSH response to GnRH stimulation decreases and changes occur in the pulsatile release of the gonadotrophins. In general, LH pulses coincide with a FSH pulse, but during MPA treatment, LH pulses were observed while there was such a small increase in FSH that it was not recognized as significant FSH pulse.
Basic Aspects of the Control of GnRH and LH Secretions by Kisspeptin: Potential Applications for Better Control of Fertility in Females
Authors: Caraty A , Franceschini I 
Published: July 2008

ContentsThe neuronal control of fertility and sterility has been a subject of research for years. However, nowadays, in spite of considerable literature about GnRH during the last few decades, the precise cellular and molecular mechanisms whereby gonadal steroids and other peripheral signals converge in the brain to achieve the fine regulation of GnRH secretion remains partially unknown. In this scenario, a major breakthrough in our understanding of the neuronal signals governing reproduction took place in 2003 with the discovery of metastin/kisspeptin as a major player in the control of GnRH secretion. This molecule, first described as having a crucial role in triggering the onset of puberty, is involved in all phases of reproductive life and hence has attracted the interest of many reproductive neuroendocrinologists. Administered either centrally or peripherally, kisspeptin strongly induces the secretion of gonadotropin in many species, mainly through stimulation of GnRH secretion. Kisspeptin cells involved in the control of GnRH secretion are located in two regions of the brain: the preoptic area and the arcuate nucleus. Carrying oestradiol receptor alpha, kisspeptin cells of these regions appear to be the main integration centres for the expression of both the positive and negative feedback of steroid on GnRH secretion. More recently, this molecule has been shown to be able to synchronize preovulatory surges in cyclic ewes and cause ovulation in seasonally acyclic ewes. This review summarizes the most relevant aspects of the role of kisspeptin in GnRH/LH release and the potential application of this molecule in new strategies for controlling female fertility.
The Expanding Role of Recombinant Gonadotropins in Assisted Reproduction
Authors: Adams TE , Boime I 
Published: July 2008

ContentsUsing recombinant gonadotropins for assisted reproduction of domestic species is still in its infancy. Yet, the purity, potency and pathogen‐free nature of recombinant gonadotropins make them attractive alternatives to tissue‐derived gonadotropic agents. In this study, the authors summarize the work to date using recombinant gonadotropins to enhance the ‐ fertility of domestic animals and they discussed their recent studies examining the biopotency of single chain analogues of human gonadotropins. In these studies, single chain analogues of follicle stimulating hormone (Fcα), chorionic gonadotropin (CGβα) or a gonadotropin construct with dual activity (FcCGβα) were administered to sheep pre‐treated with antisera directed against GnRH. Ovulation was induced 3 days after analogue administration using hCG (1000 IU, iv). Although Fcα or CGβα alone induced only modest oestradiol production during the pre‐hCG period, serum concentrations of oestradiol were markedly increased (p < 0.05) 3 days after administration of FcCGβα or the Fcα + CGβα combination. Final ovarian weight was significantly increased (p < 0.05) in animals receiving Fcα, Fcα + CGβα or FcCGβα. Collectively, these observations demonstrate that the single chain analogues of the human gonadotropins are active in sheep.
Follicle Development in Mares
Authors: Donadeu FX , Pedersen HG 
Published: July 2008

ContentsThe mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or to regress) at any given stage of follicular wave development. Periodic development of follicular waves continuously occurs during most of post‐natal life in the mare and is influenced by factors such as stage of oestrous cycle, season, pregnancy, age, breed and individual so that different types of follicular waves (minor or major, ovulatory or anovulatory) and different levels of activity within waves may develop under different physiological conditions. Changes in gonadotropin levels and/or in the sensitivity of follicles to circulating gonadotropins seem to account largely for these physiological variations in follicle development.
Embryonic and Early Foetal Losses in Cattle and Other Ruminants
Authors: Diskin MG , Morris DG 
Published: July 2008

ContentsEmbryo survival is a major factor affecting production and economic efficiency in all systems of ruminant milk and meat production. For heifers, beef and moderate yielding dairy cows, does and camelids it appears that fertilization generally lies between 90% and 100%. In high‐producing dairy cows there is a less substantive body of literature, but it would appear that it is somewhat lower and perhaps more variable. In cattle, the major component of embryo loss occurs before day 16 following breeding with some evidence of greater losses before day 8 in high‐producing dairy cows. In cattle late embryo loss, while numerically much smaller than early embryo mortality loss, nevertheless, causes serious economic losses to producers because it is often too late to rebreed females when they repeat. In multiple ovulating small ruminants, the loss rate is positively related to ovulation rate. Systemic concentrations of progesterone, during both the cycle preceding and following insemination, affect embryo survival rate with evidence that too high or indeed too low a concentration being negatively associated with survival rate. Uterine expression of mRNA for progesterone receptor, oestradiol receptor and retinol‐binding protein appears to be sensitive to changes in peripheral concentrations of progesterone during the first week after artificial insemination. Energy balance and dry matter intake during 4 weeks after calving are critically important in determining conception rate when cows are inseminated at 70–100 days post‐calving. Concentrate supplementation of cows at pasture during the breeding period has minimal effects on conception rates though sudden reductions in dietary intake should be avoided. For all systems of milk production, more balanced breeding strategies with greater emphasis on fertility and feed intake and/or energy balance must be developed. There is sufficient genetic variability within the Holstein breed for fertility traits. Alternative dairy breeds such as the Jersey or Norwegian Red could also be utilized. Genomic technology will not only provide scientists with an improved understanding of the underlying biological processes involved in fertilization and the establishment of pregnancy, but also, in the future, identify genes responsible for improved embryo survival. Its incorporation into breeding objectives would increase the rate of genetic progress for embryo survival.
Epigenetic Programming of Porcine Endometrial Function and the Lactocrine Hypothesis
Authors: Bartol FF , Wiley AA , Bagnell CA 
Published: July 2008

ContentsEpigenetic programs controlling development of the female reproductive tract (FRT) are influenced by the effects of naturally occurring bioactive agents on patterns of gene expression in FRT tissues during organizationally critical periods of foetal and perinatal life. Aberrations in such important cellular and molecular events, as may occur with exposure to natural or manmade steroid or peptide receptor‐modulating agents, disrupt the developmental program and can change the developmental trajectory of FRT tissues, including the endometrium, with lasting consequences. In the pig, as in other mammals, maternal programming of FRT development begins pre‐natally and is completed post‐natally, when maternal effects on development can be communicated via signals transmitted in milk. Studies involving relaxin (RLX), a prototypic milk‐borne morphoregulatory factor (MbF), serve as the basis for ongoing efforts to identify maternal programming events that affect uterine and cervical tissues in the neonatal pig. Data support the lactocrine hypothesis for delivery of MbFs to neonates as a specific consequence of nursing. Components of a maternally driven lactocrine mechanism for RLX‐mediated signalling in neonatal FRT tissues, including evidence that milk‐borne RLX is delivered into the neonatal circulation where it can act on RLX receptor (RXFP1) ‐positive neonatal tissues to affect their development, are in place in the pig. The fact that all newborn mammals drink milk extends the timeframe of maternal influence on neonatal development across many species. Thus, lactocrine transmission of milk‐borne developmental signals is an element of the maternal epigenetic programming equation that deserves further study.
Sexual Maturation in the Bull
Authors: Rawlings N , Evans ACO , Chandolia RK , Bagu ET 
Published: July 2008

ContentsIn this review, we describe the process of sexual maturation in the bull calf. The testes of the bull grow relatively slowly until approximately 25 weeks of age and then a rapid phase of growth occurs until puberty, at 37–50 weeks of age. During the early postnatal phase of slower growth of the testis pre‐spermatogonia and some spermatogonia are established, adult Leydig cells appear and undifferentiated Sertoli cells are produced. The rapid testicular growth, after 25 weeks of age, consists of marked increases in the diameter and length of the seminiferous tubules, dramatic proliferation and differentiation of germ cells, with mature spermatozoa occurring between 32 and 40 weeks of age. The adult Leydig cell population is largely in place by 30 weeks of age and that of Sertoli cells by 30–40 weeks of age. Serum concentrations of LH increase from 4 to 5 weeks of age, to an early postnatal peak at 12–16 weeks of age, followed by a decline to 25 weeks of age. Serum FSH concentrations are high postnatally, declining to approximately 25 weeks of age. Serum testosterone concentrations increase during the phase of rapid testicular growth. Hypothalamic opioidergic inhibition may abate transiently to allow the early postnatal increase in LH secretion, while testicular androgenic negative feedback probably contributes to the decline in gonadotropin secretion to 25 weeks of age. Several lines of study have led us to suggest that early postnatal gonadotropin secretion is pivotal in initiating the process of sexual maturation in the bull calf.
Epigenetic Regulation of Foetal Development in Nuclear Transfer Animal Models
Authors: Dinnyes A , Tian XC , Yang X 
Published: July 2008

ContentsSomatic cell nuclear transfer (SCNT, ‘cloning’) holds great potential for agricultural applications, generation of medical model animals, transgenic farm animals or by ‘therapeutic cloning’ for generating human embryonic stem cells for the treatment of human diseases. However, the low survival rate of SCNT‐derived pregnancies represents a serious limitation of the current technology. In order to overcome this hurdle, a deeper understanding of the epigenetic reprogramming of the somatic cell nuclei and its effect on the pregnancy is needed. Here we review the literature on nuclear reprogramming by SCNT, including studies of gene expression, DNA methylation, chromatin remodelling, genomic imprinting and X chromosome inactivation. Reprogramming of genes expressed in the inner cell mass, from which the body of the foetus is formed, seems to be highly efficient. Defects in the extra‐embryonic tissues are probably the major cause of the low success rate of reproductive cloning. Methods to partially overcome such problems exist, yet more future research is needed to find practical and efficient methods to remedy this problem. Improvement of the survival of foetuses is a central issue for the future of agricultural SCNT not only for its economic viability, but also because in lack of improvements in animal welfare current regulations can block the use of the method in the EU and several other countries.
A Proposed Role for VEGF Isoforms in Sex‐Specific Vasculature Development in the Gonad
Authors: Bott RC , Clopton DT , Cupp AS 
Published: July 2008

ContentsMany scientists have expended efforts to determine what regulates development of an indifferent gonad into either a testis or ovary. Expression of Sry and upregulation of Sox9 are factors that initiate formation of the testis‐specific pathway to allow for both sex‐specific vasculature and seminiferous cord formation. Migration of mesonephric precursors of peritubular myoid cells and endothelial cells into the differentiating testis is a critical step in formation of both of these structures. Furthermore, these events appear to be initiated downstream from Sry expression. Sertoli cell secretion of growth factors acts to attract these mesonephric cells. One hypothesis is that a growth factor specific for these cell linages act in concert to coordinate migration of both peritubular and endothelial cells. A second hypothesis is that several growth factors stimulate migration and differentiation of mesonephric ‘stem‐like’ cells to result in migration and differentiation into several different cell lineages. While the specific mechanism is unclear, several growth factors have been implicated in the initiation of mesonephric cell migration. This review will focus on the proposed mechanisms of a growth factor, Vascular Endothelial Growth Factor, and how different angiogenic and inhibitory isoforms from this single gene may aid in development of testis‐specific vascular development.
Application and Commercialization of Flow Cytometrically Sex‐Sorted Semen
Authors: Rath D , Johnson LA 
Published: July 2008

ContentsThe current technology to sort X and Y chromosome bearing sperm population requires individual identification and selection of spermatozoa in a modified high‐speed flow cytometer. For farm animal species, the technology is capable of producing sexed sperm at greater than 90% purity. However, only in the bovine, the technology has reached a developmental level that allows its commercial application. Meanwhile, the demand for female calves has grown rapidly, which encourages the demand for sex‐sorted semen from high genetic value bulls. The success of the technology will depend mainly on the fertilizing capacity of the sorted spermatozoa, as this is the most affecting and economically relevant factor. To date, fertility is still variable and is quite dependant on post‐sort processing. New processing techniques are under investigation and will likely be able to improve the fertility rates after AI with sex‐sorted semen. It is of great importance to select the right bulls and to test the sorted samples on a routine basis. In addition to the demand for sex‐sorted semen by the cattle industry, there is also a significant demand expressed by pig farmers. However, it is still unknown if the use of sex‐sorted semen through commercial pig AI will be economically feasible. For the pig, the combination of in vitro fertilization with sexed semen and non‐surgical embryo transfer is an alternative that merits further scientific attention. Recent developments in ovine AI and ET will make it very likely that commercial sheep industry will adopt the sexing technology in their breeding concepts.
Low‐Dose Insemination in Pigs: Problems and Possibilities
Authors: Vazquez JM , Roca J , Gil MA , Cuello C , Parrilla I , Caballero I , Vazquez JL , Martínez EA 
Published: July 2008

ContentsLow‐dose AI procedures are required by the pig industry to efficiently utilize emerging sperm technologies, such as cryopreservation and sex‐sorting. Currently, several different procedures for inseminating with a low or very low number of spermatozoa have been described. Deep intrauterine insemination allows the deposition of the spermatozoa in the depth of the uterine horn, allowing a significant reduction in the number of spermatozoa inseminated with maintenance of optimal reproductive performance. Intra‐oviductal laparoscopic insemination has been recently applied in pigs. This technique has proved to be applicable with diluted and sex‐sorted spermatozoa. This review discusses several problems encountered during the development of deep intrauterine insemination and intra‐oviductal laparoscopic insemination of pigs and provides potential solutions for the practical application of both the technologies.