1,721,183 research outputs found
Recent advances in fertility preservation of dogs and cats
No full textStrategies to preserve fertility in dogs and cats as cryopreservation of epididymal spermatozoa, oocytes
and ovarian tissue will be discussed in this review . Recent results indicate that significant progress have been achieved, but optimal freezing protocols have not been defined yet. The extreme sensitivity of sperm membranes and of oocyte and ovarian tissue structur e deserves further investigations aimed at protecting male and female gametes from freezing injuries
Slow freezing vs vitrification for oocyte and embryo cryopreservation in the cat
No full textStudies were conducted to examine the effects of the cyclicity and the presence of a dominant follicle (DF) in ovary on the recovery and in vitro growth of pre-antral follicles (PFs) in sheep and buffalo. Small pre-antral follicles (SPFs, 100-250 μm) and large pre-antral follicles (LPFs, 250-450 μm) were isolated from slaughterhouse ovaries in the breeding seasons by a mechanical and enzymatic method. The sheep and buffalo PFs were cultured in vitro for 6 and 15 days, respectively, and examined for their growth, survival and antrum formation rates and growth rates of oocytes in cultured pre-antral follicles. The follicles of the sheep and buffalo were recovered and cultured simultaneously within replicates. The recovery rates (number per ovary) of both SPFs and LPFs were significantly (p < 0.05) higher in cyclic ewes (SPFs: 22.0 ± 3.3 vs 12.1 ± 2.6 and LPFs: 16.0 ± 3.6 vs 9.2 ± 1.8) and buffaloes (SPFs: 9.2 ± 1.3 vs 4.1 ± 1.0 and LPFs: 10.3 ± 2.7 vs 5.4 ± 0.7) compared with those recovered from acyclic ones. Presence of a DF in ovary significantly (p < 0.05) reduced the recovery rates of LPFs in ewes (9.06 ± 2.7 vs 16.4 ± 3.8) but had no effect in buffalo. Cyclicity of animals or follicular dominance had no effects on in vitro growth, survival and antrum formation rates and growth rates of oocytes in cultured PFs of SPFs and LPFs in both sheep and buffalo. The in vitro growth, survival and antrum formation rates of LPFs and growth rates of oocytes in cultured LPFs were significantly (p < 0.05) higher than those observed in SPFs in both sheep and buffalo. The overall recovery and growth rates of the PFs were lower in buffaloes compared with ewes
Clinical application of reproductive biotechnologies in dogs and cats
No full textAssisted reproductive techniques (ART) are aimed to the improvement of reproductive performances. Manipulation of the gametes outside the bodies of the originating organisms is the core of reproductive biotechnologies. Besides Artificial Insemination (IA) widely applied particularly in dogs, other techniques that imply both sperm and oocyte manipulation in vitro have been developed in several mammalian species including dogs and cats. In vitro embryo production, achieved significant advances particularly in cats, and sperm-oocyte interaction in vitro represents a powerful tool for testing male gametes
In vitro oocyte maturation in Canids: biological and technical pitfalls
No full textThe efficiency of oocyte in vitro maturation in Canids is characterized by a low and greatly variable success. The reason may lie in a very peculiar morphological and functional characteristic of Canid oocyte folliculogenesis and maturation. The selection of oocytes which had acquired the ability to undergo meiotic maturation, through adequate intrafollicular growth, is important for in vitro maturation. Moreover, the identification of parameters indicative of meiotic competence could help in the understanding of the mechanisms which limit the maturation rates in these species.
In dogs some of these parameters have already been identified. It has been shown that the size of oocytes is important for their ability to mature in vitro and oocytes with a diameter >100 m have a better chance to reach the metaphase II (Hewitt and England, Theriogenology 1998, 49:957-966). In addition, it has been reported in the fox that oocytes with diameters up to 100 m are meiotically incompetent (Srsen et al., Zygote 1998, 6:299-309). Moreover, advanced preantral and early antral follicles dissected from canine ovaries and cultured in vitro show that their oocytes are competent to resume meiosis to the metaphase II stage (Bolamba et al., Theriogenology 1998, 49: 933-942). Preovulatory maturation is required for the normal development of canine oocytes, although they are ovulated at the germinal vesicle stage. In fact, canine oocytes collected from ovaries before the preovulatory intrafollicular maturation (anoestrous) have lower rates of maturation than oocytes collected from preovulatrory follicles of superovulated bitches (Yamada et al., J. Reprod. Fertil. 1993 Suppl. 47: 227-229).
Oocyte and cumulus cell morphology is also important for selecting oocytes. Nickson et al. (J. Reprod. Fertil. 1993 Suppl. 47: 231-240) reported that only oocytes with at least two layers of closely applied cumulus cells are committed to develop in culture.
The immature stage of oocytes at ovulation and the persistence of cumulus cells that remain attached in a tight and multilayered mass during the transport and maturation period within the oviduct suggested that the investigation of the communications through gap junctions between the somatic compartment of the follicle and the oocyte, could help to identify competent oocytes. It is well known that such communications are involved in the acquisition of meiotic and developmental competence, and it has been reported in the fox that all junctional contacts between cumulus cells and oocyte are disrupted when metaphase I is reached in vivo (Hyttel et al., Anat Embryol. 1990, 181: 325-331). Moreover, the cumulus, mainly corona radiata cells, controls resumption of meiosis of fox oocytes either in vivo or in vitro conditions (Srsen et al., Zygote 1998, 6:299-309).
Recent results (Luvoni et al., J. Reprod. Fertil Suppl., in press) have demonstrated that the functional status of cumulus cells-oocyte communications, through gap junctions, is influenced by the stage of the cycle, and that oocytes collected during late proestrous are capable of completing meiosis at a higher rate than oocytes collected during anoestrous. This suggests that the stage of the cycle at the time of collection influences oocyte meiotic competence.
Thus, oocyte diameter, cumulus conformation as well as follicular developmental stage and stage of the cycle are important selection parameters for successful oocyte in vitro maturation in Canids
Cryosurvival of ex situ and in situ feline oocytes
Full text linkSignificant advances in feline oocytes cryopreservation have recently been achieved. The oocyte is considered more susceptible to cooling damage than embryos and spermatozoa, however recent results demonstrate that banking of cryopreserved female gametes is an attainable goal. In Felids, as well as in other mammals, oocyte cryopreservation would significantly contribute to the improvement of assisted reproductive technologies aimed to the preservation of biodiversity. Besides the advantages in animal conservation, the use of animal models, as domestic cat, provides the opportunity for further investigations of the principles of oocyte cryobiology which can help to improve current technologies applied to both humans and animals. A review of the literature regarding survival of feline oocytes cryopreserved as isolated cells (ex situ) or enclosed in ovarian follicles (in situ) is provide
Current progress on assisted reproduction in dogs and cats
No full textThe objective of the development of assisted reproduction techniques in dogs and cats is their application to non-domestic canine and feline species, most of which are considered threatened or endangered.
In the last decade, progress has been made in assisted reproduction techniques in carnivores and a entirely in vitro system for embryo production is an important tool for conservation of wildlife.
It has been shown that canine oocytes can resume meiosis in vitro and that oocytes can be fertilized and developed in vitro, although at a much lower rate than most other domestic animal oocytes. The reason lies in the dissimilarities of reproductive physiology of the dog compared to other species and the lack of precise information concerning the oviductal environment, in which oocyte maturation, fertilization and early embryonic development take place.
Successful in vitro embryo production in the domestic cat has been attained with oocytes matured in vitro and kittens were born after transfer of IVM/IVF derived embryos. On the basis of these results the in vitro fertilization of oocytes has also been applied in several non-domestic feline species.
The effectiveness of such protocols in the preservation of genetic material of rare species can be improved by developing better techniques for long-term storage of gametes. In dogs and cats sperm cells have been successfully frozen and the cryopreservation of oocytes would greatly increase their availability for a range of reproductive technologies.
It has been demonstrated that cryopreserved cat oocytes can be fertilized successfully and that their development in vitro after fertilization is enhanced when mature oocytes are frozen.
Thus refined techniques of oocyte maturation and fertilization in vitro coupled with oocyte cryopreservation could allow for an easy establishment of genetic combinations when male and female gametes in the desired combination are not simultaneously available, and the propagation of endangered carnivores would be facilitated
Cryobanking of oocytes and ovarian tissue in cats and dogs
No full textCryobanking of female gametes has important potential applications in carnivores. The availability of cryostored oocytes or gonadal tissue, as reservoir of a large number of oocytes, would greatly improve assisted reproductive techniques aimed at ensuring the future survival of high genetic value individuals.
Long-term storage of gametes would allow the planning of in vitro embryo production and transfer at proper time, that is, whenever male gametes and embryo recipients are available. It would also maintain genetic diversity that would otherwise be lost when an animal dies or is gonadectomized.
This is particularly crucial in wild and rare species threatened by extinction or in domestic valuable breeds
Ultrasonographic study of gestation in dogs and cats
No full textUltrasonographic examination provides useful information for monitoring fetal growth and for assessing
gestational age. Among a wide variety of ultrasonographic fetal measurements, the diameter of the inner chorionic cavity (ICC) during early pregnancy and the biparietal (BP) diameter during late pregnancy are highly correlated with the gestational age and both highly reliable for the prediction of parturition term when specific formulae for different size bitches and for queens are applied. In clinical practice the prediction of parturition term is particularly valuable for planning clinical assistance of whelping or elective caesarean sections
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