Reproduction in foxes: current research and future challenges

Comparative studies on ovary and serum hormone levels in silver and blue foxes and their hybrids

The silver and blue fox appear closely related despite their belonging to different genera, and the male and female fox hybrids are completely sterile in mating inter se or back to either of the parental groups. In the present study, we compared ovarian morphology and serum hormone concentrations among silver foxes, blue foxes, HSBs (silver fox male × blue fox female hybrids) and HBSs (blue fox male × silver fox female hybrids) during the pre-breeding and the breeding period. We found that either the fertile blue and silver foxes or the infertile hybrid foxes showed typical characteristics of ovary, with primordial, primary, secondary, antral and Graafian follicles. The diameters and quantities of different follicle classes in fertile foxes were greater than that in hybrids during the two period, while the thickness of zona pellucida (ZP) represented an opposite trend (P < 0.05). The relative weight of bilateral ovaries in fertile foxes was greater than that in hybrids during the pre-breeding period, while mean serum FSH represented an opposite trend during the breeding period (P < 0.05). The mean serum estradiol in fertile foxes was greater than that in HBS foxes during the pre-breeding period, and greater than hybrids during the breeding period (P < 0.05). These findings indicated that in the infertile hybrid foxes, lower estradiol levels produced by lesser and smaller antral follicles, thicker ZP during the two period, higher FSH levels during the breeding period, could be the basis of interpretations in cases of female fox hybrid infertility.

Canid Reproductive Biology: Norm and Unique Aspects in Strategies and Mechanisms

The reproductive physiology of canids is unique compared to other mammalian species. Specifically, the reproductive cycle of female canids is characterized by extended periods of proestrus and estrus followed by obligatory diestrus and protracted ovarian inactivity (anestrus). Although canid reproduction follows this general pattern, studies have shown variations in reproductive biology among species and geographic regions. Understanding of these differences is critical to the development of assisted reproductive technologies including estrus induction, gamete rescue, and embryo production techniques for canid conservation efforts. This review summarizes current knowledge of canid reproduction, including estrus cyclicity, seasonality, and seminal traits, with the emphasis on species diversity. The application of reproductive technologies in wild canid conservation will also be discussed.

Morphometric Characteristics of the Spermatozoa of Blue Fox (Alopex lagopus) and Silver Fox (Vulpes vulpes)

Simple Summary

The present study describes a detailed morphometric analysis of the sperm of the blue fox (Alopex lagopus) and silver fox (Vulpes vulpes), together with determination of the shape indices of the sperm head. Staining with silver nitrate enables precise identification of the acrosome and reveals structural details of the sperm tail, so that they can be accurately measured. Statistically significant differences were found for most of the morphometric parameters of the two fox species. The blue fox sperm were generally larger, but the acrosome area and coverage were greater in the silver fox. There are no clear recommendations regarding sperm staining techniques for foxes, and no reference values for morphometric parameters of the sperm of foxes or for canines in general. Staining with silver nitrate for evaluation of the morphometry of fox sperm can be used as an independent technique or an auxiliary technique in routine analysis of canine semen.

Abstract

The results presented in this study are the first such extensive characterization of the sperm morphometry of the blue fox (Alopex lagopus) and silver fox (Vulpes vulpes), as representatives of the family Canidae. Canine spermatozoa, especially the sperm of farmed foxes, are not often described in studies on reproduction. The aim of the study was a detailed comparison of the morphometric dimensions and shape of the sperm of two fox species: silver fox and blue fox. Semen collected from 10 silver foxes and 10 blue foxes was used for the study. The specimens were stained with silver nitrate. Measurements were performed of the length, width, perimeter, and area of the head; the area of the acrosome and its coverage; the length of the midpiece and its coverage; the length of the tail; and the length of the end piece of the tail. In addition, four head shape indices were calculated: ellipticity, elongation, roughness and regularity. The following values for the morphometric parameters and shape indices were obtained for blue fox and silver fox, respectively: head length—6.72 µm and 6.33 µm; head width—4.54.µm and 4.21 µm; head perimeter—18.11 µm and 17.37 µm; head area—21.94 µm² and 21.11 µm²; acrosome area—11.50 µm² and 10.92 µm²; midpiece length—12.85 µm and 12.79 µm; tail end piece length—3.44 µm and 3.28 µm; tail length—65.23 µm and 65.09 µm; acrosome coverage—52.43% and 52.83%; midpiece coverage—19.71% and 19.65%; sperm length—71.95 µm and 71.42 µm; ellipticity—1.49 and 1.52; elongation—0.19 and 0.20; roughness—0.84 and 1.88; regularity—1.09 and 0.99. The significance of differences between species was verified by Tukey’s test at p ≤ 0.05. Statistically significant differences between species were found for the following parameters: head length, width, perimeter and area; acrosome area; tail, end piece, and total sperm length; roughness and regularity. The differences in the size and shape of sperm can be used to establish reference patterns for fox sperm enabling more accurate species identification.

Breeding Profiles at the Periparturient Stage in Captive Red Foxes (Vulpes Vulpes) Mating Naturally or Subjected to Artificial Insemination in Japan

Introduction

Breeding profiles at the periparturient stage in red foxes which mated naturally or were subjected to artificial insemination were retrospectively surveyed using 130 vixens during their reproductive seasons of 2012–2017 in Japan.

Material and Methods

Natural mating vixens were encouraged a maximum of three times with the same male, while artificial insemination was conducted using frozen-thawed semen with the bovine semen extender as a diluent.

Results

With natural mating, conception rates after one, two, and three copulations were 55.8%, 68.0%, and 85.7%, respectively, showing a significant difference between the rates for one and three copulations. Conception rates with artificial insemination were 82.4%. Mean gestation periods were between 52.1 and 53.3 days in all groups. Mean litter sizes were 3.7–4.3 cubs with natural mating, and 4.4 cubs with artificial insemination. Although some sporadic and inconsistent changes in litter sizes were noted between primiparous and multiparous groups, these were of doubtful clinical importance.

Conclusion

This is the first report from Japan concerning basic breeding events of red fox vixens in captivity.

Collection and frozen storage of semen for artificial insemination in red foxes (Vulpes vulpes)

This study was conducted on red foxes to determine the appropriate voltage in electroejaculation for semen collection from stud males, and to confirm whether frozen semen with bovine semen extender can be used for artificial insemination. The proper load voltage for electroejaculation was 3-4 V based on semen collection rates and concentrations of spermatozoa. Frozen semen was prepared according to the known procedure for cows. In frozen-thawed semen, a relatively high conception rate (81.3%) was obtained in vixens, in which the optimum insemination time was detected by vaginal electrical resistance. These findings demonstrate that the restricted condition for semen collection by electroejaculation with cryopreservation of semen using bovine semen extender can be applied to artificial insemination of red foxes.

Sperm kinematic, head morphometric and kinetic-morphometric subpopulations in the blue fox (Alopex lagopus)

This work provides information on the blue fox ejaculated sperm quality needed for seminal dose calculations. Twenty semen samples, obtained by masturbation, were analyzed for kinematic and morphometric parameters by using CASA-Mot and CASA-Morph system and principal component (PC) analysis. For motility, eight kinematic parameters were evaluated, which were reduced to PC1, related to linear variables, and PC2, related to oscillatory movement. The whole population was divided into three independent subpopulations: SP1, fast cells with linear movement; SP2, slow cells and nonoscillatory motility; and SP3, medium speed cells and oscillatory movement. In almost all cases, the subpopulation distribution by animal was significantly different. Head morphology analysis generated four size and four shape parameters, which were reduced to PC1, related to size, and PC2, related to shape of the cells. Three morphometric subpopulations existed: SP1: large oval cells; SP2: medium size elongated cells; and SP3: small and short cells. The subpopulation distribution differed between animals. Combining the kinematic and morphometric datasets produced PC1, related to morphometric parameters, and PC2, related to kinematics, which generated four sperm subpopulations – SP1: high oscillatory motility, large and short heads; SP2: medium velocity with small and short heads; SP3: slow motion small and elongated cells; and SP4: high linear speed and large elongated cells. Subpopulation distribution was different in all animals. The establishment of sperm subpopulations from kinematic, morphometric, and combined variables not only improves the well-defined fox semen characteristics and offers a good conceptual basis for fertility and sperm preservation techniques in this species, but also opens the door to use this approach in other species, included humans.

Quality of fresh and chilled-stored raccoon dog semen and its impact on artificial insemination efficiency

Background

The aim of the study was to evaluate the quality of fresh raccoon dog semen and raccoon dog semen stored at 4 °C. The qualitative evaluation was based on apoptosis in the sperm cells, which was tested by the Annexin V/Pi assay, the TUNEL method and JC-1. In addition, the suitability of the semen for insemination and its effect on reproduction in females were determined in relation to the time of storage.

Results

During cold storage of the semen, in the samples from all groups a gradual decrease was noted in the percentage of live cells, and an increase in the percentage of cells with abnormal morphology, exhibiting changes typical of late-stage apoptosis (V⁺/PI⁺), and of necrotic cells (V⁻/PI⁺). There was a significant increase in the percentage of ApoBrDu + sperm cells, while the mitochondrial membrane potential of the sperm decreased significantly after 12 h of storage at 4 °C in the case of lower-quality semen and after 48 h in the case of semen of good quality. As the percentage of sperm with DNA and cell membrane damage increased and the mitochondrial membrane potential decreased, there was an increase in AspAT and acrosin activity. The increase in the percentage of apoptotic sperm in the raccoon dog semen stored at 4 °C resulted in a decrease in the number of females with cubs.

Conclusions

Identification of apoptotic changes in sperm by flow cytometry using the annexin assay, the TUNEL assay and evaluation of mitochondrial membrane potential can be recommended for determination of the suitability of raccoon dog semen for artificial insemination. The study shows that fresh raccoon dog semen should not be used for insemination more than 48 h after collection in the case of semen of very high quality, or after more than 24 h in the case of semen of poorer quality. Cytometric methods of semen analysis should also be used to evaluate various extenders of raccoon dog semen and methods of cryopreservation in terms of ensuring sperm viability, fertilization capacity, and suitability for insemination.

Reproductive and pituitary-adrenal axis parameters in normal and prenatally stressed prepubertal blue foxes (Alopex lagopus)

Man-animal relationships are involved in the process of fox domestication. Handling being an important part of man-animal contacts, causes stress responses in farm-bred blue foxes. The purpose of this study was to determine how prenatal stress induced by handling pregnant vixens influences certain morphometric and hormonal parameters of adrenocortical and gonadal function in the prepubertal offspring. Blue fox females were subjected to daily handling sessions, each of 1 min, in the last trimester of pregnancy (term = 52 days). Plasma concentrations of ACTH, cortisol, progesterone, oestradiol and testosterone, as well as the in vitro adrenal and gonadal production of steroids were measured by radio-immunoassay in control (C, no. = 56) and prenatally stressed (PS, no. = 56) blue fox cubs of both sexes at the age of 6 to 7 months. Prenatal stress decreased plasma concentration of cortisol (C: 31·0 (s.e. 4·3) v. PS: 22·7(s.e. 1·6) ng/ml, P < 0·05) as well as progesterone (C: 1·00(s.e. 0·10) v. PS: 0·65(s.e. 0·05) ng/ml, P < 0·05) in female cubs. Prenatal stress did not cause any changes in adrenal or gonadal weights, plasma concentrations of testosterone or oestradiol, or in vitro adrenal or gonadal steroid production, in either sex. It is concluded that persistent handling of pregnant blue foxes did not affect the prepubertal development of the reproductive system but resulted in disregulation in the hypothalamic-pituitary-adrenal axis in the female offspring.

Role of Membrane Lipid Fatty Acids in Sperm Cryopreservation

Lipid is an important constituent of cell membrane. Membrane lipid composition of spermatozoa has been correlated to different function. Many researchers have related membrane lipid with survival success after cryopreservation or cold shock. Sperm maturation and acrosome reactions are natural phenomenon, but cryopreservation or cold shock is not. Therefore, sperm cells are not programmed for such change and undergo stress. So the change in membrane lipid composition due to cold shock or cryopreservation may be looked upon as response of spermatozoa to a certain stressed condition. A significant body of research worked on the relationship between membrane lipid and fatty acid composition and ability of cell to tolerate adverse change in temperature. However, as the approach of different research groups was different, it is very difficult to compare the changes. Studies have been done with different species, ejaculated/seminal or epididymal sperm. Lipid analyses have been done with whole cell membrane isolated by different methods. Fatty acids estimated were from whole cell, plasma membrane, head membrane, or phospholipids. The cryopreservation condition, media composition, and diluents/cryoprotectants were also different. At this onset a comprehensive review is needed to cover changes of sperm membrane lipid composition of different species under different cryopreservation conditions.

Flow cytometric evaluation of sperm apoptosis in semen of silver foxes in the breeding period

The objective of the study was to evaluate cytometrically the percentage of apoptotic and necrotic spermatozoa in fresh semen of silver foxes in the breeding season. In males F3 and F4 with high percentages of early apoptotic (A+Pi-), late apoptotic (A+Pi+) and necrotic (A-Pi+) spermatozoa as well as 56-65% of living spermatozoa (A-Pi-) with progressive motility, the semen was characterised by reduced fertility. In males F1 and F2 with spermatozoa showing the motility and viability of 89-90% and high percentages of living cells that do not bind Annexin V and propidium iodide, the semen was assessed as valuable and useful for artificial insemination. Amongst 16 females of group I and II inseminated with semen from F1 and F2 males, 15 (93.75%) had multi-cub litters - on average 6.1 and 4.8, respectively. In contrast, amongst 16 females of group III and IV inseminated with semen from F3 and F4 males, only 10 (62.5%) had litters with few cubs (on average 2.6 in group III and 2.1 in group IV). Our findings explicitly indicate that semen of farm male foxes should be evaluated before the breeding season, as one of the causes of reproduction failures is likely to be a high percentage of apoptotic and necrotic spermatozoa. Thanks to flow cytometry, fresh ejaculates can be speedily evaluated and their usefulness for artificial insemination determined.

Canid progesterone receptors lack activation function 3 domain-dependent activity

Progesterone regulates multiple behavioral, physiological, and pathological aspects of female reproductive biology through its two progesterone receptors (PRs), PR-B and the truncated PR-A. PR-B is necessary for mammary gland development in mice and, compared with PR-A, is overall a stronger transactivator of target genes due to an additional activation function 3 (AF3) domain. In dogs, known for their high sensitivity to progesterone-induced mammary cancer, the PR-B function was studied. Canine PR (cPR)-B appeared to contain multiple mutations within AF3 core sequence motifs and lacks N-terminal ligand-independent posttranslational modifications. Consequently, cPR-B has a weak transactivation potential on progesterone-responsive mouse mammary tumor virus-luc and progesterone response element 2-luc reporters transiently transfected in hamster, human, or canine cells and also on known target genes FKBP5 and SGK in doxycycline-inducible, stable transfected cPR-B in canine mammary cells. The cPR-B function was restored to the level of human PR-B by the replacement of canine AF3 domain with the human one. The lack of AF3 domain-dependent transcriptional activity was unique for canids (gray wolf, red fox, and raccoon dog) and not present in closely related caniform species (brown bear, gray seal, and domestic ferret). Despite the limited transactivation potential, canids develop normal mammary glands and frequently mammary tumors. Therefore, these results question the role of PR-B in breast cancer development and may explain unique features of canid reproduction.

The effect of a combination of permanent breeding cage and low housing density on the reproductive success of farmed blue foxes

Social factors are known to affect the reproduction of many canids both in the wild and in farms. For example, reproduction in farmed silver foxes is regulated by social stress; foxes seem to benefit from noncramped housing conditions and permanent breeding cages. However, no comparable studies have been carried out in farmed blue foxes. The aim of our experiment was to create an alternative, improved, economically viable and practical housing solution for blue foxes. Therefore, we compared reproductive performance of blue foxes in permanent breeding cages with low animal densities (L group, N=79) and traditional housing with its changing social environment with high animal density (H group, N=74). The reproductive data from the L and H groups were compared separately for primiparous and multiparous vixens because the reproductive performance in primiparous vixens was substantially lower (P<0.001) than in multiparous vixens. Altogether, 41 and 39% of the primiparous vixens in the H and L group whelped (P>0.05), but only 28 and 34%, respectively, weaned at least one cub (P>0.05), i.e., 72 and 66% of the primiparous vixens did not reproduce in the H and L group, respectively (P>0.05). The total reproductive performance, expressed as cubs at weaning per breeding female, was 1.7+/-3.5 for the H and 1.6+/-2.9 for the L group (P>0.05). In the primiparous vixens, the only statistically significant difference observed between the two housing systems was that the onset of oestrus occurred five days earlier in the H than in the L group (P<0.05). All multiparous vixens in the L group exhibited oestrus compared to 94% in the H group (P>0.05). Furthermore, there was a nonsignificant (ns) trend for fewer barren females (9% versus 17%), more successfully reproducing vixens (83% versus 74%) and a higher number of live-born cubs (10.9+/-4.7 versus 9.4+/-3.9) in the L than in H group in the multiparous vixens (for all P>0.05). This resulted in 1.7 and 1.4 cubs more per breeding and per mated vixen, respectively, at weaning in the L group (7.3+/-5.0) compared to the H group (5.6+/-4.2), but also this difference was nonsignificant. Although our present results lack statistical significance, they are promising enough to encourage field experiments with sufficiently large number of animals to prove or disprove these preliminary findings that lower housing density and permanent breeding cage, together or separately, may enhance reproduction particularly in multiparous blue fox vixens.

Comparative aspects of sperm membrane fatty acid composition in silver (Vulpes vulpes) and blue (Alopex lagopus) foxes, and their relationship to cell cryopreservation

Cryogenic protocols have been developed for the storage of farmed silver fox (Vulpes vulpes) spermatozoa. However, these same protocols and modifications of these protocols have failed to satisfactorily preserve spermatozoa collected from farmed blue foxes (Alopex lagopus). Because cryogenic success has been linked to membrane composition, the plasma membrane lipid composition of farmed blue fox and silver fox spermatozoa was studied. Silver fox spermatozoal membranes have significantly higher levels of docosapentaenoic acid (DPA; 22:5, n-6) compared to blue fox spermatozoa, and blue fox spermatozoal membranes have significantly higher levels of stearic acid (18:0). Silver fox spermatozoal membranes not only have a higher ratio of unsaturated/saturated membrane fatty acids, but also higher levels of membrane desmosterol and cholesterol.

Non-invasive faecal steroid monitoring of ovarian and adrenal activity in farmed blue fox (Alopex lagopus) females during late pregnancy, parturition and lactation onset

In the semi-domesticated blue fox, handling stress may influence reproductive performance and increase perinatal pup loss. Ovarian and adrenal steroids were analysed in faecal samples collected from mid-gestation through the first week of lactation in 40 female blue foxes to characterize hormone patterns during this important reproductive period. Daily faecal samples were collected from 40 foxes during 30 pregnancies, one late abortion and nine bred-matched non-pregnancies. Mean concentrations of faecal progestagens over the 10 days before birth were significantly higher in pregnant compared to non-pregnant females (51+/-1.50 microg/g versus 36+/-3.72 microg/g, respectively; P < 0.01). From 10 to 3 days before whelping, total faecal oestrogen concentrations also were higher (P < 0.01) in pregnant (1082+/-41.69 ng/g) than non-pregnant (628+/-72.43 ng/g) foxes, before declining to non-pregnant values (402+/-24.88 ng/g) after parturition. Overall mean faecal corticoid concentrations from 3 to 20 days before whelping differed between pregnant and non-pregnant foxes (128+/-3.11 ng/g versus 103+/-5.86 ng/g, respectively; P < 0.01). Furthermore, in pregnant foxes, corticoid excretion increased further from 2 days before to 3 days after whelping (216+/-13.71 ng/g; P < 0.01). Thereafter, corticoid concentrations were similar between pregnant and non-pregnant females (P > 0.05). In sum, the faecal steroid hormone patterns for oestrogens and progestagens were similar to those previously obtained by analyses of fox serum hormones, with both steroids being higher in pregnant than non-pregnant foxes at the end of gestation. The elevation in corticoid concentrations in pregnant females suggests that adrenal activation is involved in the initiation of parturition in the blue fox. Thus, faecal steroid analyses can be used to monitor ovarian activity during pregnancy and pseudopregnancy in farmed blue fox females.

Studies on vertical transmission of Trichinella spp. in experimentally infected ferrets (Mustela putorius furo), foxes (Vulpes vulpes), pigs, guinea pigs and mice

Vertical transmission of Trichinella spiralis was evaluated in ferrets (n=21), foxes (n=11), pigs (n=12), guinea pigs (n=16), and mice (n=41). The placental barrier to be crossed by migratory Trichinella larvae varies structurally in different animal species. Ferrets and foxes have an endotheliochorial placenta structure, guinea pigs and mice a haemochorial, and pigs an epitheliochorial placenta. The non-encapsulating Trichinella pseudospiralis larvae have an extended muscle migration prior to entering a muscle cell. To evaluate if T. pseudospiralis was more likely to be transmitted to offspring, an additional group of foxes (n=11) infected with T. pseudospiralis was included. Two different dose levels were used for ferrets, pigs, guinea pigs, and mice. In pigs and guinea pigs, infection was given at different times of the gestation period. Vertical transmission, measured as recovery of muscle larvae in the offspring, was demonstrated in both ferrets groups, in all four guinea pig groups, and in the high dose mouse group, but not in any fox or pig groups.

New commercial opportunities for advanced reproductive technologies in horses, wildlife, and companion animals

As advanced reproductive technologies become more efficient and repeatable in livestock and laboratory species, new opportunities will evolve to apply these techniques to alternative and non-traditional species. This will result in new markets requiring unique business models that address issues of animal welfare and consumer acceptance on a much different level than the livestock sector. Advanced reproductive technologies and genetic engineering will be applied to each species in innovative ways to provide breeders more alternatives for the preservation and propagation of elite animals in each sector. The commercialization of advanced reproductive techniques in these niche markets should be considered a useful tool for conservation of genetic material from endangered or unique animals as well as production of biomedical models of human disease.

Cryopreservation of gametes and embryos of non-domestic species

Many species of mammals are threatened or endangered. Methods of assisted reproduction that are being used with increasing frequency to produce offspring of domestic animals and humans are often viewed as offering innovative ways to reproduce non-domestic species as well. Uncounted millions of live young of domestic or laboratory species have been produced from gametes and embryos stored at -70 degrees C or below, sometimes for as long as 25 to 35 yrs. Such methods of cryopreservation are now being applied with increasing frequency and urgency to preserve gametes and embryos of non-domestic and threatened species to establish "genome resource banks" or "frozen zoos." But levels of success to produce live young from such cryopreserved gametes or embryos vary considerably from species to species, as well as from individual to individual. It is sometimes thought that differences among species in fundamental characteristics of their gametes may determine the efficacy of cryopreservation and the production of live young. However, it may not be that ineffective cryopreservation is responsible for low success rates. Rather, the limiting factor may be insufficient information and knowledge of the most basic reproductive biology of such non-domestic species. Even standard methods of cryopreservation may be completely adequate to act as a "temporary" expedient to preserve germplasm of non-domestic species to permit time to acquire a fuller understanding of the biology and behavior of non-domestic species.

Current state in biotechnology in canine and feline reproduction

Biotechnology has proceeded much further in cats than in canines, although the pregnancy rate after in vitro maturation (IVM), IVC and embryo transfer (ET) is still relatively low. The use of AI with frozen-thawed semen as a breeding tool to overcome breeding incompatibility or to preserve male genetic material has been limited in felines in contrast to the situation in domestic dogs and foxes. In many research scenarios and endangered felid species programs, the in vitro production of feline embryos with subsequent transfer has complemented the use of AI. Improvement of IVM, in vitro fertilization (IVF) and embryo culture coupled with ovarian tissue grafting, cryobanking of follicles, oocytes, semen, or embryos, with subsequent ET into surrogate females, may render this technology feasible for use in endangered wild felids. In canines, reliable systems for in vitro production of embryos, embryo cryopreservation and transfer are yet to be developed. The refinement of invasive fertilization techniques, such as intracytoplasmic sperm injection (ICSI), may eventually provide a tool for removal of recipient oocyte nuclei and transfer of selected embryonic or somatic cell donor nuclei into domestic cat ooplasm, thereby providing a tool for genetic modification, or for preservation of valuable genetic material.

Reproductive management of silver foxes (Vulpes vulpes) in captivity

Specific protocols need to be developed that take into consideration the requirements of silver foxes. This study was designed to investigate the reproduction of 26 pairs of silver foxes (Vulpes vulpes). Reproduction parameters (breeding season, age at puberty, fecundity and fertility) of the foxes were examined under experimental conditions, and new techniques to optimize fox breeding were assessed. Staining of the vaginal smears with the double Harris-Schorr stain allowed for the precise detection of estrus and proved to be more reliable than simply measuring vaginal resistance. Ultrasonography was demonstrated to be useful for pregnancy diagnosis and prediction of parturition. Results demonstrate that the methods reported in this paper are easily applicable to similar studies carried out on small groups of animals within the framework of fox animal experimentation.