Particularity of reproductive cycles of
Abstract
The growth of the human population and the escalating consumption of natural resources have reduced wild habitats, modifying the existing balance of biological cycles. Therefore, ex situ conservation efforts have received renewed attention as a potential safeguard for species with an uncertain future in the wild. Most wild felid species are classified as rare, vulnerable, or endangered due to poaching and habitat loss. Any directed action taken by humans to enhance animal reproduction results in assisted reproductive technologies (ART) development. These technologies have been included in programs for the conservation of endangered species. Therefore, ART provide a new approach in the safeguard programs of felid biodiversity. Currently, ART mainly include Artificial Insemination (AI); In Vitro Embryo Production (IVEP) consisting of In Vitro Maturation (IVM), In Vitro Fertilization (IVF), In Vitro Culture (IVC), Embryo Transfer (ET), and Intra Cytoplasmic Sperm Injection (ICSI); gamete/embryo cryopreservation; gamete/embryo sexing; gamete/embryo micromanipulation; Somatic Cell Nuclear Transfer (SCNT); and genome resource banking.
Keywords
- Assisted Reproductive Technologies (ART)
- In Vitro Embryo Production (IVEP)
- endangered feline species
1. Introduction
The growth of the human population and the escalating consumption of natural resources have reduced wild spaces, modifying the existing balance of the biological cycles. Therefore,
2. Reproductive cycles of wild felids
Knowledge of anatomical features and hormones and the cycles of wild reproductive feline is the ability to track feline reproductive activity. The hormone measure is a key technique to develop successful ex situ breeding programs to determine the reproductive activity of domestic feline. The ovaries in the wild felid and the domestic cat are caudal to the respective kidneys and connected proximally by the suspensor ligament and dorsally by the mesovaria. The oviducts are covered by the mesosalphinx that forms, laterally to the ovaries – an ovarian bursa. Each oviduct cranially is localized in the medial aspect of the ovarian bursa; caudally it is located in the lateral aspect before terminating at the uterotubal junction. The mesometrium suspends dorsally the horns of the uterus bicornuate. The uterine body is divided internally by an incomplete septum. The cervix is short, but it opens at an angle close to the vaginal orifice. The lips of the vulva are located just below the anus. After fertilization, the blastocysts are distributed evenly along the uterine horns, with an efficient result of transuterine migration. Cats have a zonary endotheliochorial type placenta. Regarding the hormone profile of wild felines, reasonable results were obtained by noninvasive monitoring of steroid [14]. Reproductive cycle models of ovarian steroids have now been published about half of nondomestic felid species, by analysis of fecal steroid metabolites. There are four phases of the oestrous cycle in the cat: proestrus, oestrus, diestrus, and anestrus (or interestrus) [15]. Proestrus usually lasts less than a day, and is associated with the presence of ovarian follicles, increased circulating estrogens, no sexual interest but occasionally there could be copulation with the male. Oestrous has maximum concentrations of follicular estradiol. It is characterized by coitus and, depending on the species, by special and typical behaviors such as vocalization, rubbing, rolling, lordosis, and foot stamping. The release of gonadotrophins-releasing hormone (GnRH) from the basal medial hypothalamus and successive waves of luteinizing hormone (LH) from the anterior pituitary gland, are considered necessary in most felines [16, 17]. This cascade of events will result in ovulation after mating. Surges of estrogens distinguish oestrous from interestrus periods, with cycles ranging from 2 to 4 weeks and oestrus lasting 3–10 days. Cats have historically been categorized as having “induced ovulation,” that is, requiring mating to stimulate ovulation. Nevertheless, we now know that felids exhibit a range of ovulatory patterns, from almost exclusively induced to manifold combinations of induced and spontaneous ovulation. There are differences not only across species, but also between individuals within a species [14]. In fact, spontaneous increase in progestogens after oestrogen surges is rare or inexistent in the tiger (
Several studies report the domestic cat be seasonally poly oestrous animal with positive photoperiod under natural [16]. In general, ovarian cyclic activity and reproductive functions are reduced under decreasing photoperiod and starts again after exposure to increasing light. In the cat, melatonin seems to regulate photoperiod-induced seasonality. The highest concentrations happen during the dark phase [17]. Reproduction is in someway seasonal in many nondomestic felids like the tiger, pallas’cat, clouded leopard, snow leopard, and lynx (Table 1). The follicular activity, conversely, is not influenced by season in lions, bobcats, pumas, leopards, margays, tigrinas, ocelots, jaguars, and fishing cats [14]. Progestogen concentrations during pregnant and nonpregnant luteal phases are quantitatively similar in nondomestic felids and domestic cats [15].
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Domestic cat | 6–9 months | YES | YES | 3-16 days | 58–65 days |
Cheetah | 2–3 years | NOT | YES | 2–6 days | 94 days |
Pallas cat | 1 year | YES | OCCASIONALLY NOT | 3–14 days | 66–77 days |
Clouded leopard | 2 years | YES | NOT (40%) | 3–6 days | 90 days |
Tiger | 3–4 years | YES | YES | 7 days | 108 days |
Leopardis species | 1–2 years | YES /NOT | NOT | 2–7 days | 75–85 days |
Linx | 1–2 years | YES | YES | 7 days | 60–70 days |
Lion | 3 years | NOT | NOT | 5–6 days | 108 days |
Felids express marked variations in reproductive mechanisms among species. Two characteristics impact both natural and assisted breeding efforts: effect of seasonality on reproduction and identifying the type of ovulation (induced
3. Oestrus induction in felids
In the late of 1970s, various doses and single versus multiple treatments with either a pituitary extract of porcine FSH (approximately 10–20 mg) or eCG for stimulation of follicular development and induction of oestrus was evaluated [15]; 2.0 mg FSH per day until oestrus was observed to be the optimal dose of FSH despite the elevated average ovulation rate and the presence of residual follicles observed after treatment. Cats in the latter group were given the optimal dose of FSH as determined previously [15]: 2.0 mg/ day for 5 days ¼ 10 mg FSH. In the mid-1980s, the Center for Reproduction of Endangered Wildlife of the Cincinnati Zoo established a domestic cat colony model for developing assisted reproductive technologies to apply in conservation efforts for endangered species. The domestic cat, in addition to its prototypical role, was envisioned as a potential recipient of embryos from other species of similarly sized nondomestic cats, of which most are classified as threatened or vulnerable to extinction. In view of previous results in exogenous gonadotropins for oestrous induction, initial emphasis was directed at determining optimal FSH treatment regimes for ovarian follicular stimulation. In a 1987 published article [19] on ovarian response and embryo recovery after treatment with various doses of FSH (2.75–8.0 mg total) and hCG (0–1500 IU) and natural mating, the greatest average number of viable embryos (15.8 morulae and blastocysts) was recovered from the group receiving 4.0 mg FSH/750 IU hCG. Unexpectedly, there was no difference in the average number of viable embryos recovered from donors given the least amount of FSH (2.75 mg total) versus the greatest amount (8.0 mg total): 6.9 versus 7.9. Also, in 1988, we made our one and only attempt to apply the same methods to a species of nondomestic cat, the serval (
4. Gamete recovery from nondomestic felids
The first step for ART development is the gamete recovery. Several methods have been reported for semen collection in animals, such as the use of an artificial vagina [21], digital masturbation of the penile bulb and electroejaculation [22], but only electroejaculation method may be used for gamete recovery from wild felids. In any case, the application on nondomestic cats is based on learning how to use these methods in the domestic cats. Electroejaculation is to obtain both epidydimal spermatozoon and spermatogonial germ cells. In female, oocytes are retrieved and recovered from both antral and preantral follicles in ovarian tissue transplantation [23].
5. Male gamete recovery in felids
With wild carnivores, electroejaculation is the method of choice due to the difficulty and risks involved in handling these animals. Electroejaculation occurs after introducing of a transrectal probe with three electrodes, connected to an electric stimulator that provokes a controlled electric stimulation to allow the ejaculatory reflex to work. The nerves that supply the reproductive organs are stimulated by a weak electric current. The probe is inserted 7–9 cm into the rectum and the electrodes are directed ventrally. It is necessary to take care to evacuate any feces from the rectum for this kind of manipulation. [24]. Different protocols of electroejaculation have been used by many researchers [15]. The authors reported three series for a total of 80 electric stimulations. The three series were divided in: 30 stimuli (10 stimuli at 2–4 V series 01), 30 stimuli (10 stimuli at 3–5 V series 02), and 20 stimuli (10 stimuli at 5 and 6 V series 03) for the collection of semen from South African cheetahs (
Spermatogenesis is a complex and very efficient process with the mitosis and the differentiation of spermatogonial stem cells in the basal membrane of seminiferous tubules where they are supported by Sertoli cells [33]. The spermatogonial stem cells in mammals are unique, and thus they can maintain their proliferation in adults: the genetic material can be passed from a generation to the subsequent one. Therefore, these cells are a valuable source for medical research, biological experimentation, agricultural biotechnology, and genetic modification of the species [34]. Recent studies on their recovery and cryopreservation showed the perspective of application in the conservation of genetic material from endangered animal species. Present methods described for spermatogonial isolation from fragments of collected testis consists of elutriation or sedimentation rate in a gradient of bovine serum albumin under gravity force action [35]. Some other isolation techniques have been proposed as immunological markers for posterior magnetic cellular separation [36]. After collection, germ cells can remain for several months in tissue culture media, only resuming spermatogenesis afterward in an environment that provides favorable conditions for their expansion and differentiation [37]. The favorable conditions are generally provided by transplant to other organisms [34]. The first success in the spermatogonial transplant was described by [38]. They showed that the microinjection of a cell heterogeneous suspension of mouse testis into the seminiferous tubules of a recipient sterile mouse resulted in spermatogenesis in the injected animal. After this study, several other researchers showed real possibilities such as the spermatogonial culture among different species: the xenograft [39]. It seems that cryopreservation of testis cell suspensions could be the greatest promise for the storage of germ cells to be used later in transplants. Indeed, after cryopreservation, spermatogenesis can continue [39]. In spite of the progress in this field, some elements remain to be controlled, such as the quantity of germ cells to be transplanted, formation of antibodies against spermatogonial cells by the recipient [40], and poor quality of cells that have developed using these procedures [41]. There is also a problem concerning xenograft related to the different time of spermatogenesis in each species [26, 42]. However, the complete spermatogenesis was observed after transplantation of testicular tissue fragments from species that are phylogenetically more distant, such as pigs and goats, into castrated immunodeficient mice. The new reproductive technologies on stem cells offer several potential advantages for carnivorous species. For example, the development of lines of embryonic stem cells in cats and dogs would allow the creation of a generation of transgenic animal models, which could be used to improve the health of both animals and humans. Techniques such as testis xenografting spermatogonial and stem cell transplantation offer new approaches to diffuse genetically valuable individual males, even if they should die before producing sperm. Therefore, these techniques could be applied to biomedical research, as well as to the programs for the conservation of endangered carnivore species. Recently, spermatogonial stem cell transplantation has been performed in a recipient able to produce sperm of donor genetic origin [26]. Sperm production, from prepubertal testis tissue from both ferrets and cats, was obtained from testis xenografting. These first steps reinforce the need for research on stem cell technologies and for complementary technologies of carnivore assisted reproduction, so clinical benefits and the largest array of research can be achieved [26].
6. Female gamete collection in felids
The ovarian follicular population seems to be made up of thousands of follicles in different mammalian females. Therefore, oocyte retrieval represents a rich source of genetic material to be used for genetic bank and assisted reproductive techniques in endangered species preservation, mainly in relation to the possibility of collecting material originated from postmortem or convalescent animals. The development of efficient methods for in vitro maturation (IVM) or fertilization (IVF) of oocytes collected postmortem or through ovariectomy is an important tool to prevent the species extinction [43-45]. Thus, IVM and IVF techniques are adjusted for several nondomestic animals [5] based on systematic studies in domestic animals [46] including wild carnivores. Moreover, application of oocyte and ovary tissue cryopreservation will help in the conservation of several animal species, with the objective of maintaining biodiversity [47]. Further, ultrasonographic images of the reproductive tract offer new opportunities for induction of sexual cycles and ovulation, adoption of superovulating regimens, as well as the ovum pickup application. Ovarian follicles are then visualized on a monitor, allowing oocyte collection by puncturing the follicles with a fine needle connected to a tube collector. The collected oocytes could be used in IVM and IVF [48, 49]. This technique is extensively used for oocyte collection in cattle and the findings indicate the possibility of repeated collections in both pregnant and nonpregnant females [50]. Concerning carnivorous species, ovum pickup using ultrasonography has yet to be reported. This may be due to the difficulty of ovarian visualization, because in bitches the ovary is surrounded by a pouch rich in conjunctive tissue [23]. Furthermore, there are no commercial probes developed for intravaginal use in either canids or felids. However, in spite of this difficulty, the presence of antral ovarian follicles can be detected by the fluid accumulation in the antral cavity [51]. A success in the follicular and corpora luteal visualization in ovaries of female African wild dogs (
A further alternative is represented by the ovarian tissue transplantation. [71] was the first to report an ovarian transplantation. Only in the twentieth century was a significant improvement of the vascular anastomosis techniques of several transplanted organs including the ovary achieved [72]. According to [73], both whole ovary and ovarian fragment transplantations could be used for ovarian follicle cultures. Moreover, [74] was reported that a great advantage for the preservation and culture of ovarian tissue is due to the possibility of material collection not dependent upon the age or reproductive status of the donor. Moreover, [75] suggested that the term allotransplantation refers to the transplantation of an organ originating from one individual to another that is genetically different, but belonging to the same species. Ovarian cortex fragments transplantation was successfully performed from domestic cats to the renal capsules of severely immunedeficient infertile mice [76]. After 9 months, the necropsy of the recipient mice was accomplished, when the presence of follicles was verified in the grafts. These ovarian follicles reached a 3 mm diameter, had a normal antral cavity, and appeared to be cytologically normal as follicle in integer cat ovary (Fig. 5). However, ovulation was not observed in any of the grafts. Furthermore, [77] reported that xenotransplanting into the kidney capsule from severe combined immunedeficient mice freeze–thawed of cat ovarian cortex did not allow its surviving, but the follicles containing gonadotropin responsive granulosa cells were able to grow to antral stages. Conversely, [78] declared that oocyte and ovarian tissue cryopreservation is not yet fully established. There are still several obstacles to overcome for this technology to be routinely used. Even so, improvement in the cryopreservation techniques is seen as an important tool for the formation of ovarian tissue banks, with the purpose of conserving precious genetic material of endangered species [79].
7. Gamete cryopreservation in felids
Cryopreservation of gametes is an important tool in assisted reproduction programs. In fact, long-term storage of oocytes or spermatozoa is necessary for in vitro fertilization (IVF) or artificial insemination (AI) in the future. When geographical or temporal distance between donors and recipient results in nonsimultaneous availability of male and female gametes, cryopreservation is the only option. Maintenance of biodiversity has intrinsic value for the genetic preservation of valuable domestic cat breeds and an extrinsic value for conservation management of taxonomically related nondomestic feline species. New knowledge about felid reproductive physiology will enhance the development of techniques that are potentially applicable to nondomestic cats. Domestic cat spermatozoa and oocytes have peculiar physical characteristics that increase the difficulty of developing successful cryopreservation methods as compared to gametes of some other species. Therefore, even though a variety of procedures have been investigated, optimal cryopreservation techniques, either for spermatozoa or oocytes, are yet to be realized [80]. Cat semen was successfully cryopreserved, and kittens were born after AI with frozen–thawed semen [81]. Achievements in cryopreservation of felid semen and different protocols of freezing–thawing ejaculated and epididymal cat semen have been reviewed [80]. In our laboratory we cryopreserved epididymal sperm felines with the following protocol: epididymides were collected from 20 domestic cats during routine neutering procedure and from two wild felines at autopsy. The sperm samples, diluted with 4% glycerol/Tris/egg yolk, were loaded into 0.25 ml mini-straws, exposed to nitrogen vapor and stored in liquid nitrogen. After 4 weeks, samples were thawed and reevaluated. The quality of each fresh and frozen–thawed sperm sample was tested by determining the motility (54.7±11.3% and 32±13.1%, respectively, for cat spermatozoa; 38.3±18.7% and 21.5±16.8%, respectively, for tiger spermatozoa), viability (74.3±8.6% and 45.2±9.4%, respectively, for cat spermatozoa; 42.4±14.5% and 33.5±12.9%, respectively, for wild felid spermatozoa), morphology, and acrosomal status. The present study showed that feline epididymal spermatozoa can be frozen in egg-yolk extender with 4.0% glycerol in 0.25 ml straws. The procedure used in the present study for epididymal cat sperm cryopreservation may be applied to bank for genetic resources of wild felid species. [82] Protocols for freezing/cryopreservation of cat oocytes [80] are established; nevertheless, this technology is still considered “experimental” because the survival rates of cat oocytes after freezing procedures are still low, but to date, there is evidence that some preantral follicles extracted from cat ovaries remain structurally intact and physiologically active after freezing/cryopreservation and subsequent thawing [80]. However, there is evidence that some preantral follicles from cat ovaries remain structurally intact and physiologically active after freezing/cryopreservation and subsequent thawing [70]. Domestic cat oocytes have high lipid droplet content in the ooplasm [83]; thus, oocyte permeability to cryoprotectant solutions may be lower than in oocytes of other species [84-87]. Only a few studies have investigated cat oocyte cryopreservation, and the few successes were only obtained for mature oocyte cryopreservation [80]. In the first study [80], mature and immature oocytes were cryopreserved by slow cooling, but no blastocysts were obtained after in vitro fertilization (IVF). In the second study [88], matured cat oocytes were vitrified in straws and, after IVF with frozen–thawed epididymal spermatozoa, the first two blastocysts were obtained [80]. In a recent study, the first attached cat blastocysts were obtained from matured cat oocytes that were vitrified using a cryo-loop system [89]. Another very recent study reported blastocyst production from vitrified germinal vescicle (GV) cat oocytes exposed to resveratrol (Res) in order to compact the decondensed chromatin contained in the large GV of cat oocytes [90]. Despite the importance of cryoprotectant penetration to avoid intracellular ice crystal formation, the greater cryoprotectant concentrations in vitrification solutions are toxic and may cause osmotic injury [91]. Suggestions for minimizing the toxicity of vitrification solutions include the use of less toxic substances, association with different cryoprotectants, previous exposure to lesser concentrations of cryoprotectants, and reduction of exposure time to vitrification solutions [92, 93]. The major penetrating cryoprotectants for oocyte cryopreservation are ethylene glycol (EG), glycerol (GLY), dimethylsulfoxide (Me2SO), propylene glycol (PrOH), and acetamide [94]. Another common permeating CPA, 1,2-ethanediol (EG) [94], is also suitable for less permeable immature oocytes, as demonstrated in cattle [95]. A recent study investigating bovine oocyte vitrification demonstrated that a solution of EG + Me2SO is a favorable cryoprotectant combination, as the Me2SO (MW = 78.13) molecule is smaller and consequently more permeable than the glycerol molecule (MW = 92.1) [96]. In our laboratory for the first time we obtained blastocysts from egg vitrified at GV stage from cat [97]. The vitrification was performed in OPS into sucrose medium (1 M sucrose in HSOF + 6% BSA) containing dimethyl sulfoxide (DMSO) (16.5% final concentration) and ethylene glycol (EG) (16.5% final concentration) as cryoprotectants. This vitrification protocol ensured a development to blastocyst stage and it is the first report of development of vitrified GV COC and confirmed that the selection of an appropriate cryoprotectant mixture and sample volume reduction are two simple but important parameters in the study of a successful vitrification method for feline species. Ovarian tissue cryopreservation combined with the subsequent transplantation into immunocompromised recipients, in order to resuming follicular development, is considered to be a promising approach for cryobanking female gametes in nondomestic felid species [81].
8. In vitro embryo production in felids
Several laboratories have independently assessed the potential of maturing and fertilizing domestic cat oocytes, mainly using IVM /IVF. The biological competency of IVM/IVF domestic cat embryos has been demonstrated after embryo transfer. Nonetheless, it has become apparent that IVM/IVF success in the cat is generally less than that reported for other commonly studied species like the cow [4]. For example, it is not unusual for 60–80% of cow antral follicular oocytes to be fertilized and to cleave in vitro [9]. Techniques in the mouse have progressed even further to allow the growth, maturation, and successful fertilization of oocytes from primordial ovarian follicles. In contrast, only about 50–60% of cultured cat oocytes achieve nuclear maturation in culture and, after insemination, usually <40% oocytes are fertilized on the basis of embryo cleavage [9]. Even under optimal culture conditions, <20% of these cleaved embryos grow into blastocysts
9. Artificial Insemination (AI) and Embryo Transfer (ET) in felids
Embryo transfer (ET) and artificial insemination (AI) are potentially important techniques for the propagation and management of genetically valuable domestic cat and endangered nondomestic cat populations. There are different AI techniques for cats [101]. In early studies, intravaginal insemination was exploited, but the success rate has not exceeded 43%. Later, this technique has been used with more effectiveness and a better success rate [102]. Another approach is intrauterine insemination, either surgical [103] or nonsurgical with the use of specially designed catheters [104]. They performed the first transcervical insemination with fresh or frozen semen in cats. This can be considered the method of choice in almost all cases; it is less invasive than the surgical approach, and a much smaller amount of semen is needed with respect to the intravaginal insemination. Recently, AI with semen cryopreservation has been applied in a number of wild felid species. Unfortunately, the teratospermia problem aggravates freezing/cryopreservation in many felid species [4]. In vitro embryo production has also been successful in felids. In vitro-derived embryos of the domestic cat were successfully frozen and developed to term kittens after cryopreservation and transfer. Various aspects of in vitro maturation of felid oocytes and in vitro culture of felid embryos have been comprehensively reviewed [4]. In 1979, the first successful embryo transfer (ET) in cats was reported [105]. The embryos, recovered from donors after mating during a natural cycle, were transferred into like recipients. Three litters of kittens were born from four pregnancies established in seven recipients. Nonetheless, in the following decade, in most ensuing reports on ET of in vitro-produced cat embryos, mixed morale and early blastocysts were deposited into the uterus of Day 4, 5, or 6 recipients [106-108]. This interval was used because it is the approximate length of time required for cat embryos to be transported through the oviduct and enter the uterus [109, 110]. To examine the effect of developmental stage, morula versus blastocyst, on pregnancy rate after ET, [111] recovered 1–4-cell embryos from gonadotropin-treated donors and cultured them in vitro (in 20% fetal calf serum) for 3–7 days before transfer into synchronous recipients. All four recipients of morulae (6–12 each) established pregnancies; two aborted before term, and two delivered a total of 10 kittens. Three of five recipients of blastocysts cultured for 4–6 days delivered a total of nine kittens, but none of the three recipients of blastocysts cultured for 7 days became pregnant. Although the zonal status of the blastocysts transferred after 7 days in vitro was not provided, most morulae had developed to the blastocyst stage by Day 7 of culture, with hatching starting to occur on Day 6 in blastocysts that were not fully expanded, which would suggest that most were either hatching or hatched when transferred. In their comments on failure of later-stage blastocysts (Day 8, 1 day in vivo, and 7 days in vitro) to establish pregnancies, the authors noted that further studies were needed “on in vivo development and hatching of transplanted embryos.” [112] found that separate transfer of in vitro-produced Day 5 late morulae and Day 5 early blastocysts into synchronous gonadotropin-treated recipients resulted in equally high pregnancy rates of 71% (5/7) and 80% (8/10), respectively. Each recipient received six morulae or six blastocysts and the average litter size was 2.0 (1–3) and 3.0 (1–3), respectively. Possibly, the only pregnancy/birth after ET of in vitro-derived (IVM/IVF/IVC) Day 7 blastocysts is the single kitten born from 21 embryos transferred into two synchronous recipients [113]. All of the blastocysts were completely zona-intact when transferred. The transfer of fresh or frozen in vitro-derived embryos has proved to be successful in some wildlife felids. In the lion (
10. Cloning of domestic and wild cats and interspecies of felide
Along with these achievements with cryobanking, the domestic cat has been cloned by two independent groups [114,115]. Recently, a domestic cat recipient female has been reported to have given birth to African wildcat (
11. Laparoscopic oviductal embryo transfer and artificial insemination in felids
The application of laparoscopy to reproductive studies in felids has been invaluable for helping to alleviate some concerns of animal welfare: sowing reproductive organs through the intraabdominal access through a minimally invasive and traumatic approach [116]. Likely, the extrapolation of ART to the genetic management of wild cats would be unattainable in the future without laparoscopy. The latter, for oocyte collection and intrauterine insemination, has been used largely with numerous cat species over the past 20 years. Recently, laparoscopic approaches have been developed and applied in cats for accessing the oviduct precisely to perform laparoscopic oviductal embryo transfer (LO-ET) and artificial insemination (LO-AI) procedures [117,118]. To our knowledge, just in eight cat hereditary disease models and two nondomestic cat species, the ocelot and sand cat, it has been possible to get viable offspring following LO-ET of nonfrozen and frozen–thawed IVF-derived embryos. LO-AI with low sperm numbers and LO-ET have been demonstrated to be similar in efficacy, resulting in high pregnancy percentages (50–70%) following insemination of domestic cats treated with gonadotrophins. Following LO-AI, multiple kittens have been produced in some hereditary disease models with frozen semen, and both Pallas’ cat and ocelot kittens were born after LO-AI with freshly collected semen. The application of LO-ET and LO-AI to felids has brought important and effective improvement in the efficiency of ART for genetic management of these invaluable wild and domestic cat populations [119].
12. Conclusions
In the present chapter, we made an overview of the data and methods detectable in literature and focused our attention on analysis of methods utilized in ART for maximizing their efficiency in feline species. ART include mainly Artificial Insemination (AI);
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