Embryo transfer and related technologies in sheep reproduction

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Recently developed, assisted reproductive technologies (e.g., in vitro embryo production and nuclear transfer) have encountered perinatal morbidity/mortality of the offspring produced, which are likely to hinder the application of these techniques. Consequently we have sought to develop a system of hormonal stimulation that will ensure the delivery of offspring more prepared for extrauterine life. Here we examine deliveries outcome in sheep carrying in vitro-produced and nuclear transfer (NT) embryos in comparison to artificially inseminated and naturally mated control ewes. All groups (excluding NT, which received one treatment) were subjected to one of two hormonal treatments for induction of delivery, whereas the third part of each group was left without any treatment. The first (commonly used for naturally mated ewes) dexamethasone treatment did not solve a majority of parturition disturbances, and actually the number of deliveries necessitating assistance was reduced (P < 0.05) by this treatment in the control group. On the other hand, combined estradiol plus betamethasone stimulation (E + B) solved a majority of complications regarding delivery performance such as lack of the preparation of the mammary gland, low myometrial contractility, insufficient cervical ripening, and impaired maternal behavior. Moreover, substantial reduction of neonatal mortality was observed following the combined treatment. In conclusion, the E + B induction of delivery overcame the majority of physiological and behavioral intrapartum failures of sheep foster mothers and increased the survival of offspring, and thus can be recommended as a safe method for inducing delivery in foster mothers carrying in vitro-generated embryos.

Section: Discussionsupporting

confidence: 67%

Improving Delivery and Offspring Viability of In Vitro-Produced and Cloned Sheep Embryos1

Ptak

Clinton

Tischner

et al. 2002

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“…Wells et al [12] achieved a rate of 27.5% blastocysts when cultured adult mural granulosa cells were exposed to a cytoplast for a prolonged period of 4-6 h prior to activation; however, a direct comparison between IA and a 4-to 6-h incubation prior to activation (DA) was not performed in their study. The discrepancies in the results from various studies might also be explained by differences in selecting somatic donor cells (bovine embryonic stem-like cells vs. somatic cumulus cells) [31], age of oocyte recipients [32], experimental conditions [23], and protocols used [32][33][34]. Akagi et al [32] found that the DA method improved the in vitro development potential of NT embryos.…”

Section: Discussionmentioning

confidence: 99%

Premature Chromosome Condensation Is Not Essential for Nuclear Reprogramming in Bovine Somatic Cell Nuclear Transfer1

Sung

Shen

Jeong

et al. 2007

Premature chromosome condensation (PCC) was believed to promote nuclear reprogramming and to facilitate cloning by somatic cell nuclear transfer (NT) in mammalian species. However, it is still uncertain whether PCC is necessary for the successful reprogramming of an introduced donor nucleus in cattle. In the present study, fused NT embryos were subjected to immediate activation (IA, simultaneous fusion and activation), delayed activation (DA, activation applied 4 h postfusion), and IA with aged oocytes (IAA, activation at the same oocyte age as group DA). The morphologic changes, such as nuclear swelling, the occurrence of PCC, and microtubule/aster formation, were analyzed in detail by laser-scanning confocal microscopy. When embryos were subjected to IA in both IA and IAA groups, the introduced nucleus gradually became swollen, and a pronuclear-like structure formed within the oocyte, but PCC was not observed. In contrast, delaying embryo activation resulted in 46.5%-91.2% of NT embryos exhibiting PCC. This PCC was observed beginning at 4 h postcell fusion and was shown as one, two, or multiple chromosomal complexes. Subsequently, a diversity of pronuclear-like structures existed in NT embryos, characterized as single, double, and multiple nuclei. In the oocytes exhibiting PCC, the assembled spindle structure was observed to be an interactive mass, closely associated with condensed chromosomes, but no aster had formed. Regardless of whether they were subjected to IA, IAA, or DA treatments, if the oocytes contained pronuclear-like structures, either one or two asters were observed in proximity to the nuclei. A significantly higher rate of development to blastocysts was achieved in embryos that were immediately activated (IA, 59.1%; IAA, 40.7%) than in those for which activation was delayed (14.2%). The development rate was higher in group IA than in group IAA, but it was not significant (P = 0.089). Following embryo transfer, there was no statistically significant difference in the pregnancy rates (Day 70) between two of the groups (group IA, 11.7%, n = 94 vs. group DA, 12.3%, n = 130; P > 0.05) or live term development (group IA, 4.3% vs. group DA, 4.6%; P > 0.05). Our study has demonstrated that the IA of bovine NT embryos results in embryos with increased competence for preimplantational development. Moreover, PCC was shown to be unnecessary for the reprogramming of a transplanted somatic genome in a cattle oocyte.

“…Embryo production from hormonally stimulated ewes (multiple ovulation and embryo transfer, MOET; ovum pick-up, OPU) is hindered by an unpredictable ovarian response [1]. A recent survey reveals that about 20% of sexually mature ewes do not respond to superovulatory treatments [2].…”

Section: Introductionmentioning

confidence: 99%

“…Even higher proportions of poor-or nonresponding donors were confirmed in prepubertal lambs [3][4][5] and calves [6]. 1 In ruminants, the variability in follicular response and capacity for embryos can be caused by several environmental factors like nutrition [7][8][9][10], management of animals [1,11], and season or photoperiod [2]. Another factor influencing developmental competence of oocytes is the timing of hormonal stimulation relative to the stage of estrus cycle [12].…”

Section: Introductionmentioning

confidence: 99%

Donor-Dependent Developmental Competence of Oocytes from Lambs Subjected to Repeated Hormonal Stimulation1

Ptak

Tischner

Bernabò

et al. 2003

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An unpredictability of ovarian response still remains the major problem concerning ovine reproductive programs. The influence of several environmental, genetic, and ovarian cycle effects on oocyte/embryo yield from donor females has been previously reported. The present research has been designed to exclude aforementioned causes of variability, thus to verify embryogenic competence in homogenous groups of animals. For this purpose we used prepubertal ewes kept under identical conditions. Initially, we stimulated three groups of prepubertal ewes at various ages and used a number of gonadotropin treatments to assess differences in oocyte competence between individuals. The results revealed the repeatability of response within individual donor lambs throughout the study. Moreover, once the variability in both oocyte and embryo yield between homogenous groups of donors was revealed alongside the influence of age and type of gonadotropin treatment (P < 0.001), we investigated whether the individual donor effect persisted among genetically similar animals. Therefore, we compared oocyte and subsequent embryo output of sibling lambs derived from the most efficient donor. Here the genetic homogeneity of sisters kept under identical conditions substantially improved the uniformity of either follicular response or embryo production, suggesting that the genotype plays a primary role in establishing follicular recruitment and developmental capability of oocytes. This observation consents to predict the ovarian performance from a single ewe already in early prepuberty (i.e., to qualify the female to breeding programs).