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New approaches to increasing oocyte yield from ruminants
- E. E. Telfer, R. Webb, R. M. Moor, R. G. Gosden
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- Journal:
- Animal Science / Volume 68 / Issue 2 / March 1999
- Published online by Cambridge University Press:
- 18 August 2016, pp. 285-298
- Print publication:
- March 1999
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Artificial insemination, superovulation and embryo transfer have had beneficial impacts on animal production but a limiting factor to realizing the full potential of these techniques and of other reproductive technologies is the availability of fertile oocytes. To overcome this problem, methods for maturing oocytes in vitro (IVM) have been developed. The production of bovine embryos by IVM is in commercial use but the rate of success and quality of embryos is low. The lack of success may be due to the quality of oocytes that are being matured and it would be preferable to utilize the abundant source of immature oocytes from preantral and primordial follicles by developing systems for in vitro growth (IVG). Several culture systems that utilize early growing follicles as a source of oocytes have been developed for laboratory species and these have been successful in producing live young. IVG in association with IVM and cryopreservation have the potential to maximize the genetic potential of high genetic merit females and shorten generation intervals. This paper presents the current status of technology for the in vitro growth and development of immature oocytes, in vitro maturation and cryopreservation of germ cells in domestic ruminants.
Factors affecting folliculogenesis in ruminants
- R. Webb, R. G. Gosden, E. E. Telfer, R. M. Moor
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- Journal:
- Animal Science / Volume 68 / Issue 2 / March 1999
- Published online by Cambridge University Press:
- 18 August 2016, pp. 257-284
- Print publication:
- March 1999
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This review addresses the reasons for the lack of progress in the control of superovulation and highlights the importance of understanding the mechanisms underlying follicular development. The present inability to provide large numbers of viable embryos from selected females still restricts genetic improvement, whilst variability in ovarian response to hormones limit the present capacity for increasing reproductive efficiency.
Females are born with a large store of eggs which rapidly declines as puberty approaches. If these oocytes are normal then there is scope for increasing the reproductive potential of selected females. Oocytes must reach a certain size before they can complete all stages of development and the final changes that occur late in follicular development. It is likely that oocytes that do not produce specific factors at precise stages of development will not be viable. Hence, it is important to characterize oocyte secreted factors since there are potential indicators of oocyte quality.
The mechanisms that determine ovulation rate have still not been fully elucidated. Indeed follicular atresia, the process whereby follicles regress, is still not known. A better understanding of these processes should prove pivotal for the synchronization of follicular growth, for more precise oestrous synchronization and improved superovulatory response.
Nutrition can influence a whole range of reproductive parameters however, the pathways through which nutrition acts have not been fully elucidated. Metabolic hormones, particularly insulin and IGFs, appear to interact with gonadotrophins at the level of the gonads. Certainly gonadotropins provide the primary drive for the growth of follicles in the later stages of development and both insulin and IGF-1, possibly IGF-2, synergize with gonadotrophins to stimulate cell proliferation and hormone production. More research is required to determine the effects of other growth factors and their interaction with gonadotropins.
There is evidence, particularly from studies with rodents, that steroids can also modulate follicular growth and development, although information is very limited for ruminants. There may be a rôle for oestrogens in synchronizing follicular waves, to aid in oestrous synchronization regimes and for removing the dominant follicle to achieve improved superovulatory responses. However more information is required to determine whether these are feasible approaches.
Heritability for litter size is higher in sheep than in cattle. Exogenous gonadotropins are a commercially ineffective means of inducing twinning in sheep and cattle. Although there are differences in circulating gonadotropin concentrations, the mechanism(s) responsible for the high ovulation appear to reside essentially within the ovaries. The locus of the Booroola gene, a major gene for ovulation rate, has been established but not specifically identified. However sheep possessing major genes do provide extremely valuable models for investigating the mechanisms controlling ovulation rate, including a direct contrast to mono-ovulatory species such as cattle.
In conclusion, the relationship between oocyte quality, in both healthy follicles and those follicles destined for atresia, must be resolved before the future potential for increasing embryo yield can be predicted. In addition, a greater understanding of the factors affecting folliculogenesis in ruminants should ensure that the full benefits ensuing from the precise control of ovarian function are achieved. The improved use of artificial insemination and embryo transfer that would ensue from a greater understanding of the processes of folliculo genesis, coupled with the new technologies of genome and linkage mapping, should ensure a more rapid rate of genetic gain.
Investigating early agriculture in Central Asia: new research at Jeitun, Turkmenistan
- D. R. Harris, V. M. Masson, Y. E. Berezkin, M. P. Charles, C. Gosden, G. C. Hillman, A. K. Kasparov, G. F. Korobkova, K. Kurbansakhatov, A. J. Legge, S. Limbrey
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In 1989 ANTIQUITY published a special section of papers on the archaeology of the steppe zone, to notice the special role of that great sweep of land that links the northern fringes of early prehistoric agriculture in Europe and Asia. A new international team has now returned to Jeitun, the key early agricultural site in Turkmenistan, on the edge of the Kara Kum desert.
10 - Transplantation of ovaries and testes
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- By R. G. Gosden, Department of Physiology, University Medical School, Teviot Place, Edinburgh EH8 9AG, UK.
- Edited by Robert G. Edwards
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- Book:
- Fetal Tissue Transplants in Medicine
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- 05 November 1992, pp 253-280
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Summary
FEW SUBJECTS IN EXPERIMENTAL SURGERY have attracted as much public interest or professional controversy as the transplantation of testes and ovaries. At one time hailed as a cure-all for old age, clinical transplantation of gonads was eventually overtaken by advances in chemical endocrinology and transplantation biology and is now regarded mainly as one of the blind alleys of science. The legacies of the so-called rejuvenators have effectively smothered further consideration of transplantation as a potential treatment for hypogonadism.
The first authenticated record of gonadal transplantation is attributed to an eighteenth century Scottish anatomist and surgeon, John Hunter, who grafted chicken testes and ovaries to the body cavity of hosts of either the same or opposite sex. Full details of this work have not survived and it is difficult to evaluate his claims but, since he used allografts, it seems doubtful that he could have been successful. Persistent scar tissue or hypertrophy of host gonads that were incompletely extirpated may explain his claims to success. Such dangers of misinterpretation can account for many false positive findings in a later era and for much of the confusion that followed.
It is the Gottingen biologist, Berthold (1849), who should be credited with the first successful testicular transplants, since, by using autografts, he luckily avoided the risk of rejection. When he replaced the testes of capons in their own body cavity he found that the growth of comb, plumage and courting behaviour, all of which are androgen dependent, were maintained. The transplantation of ovaries was pioneered in France by Bert (1865), but several decades passed until interest in either technique became widespread.
The turn of the century signalled an explosion of interest in gonadal transplantation. One causal factor was the dawning of the new science of endocrinology and the opportunities that transplantation offered for experimentally testing hormone secretion and action. Knauer (1896) autotransplanted rabbit ovaries to the broad ligament and peritoneal cavity and obtained evidence of normal function, including ovulation and prevention of uterine atrophy. Like most of his contemporaries, he regarded allografting as potentially successful, but failed to provide any convincing evidence to support this assumption. The first investigator to transplant fetal ovarian tissue was Foa in 1900. He made the important discovery that immature organs undergo accelerated maturation in an adult environment.