Developmental potential of oocytes collected from 8–15 day old unstmulated or FSH treated calves

Enhanced efficiency in the production of offspring from 4- to 8-week-old lambs

The rate of production of offspring from lambs following the transfer of embryos produced by in vitro maturation and fertilisation has been disappointing. This study was conducted on the rationale that gonadotropin treatment protocols used in the past failed to maximise oocyte quality. Consequently, three experiments were conducted in Merino lambs to examine: (1) the method of FSH administration (single versus multiple treatments), (2) the time of oocyte collection (48, 60 or 72 h after the first FSH treatment), (3) progesterone treatment and (4) eCG treatment and its timing on oocyte yield, cleavage rate and blastocyst formation rate. No factor significantly influenced oocyte yield, but all significantly influenced the rates of cleavage and/or blastocyst formation in one or more experiments. The preferred protocol consisted of the administration of 4x40 mg of FSH, no progesterone treatment and with 500 IU of eCG given at the time of the last FSH treatment. The optimal time of oocyte collection was 48 h after the first FSH treatment. A field evaluation, involving lambs from five generations, resulted in the production of 9.0-13.9 lambs per donor lamb; this protocol generated more lambs per donor lamb than protocols previously reported.

Effect of in vitro and in vivo culture on embryo development from prepubertal goat IVM-IVF oocytes

The aim of this study was to analyze different culture systems on embryo development of prepubertal goat oocytes. We compare (i) the effect of the age of donor (goat) of oocytes on in vitro maturation, fertilization and subsequent embryo development, (ii) the effect of the origin of oviduct cells from coculture of prepubertal goat embryo development, and (iii) the effect of in vivo culture in rabbit oviducts for 1, 2 and 3 days on the development of prepubertal goat embryos produced in vitro. In Experiment 1, at 24 h post-insemination (hpi), oocytes from adult goats were allocated in TCM199 with oviduct cells from adult goats, and oocytes from prepubertal goats were randomly placed in drops with oviduct epithelial cells from adult (aOEC) or prepubertal (pOEC) goats. Cleavage rate and embryo development were evaluated at 48 hpi and after 7 days coculture, respectively. In Experiment 2, at 24 hpi, prepubertal oocytes were allocated in TCM 199 with pOEC. At 40-42 hpi, a group of embryos remained in the coculture (control group), and the rest were transferred to rabbit oviducts (three rabbits for replicate) for culturing in vivo for 24, 48 and 72 h. After these in vivo cultures, embryos were recovered, evaluated and placed in TCM199 with pOEC until Day 8 post-insemination. The maturation, fertilization and blastocyst rates did not differ significantly between oocytes obtained from adult and prepubertal goats. The percentage of blastocysts obtained from prepubertal goat embryos cocultured with aOEC or pOEC was also similar (12.1% versus 12.2%). The transfer of prepubertal goat embryos to rabbit oviducts for 1, 2 and 3 days did not improve the blastocyst rate compared to the control group (9.7, 10.9, 4.1 and 11.5%, respectively). In conclusion, in our conditions, there were no significant differences in embryo development between oocytes obtained from prepubertal and adult goats, and the embryo development from prepubertal goat oocytes were similar in the different culture systems compared.

Effects of maternal age on oocyte developmental competence

The widespread use of a variety of assisted reproductive technologies has removed many of the constraints that previously restricted mammalian reproduction to the period between onset of puberty and reproductive senescence. In vitro embryo production systems now allow oocytes from very young animals to undergo fertilization and form embryos capable of development to normal offspring, albeit at somewhat reduced efficiencies compared to oocytes from adult females. They also can overcome infertility associated with advanced age of animals and women. This review examines oocyte developmental competence as the limiting factor in applications of assisted reproductive technologies for both juvenile and aged females. Age of oocyte donor is a significant factor influencing developmental competence of the oocyte. Age-related abnormalities of oocytes include a) meiotic incompetence or inability to complete meiotic maturation resulting in oocytes incapable of fertilization; b) errors in meiosis that can be compatible with fertilization but lead to genetic abnormalities that compromise embryo viability; and c) cytoplasmic deficiencies that are expressed at several stages of development before or after fertilization. In general, oocytes from juvenile donors and the embryos derived therefrom appear less robust and may be less tolerant to suboptimal handling and in vitro culture conditions than are adult oocytes. Research to identify specific cytoplasmic deficiencies of juvenile oocytes may enable modifications of culture conditions to correct such deficiencies and thus enhance developmental competence. Use of oocytes from aged donors for assisted reproduction can have a variety of applications such as extending the reproductive life of individual old females whose offspring still have high commercial value, and conservation of genetic resources such as rare breeds of livestock and endangered species. In general, female fertility decreases with advancing age. Studies of women in oocyte donation programs have established reduced oocyte competence as the major cause of declining fertility with age, although inadequate endometrial function can also be a contributing factor. Most research has emphasized the importance of chromosomal abnormalities because of the well established increase in aneuploidy with increasing maternal age but little is known about the underlying cellular and molecular mechanisms. Research aimed at identifying the specific developmental deficiencies of oocytes from juvenile donors and abnormalities of oocytes from aged females will assist in overcoming present bottlenecks that limit the efficiency of assisted reproduction technologies. Such research will also be crucial to the development of new oocyte-based technologies for overcoming infertility and possibly subverting chromosomal abnormalities in women approaching menopause.

In vivo oocyte recovery and in vitro embryo production from bovine donors aspirated at different frequencies or following FSH treatment

The effects of frequency of follicular aspiration and treatment of donor cattle with FSH on in vivo oocyte recovery and in vitro embryo production were studied. Simmental heifers (n = 24) formed 8 replicates of 3 treatments in which oocyte donors were aspirated 1) once a week, 2) twice a week, or 3) once a week following treatment with FSH for 3 d prior to aspiration. Oocytes were graded, washed, matured for 20 to 24 h and then inseminated with frozen/thawed semen from a single sire, followed by co-culture on granulosa cell layers. Embryo development was observed until Day 7 after insemination. Significantly fewer follicles per heifer per week were counted (14.7+/-2.3 vs. 27.4+/-3.1 vs. 23.1+/-2.8) and aspirated (12.0+/-2.0 vs. 21.8+/-2.7 vs. 20.1+/-2.6) in heifers on the once-weekly than twice-weekly aspiration treatment (P<0.01) or on the once-weekly aspiration after FSH treatment (P<0.05). There were no significant differences between treatments in the total number of oocytes recovered per week (5.6+/-1.2 vs. 8.9+/-1.5 vs. 6.1+/-1.2), but significantly more oocytes per heifer per week recovered from animals treated with FSH were graded Category 1 (2.8+/-0.4), i.e., >4 layers good cumulus with a clear, even cytoplasm, than from animals aspirated once (0.9+/-0.2; P<0.01) or twice a week (1.5+/-0.3; P<0.05). The number of transferable morulae plus blastocysts produced per heifer per week was higher from animals aspirated twice a week (2.4+/-0.4; P<0.05) or once a week following FSH treatment (2.1+/-0.4; P<0.05) than from animals aspirated once a week without FSH treatment (1.0+/-0.3). In conclusion, FSH treatment of bovine oocyte donors aspirated once a week enabled a similar number of transferable embryos to be produced per donor week as aspiration twice a week without FSH treatment. These 2 treatments produced twice as many transferable embryos per donor week as aspiration once a week without FSH treatment.