Bioscientifica Proceedings

Abstract unavailable© 1987 Journals of Reproduction & Fertility Ltd...

Summary. Several manipulation techniques including nuclear injections, nuclear transplantation, embryo splitting, chimaera production and sperm injection are discussed with special reference to their application in the pig. The nuclear injection technique is likely to be of greatest use for gene transfer. Gene transfer is feasible for pig embryos. but it is very inefficient. Efficiencies of various steps in the successful production of transgenic offsprin...

Summary. Nuclear transfer for the study of differentiation in amphibians has been used since the 1950s, but not until recently have the same procedures been applied successfully to some mammals. Nuclear transfer, as developed for the amphibian, is successful in sheep, cattle, rabbit, and pig, but not mouse embryos. This fact is discussed in relation to the species-specific timing of the activation of the zygotic genome. Nuclear transfer to an oocyte presu...

Summary. Embryos of amphibians, sheep, cattle, pigs and rabbits have been multiplied by nuclear transfer. Successful nuclear transfer in these species has been accomplished by transfer of a blastomere from a late-stage embryo into an enucleated oocyte with large scale multiplication by repeating the procedure using blastomeres from the embryos produced from nuclear transfer. This allows the production of clonal lines which, when appropriately selected for perf...

Abstract unavailable© 1982 The authors...

Early follicular growth refers to the development of an ovarian follicle from the primordial to early antral phase. In sheep and cows these phases of growth can be classified by the configuration of granulosal cells in the largest cross–section of the follicle as types 1 (primordial), la (transitory) 2 (primary), 3 and 4 (preantral) and 5 (early antral). Follicles classified as type 1 may be highly variable within each species with respect to number of granulosal cells an...

Determining the stage- and tissue-specific patterns of gene expression shown by the embryo and fetus will provide information about the control of normal development. Identification of alterations in these patterns associated with specific abnormal phenotypes will also be informative regarding the underlying molecular mechanisms. In addition, qualitative and quantitative changes in gene expression that deviate from the norm may provide a potential marker system for predicting ...

Gender preselection using isolated populations of X- and Y-chromosome bearing spermatozoa that have been separated on the basis of DNA content is currently possible in swine and other farm animals, as well as in humans. Semen from most livestock species can now be successfully separated into predominantly X or Y sperm populations before their use for intra-tubal insemination, deep-uterine insemination or for in vitro fertilization (IVF) to produce sexed offspring. Birth o...

Summary. Early embryo mortality during the first two weeks of development is an important factor in the decreasing fertility of dairy cattle. During this period the embryo needs to correctly establish the first three lineages, namely epiblast, hypoblast and trophoblast so as to survive. The morphological and molecular events underlying these lineage decisions are discussed, drawing on information derived predominantly from mice and cattle.<p class="abstext...

As milk production has increased during the past four decades, conception rates in lactating cows have declined. Although reduced reproductive performance has been associated with high milk yields, measures of postpartum ovarian activity have been more closely related to energy balance. The relationship between daily energy balance and postpartum reproductive activity is confirmed by longer intervals to first ovulation in cows with greater body condition loss. Patterns in dail...