Macroscopic and roentgenographic anatomy of the skull of the ferret (Mustela putorius furo)

Normal macroscopic and roentgenographic features of the skull of the ferret (Mustela putorius furo) were examined and described. Data were based on a sample of 100 (50 male and 50 female) adult ferrets of known body weight and age. The skull was described macroscopically according to six standard views, i.e. dorsal, lateral, ventral, caudal, cranial and midsagittal. The mandible was described separately. The roentgenographic characteristics of the ferret skull were demonstrated only in lateral and dorsoventral projections. Furthermore, the skull length and width as well as the minimum frontal width were measured, and skull indices were derived from relevant measurements. Sexual dimorphism was examined both morphologically and craniometrically. Besides the common features of a carnivore skull, the ferret skull is relatively elongated and flat with a short facial region. The skulls of adult male ferrets are about 17% longer and 22% wider than those of the females. Significant sexual dimorphism also exists regarding certain skull indices. The general features and some dimensional parameters of the adult ferret skull support the contention that the ferret would be an interesting and workable alternative animal model in craniofacial research.     

Comparison of black-footed ferret (Mustela nigripes) and domestic ferret (M. putorius furo) courtship activity

Because of the scarcity of the endangered black-footed ferret (Mustela nigripes) and the amount of knowledge necessary for their conservation, surrogate research can play an important role in recovery. In this paper, we investigate surrogate behavioral research potential by comparing courtship behavior of the black-footed ferret to the congeneric domestic ferret (M. putorius furo). Ten female domestic ferrets were bred to five male domestic ferrets and eight female black-footed ferrets were bred to five black-footed ferret males. Courtship activities were defined, analyzed, and quantitatively compared between both groups. Lag sequential analysis of was used to prepare the behavioral matrices, and matrix cells were compared between groups with an equality of proportions test. Courtship patterns did not differ significantly between the two closely related species, and the domestic ferret would probably be an adequate surrogate for reproductive behavior research on the black-footed ferret.     

The ferret: an animal model to study influenza virus

There has been much critical influenza research conducted in a little-known laboratory animal--the ferret. The authors review some of these findings, discuss the reasons the ferret often becomes a model for influenza infection, and compare the ferret with other animal models.     

The ferret as a model organism to study influenza A virus infection

Influenza is a human pathogen that continues to pose a public health threat. The use of small mammalian models has become indispensable for understanding the virulence of influenza viruses. Among numerous species used in the laboratory setting, only the ferret model is equally well suited for studying both the pathogenicity and transmissibility of human and avian influenza viruses. Here, we compare the advantages and limitations of the mouse, ferret and guinea pig models for research with influenza A viruses, emphasizing the multifarious uses of the ferret in the assessment of influenza viruses with pandemic potential. Research performed in the ferret model has provided information, support and guidance for the public health response to influenza viruses in humans. We highlight the recent and emerging uses of this species in influenza virus research that are advancing our understanding of virus-host interactions.     

Geographic origin of journal articles on nonhuman primates

During the 1970s variations in the number of citations published in CURRENT PRIMATE REFERENCES seemed to parallel changes in the fortunes of primate research in the United States. In 1981 and 1982, however, the trends diverged, with the number of citations increasing 25% over the two years. In an effort to identify more specifically some factors underlying the trend in literature growth, citations of journal articles appearing in 1971, 1976, and 1981 issues were tabulated according to the general subject indicated by the title and the site of research indicated by the author's address. The number of journal articles was 20% larger in 1981 than in 1971. The United States was the largest contributor in all three years, but its relative contribution declined. Continental Western Europe ranked second consistently, and its contribution grew at an above-average rate. Japan ranked fifth in 1971 and third in 1981. India contributed less than 2% of the literature in 1971 and more than 3% in 1981, as a result of a doubling of its contribution. The subject composition of the literature did not change greatly.     

Dracunculus insignis: experimental infection in the ferret, Mustela putorius furo

The laboratory study of dracunculiasis has suffered from the lack of a suitable, readily available animal model. We have been able to experimentally infect ferrets. Mustela putorius furo, with the North American dracunculid, Dracunculus insignis. Ferrets were inoculated with 75 to 100 infective larvae and were necropsied 90 to 240 days later. Guinea worms were recovered from 10 (56%) of 18 ferrets. A total of 44 worms were recovered, for an average of 4.4 worms per infected ferret. Gravid female worms were recovered as early as 128 days postinoculation. Thirteen (87%) of 15 gravid female worms were recovered from the extremities. Living male worms were recovered at 200 days of age, indicating that not all male worms die shortly after mating. First-stage larvae recovered from gravid females as early as 200 days of age were found to be infective to the copepod, Acanthocyclops vernalis. These observations suggest that the ferret is an excellent laboratory animal for dracunculiasis research.     

Incorrect Citations Give Unfair Credit to Review Authors in Ecology Journals

The number of citations that papers receive has become significant in measuring researchers'' scientific productivity, and such measurements are important when one seeks career opportunities and research funding. Skewed citation practices can thus have profound effects on academic careers. We investigated (i) how frequently authors misinterpret original information and (ii) how frequently authors inappropriately cite reviews instead of the articles upon which the reviews are based. To reach this aim, we carried a survey of ecology journals indexed in the Web of Science and assessed the appropriateness of citations of review papers. Reviews were significantly more often cited than regular articles. In addition, 22% of citations were inaccurate, and another 15% unfairly gave credit to the review authors for other scientists'' ideas. These practices should be stopped, mainly through more open discussion among mentors, researchers and students.     

A Scoping Review of Published Research on the Relinquishment of Companion Animals

Globally, large populations of companion animals are relinquished each year. The purpose of this scoping review was to identify all published research investigating companion-animal relinquishment to map out and evaluate research gaps, needs, and opportunities. A comprehensive search strategy was implemented in 4 online databases, identified citations were screened, and relevant articles were procured and characterized. From 6,848 unique citations identified, 192 were confirmed relevant, including 115 primary-research articles and 77 reviews and commentaries. The majority of these articles originated from the United States (131; 68.2%); 74 (38.5%) of them have been published since 2006. Among the primary-research articles, 84 (73.0%) investigated reasons for companion-animal relinquishment. The most commonly studied reasons were aggressive companion-animal behaviors (49; 58.3%); moving, rental, or housing issues (45; 53.6%); and caretaker personal issues (42; 50.0%). Only 17 primary-research articles investigated interventions to prevent companion-animal relinquishment. The quantity of research into reasons for relinquishment highlights an opportunity for future knowledge-synthesis activities in this area, including systematic review and meta-analysis. In comparison, the limited research into interventions identifies a priority for new research.     

Anatomic and physiological characteristics of the ferret lateral rectus muscle and abducens nucleus.

The ferret has become a popular model for physiological and neurodevelopmental research in the visual system. We believed it important, therefore, to study extraocular whole muscle as well as single motor unit physiology in the ferret. Using extracellular stimulation, 62 individual motor units in the ferret abducens nucleus were evaluated for their contractile characteristics. Of these motor units, 56 innervated the lateral rectus (LR) muscle alone, while 6 were split between the LR and retractor bulbi (RB) muscle slips. In addition to individual motor units, the whole LR muscle was evaluated for twitch, tetanic peak force, and fatigue. The abducens nucleus motor units showed a twitch contraction time of 15.4 ms, a mean twitch tension of 30.2 mg, and an average fusion frequency of 154 Hz. Single-unit fatigue index averaged 0.634. Whole muscle twitch contraction time was 16.7 ms with a mean twitch tension of 3.32 g. The average fatigue index of whole muscle was 0.408. The abducens nucleus was examined with horseradish peroxidase conjugated with the subunit B of cholera toxin histochemistry and found to contain an average of 183 motoneurons. Samples of LR were found to contain an average of 4,687 fibers, indicating an LR innervation ratio of 25.6:1. Compared with cat and squirrel monkeys, the ferret LR motor units contract more slowly yet more powerfully. The functional visual requirements of the ferret may explain these fundamental differences.     

Pulmonary arterial and venous constriction during hypoxia in 3- to 5-wk-old and adult ferrets

We have determined the sites of hypoxic vasoconstriction in ferret lungs. Lungs of five 3- to 5-wk-old and five adult ferrets were isolated and perfused with blood. Blood flow was adjusted initially to keep pulmonary arterial pressure at 20 cmH2O and left atrial and airway pressures at 6 and 8 cmH2O, respectively (zone 3). Once adjusted, flow was kept constant throughout the experiment. In each lung, pressures were measured in subpleural 20- to 50-microns-diam arterioles and venules with the micropipette servo-nulling method during normoxia (PO2 approximately 100 Torr) and hypoxia (PO2 less than 50 Torr). In normoxic adult ferret lungs, approximately 40% of total vascular resistance was in arteries, approximately 40% was in microvessels, and approximately 20% was in veins. With hypoxia, the total arteriovenous pressure drop increased by 68%. Arterial and venous pressure drops increased by 92 and 132%, respectively, with no change in microvascular pressure drop. In 3- to 5-wk-old ferret lungs, the vascular pressure profile during normoxia and the response to hypoxia were similar to those in adult lungs. We conclude that, in ferret lungs, arterial and venous resistances increase equally during hypoxia, resulting in increased microvascular pressures for fluid filtration.     

Responses to innocuous, but not noxious, somatosensory stimulation by neurons in the ferret superior colliculus

The intermediate and deep layers of the superior colliculus (SC) are known for their role in initiating orienting behaviors. To direct these orienting functions, the SC of some animals (e.g., primates, carnivores) is dominated by inputs from the distance senses (vision, audition). In contrast, the rodent SC relies more heavily on non-visual inputs, such as touch and nociception, possibly as an adaptive response to the proximity of dangers encountered during their somatosensory-dominant search behaviors. The ferret (a carnivore) seems to employ strategies of both groups: above ground they use visual/auditory cues, but during subterranean hunting ferrets must rely on non-visual signals to direct orienting. Therefore, the present experiments sought to determine whether the sensory inputs to the ferret SC reveal adaptations common to functioning in both environments. The results showed that the ferret SC is dominated (63%; 181/286) by visual/auditory inputs (like the cat), rather than by somatosensory inputs (as found in rodents). Furthermore, tactile responses were driven primarily from hair-receptors (like cats), not from the vibrissae (as in rodents). Additionally, while a majority of collicular neurons in rodents respond to brief noxious stimulation, no such neurons were encountered in the ferret SC. A small proportion (4%; 13/286) of the ferret SC neurons were responsive to long-duration (>5 s) noxious stimulation, but further tests could not establish these responses as nociceptive. Collectively, these data indicate that the ferret SC is best adapted for the animal's visuallacoustically guided activities and most closely resembles the SC of its phylogenetic relative, the cat.     

A comparison of sperm morphology and silver nitrate staining characteristics in the domestic ferret and the black-footed ferret

Ejaculated sperm from the domestic ferret (Mustela putorius furo) and the black-footed ferret (Mustela nigripes) were compared for differences in morphological abnormalities and argentophilic protein distribution. Thawed domestic ferret sperm was also compared to fresh sperm to determine whether there were any effects on cell morphology due to cryopreservation. There were statistically significant differences between the two species of ferret in two of the categories scored. The domestic ferret had a higher frequency of cells that were bent in the midpiece and in the principal piece, and a higher frequency of headless and tailless cells when compared to the black-footed ferret. There were no statistically significant differences in cell morphology between the fresh and cryopreserved ejaculates of the domestic ferret employing a standard egg yolk cryoextender. Silver nitrate staining distribution was different between the two species in both the head and tail region.     

Issues to consider for preparing ferrets as research subjects in the laboratory

The domestic or European ferret (Mustela putorius furo) has been domesticated for thousands of years. Ferrets have been used for hunting and fur production, as pets, and as models in biomedical research. Despite the relatively small numbers used in the laboratory, ferrets have some unique applications including study of human influenza and severe acute respiratory syndrome (SARS)-associated corona virus. They have served as models for peptic ulcer disease, carotenoid metabolism, cystic fibrosis, and drug emesis screening, among others. Most research ferrets are males, due to estrus-related health problems in females. They may be housed conventionally and are easy to care for when their biology and behavior are understood. Due to the small number of ferret suppliers, animals are often shipped long distances, requiring air transport and intermediate handlers. It is important to minimize shipment stress, especially with weanling and pregnant animals. Additional expertise is required for success with pregnant and whelping ferrets and for rearing of neonates. The animals have specific dietary requirements, and proper nutrition is key. Successful housing requires knowledge of ferret behaviors including social behavior, eating habits, a general inquisitive nature, and a species-typical need to burrow and hide. Regular handling is necessary to maintain well-being. A ferret health care program consists of physical examination, immunization, clinical pathology, and a working knowledge of common ferret diseases. Various research methodologies have been described, from basic procedures such as blood collection to major invasive survival surgery. Ferrets have a distinct niche in biomedical research and are hardy animals that thrive well in the laboratory.     

Steroid metabolism in the corpus luteum of the ferret

Implantation in the ferret is believed to be induced by a luteal substance which acts in concert with progesterone (P4) and which is secreted sometime between Days 6 and 8 of pregnancy. This experiment was designed to identify the steroid products synthesized by ferret corpora lutea (CL) on these 2 days of pregnancy. CL were dissected from ferrets on Day 6 or 8 of pregnancy and incubated with [3H] pregnenolone (P3), [3H] P4, or [3H] dehydroepiandrosterone (DHEA). Controls with no tissue or with 50 microliters packed blood cells were incubated at the same time. After incubation of Day 6 CL with [3H] P3 for 180 min, 39% of the added label was found incorporated into P4, 3% into 17 alpha-hydroxyprogesterone (17 alpha-OHP4) and 1% into androstenedione (A). Incubation of Day 8 CL with the same precursor resulted in 35%, 1% and 0.65% of the label being incorporated into the previously mentioned products, respectively. Incubations of Days 6 and 8 ferret CL with [3H] P4 or [3H] DHEA confirmed these results, demonstrating activity of C21-steroid, 17 alpha-hydroxylase and delta 5-isomerase, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD). These results suggest that ferret CL primarily accumulate steroids of the delta4 pathway on both Days 6 and 8 of pregnancy, with P4, 17 alpha-OHP4, A and testosterone (T) being the most abundant products after in vitro incubation. Thus, ferret CL appear to metabolize steroids in a manner similar to that observed in rats, sows and mares.     

Responses to innocuous,but not noxious,somatosensory stimulation by neurons in the ferret superior colliculus

The intermediate and deep layers of the superior colliculus (SC) are known for their role in initiating orienting behaviors. To direct these orienting functions, the SC of some animals (e.g., primates, carnivores) is dominated by inputs from the distance senses (vision, audition). In contrast, the rodent SC relies more heavily on non-visual inputs, such as touch and nociception, possibly as an adaptive response to the proximity of dangers encountered during their somatosensory-dominant search behaviors. The ferret (a carnivore) seems to employ strategies of both groups: above ground they use visual/auditory cues, but during subterranean hunting ferrets must rely on non-visual signals to direct orienting. Therefore, the present experiments sought to determine whether the sensory inputs to the ferret SC reveal adaptations common to functioning in both environments. The results showed that the ferret SC is dominated (63%; 181/286) by visual/auditory inputs (like the cat), rather than by somatosensory inputs (as found in rodents). Furthermore, tactile responses were driven primarily from hair-receptors (like cats), not from the vibrissae (as in rodents). Additionally, while a majority of collicular neurons in rodents respond to brief noxious stimulation, no such neurons were encountered in the ferret SC. A small proportion (4%; 13/286) of the ferret SC neurons were responsive to long-duration (> 5s) noxious stimulation, but further tests could not establish these responses as nociceptive. Collectively, these data indicate that the ferret SC is best adapted for the animal's visual/acoustically guided activities and most closely resembles the SC of its phylogenetic relative, the cat.     

Factors affecting the electrofusion of mouse and ferret oocytes with ferret somatic cells

The domestic ferret, Mustela putorius furos, holds great promise as a genetic model for human lung disease, provided that key technologies for somatic cell nuclear transfer (SCNT) are developed. In this report, we extend our understanding of SCNT in this species by defining conditions for efficient cell fusion by electrical pulse. Two experimental systems were employed in this study. First, in vivo-matured mouse oocytes and ferret somatic cells were used to establish general parameters for fusion. One fibroblast, or cumulus cell, was agglutinated to nucleate, zona pellucida-free, mouse oocytes, and subjected to an electrical pulse. Similar electrical pulse conditions were also tested with 1 or 2 somatic cells inserted into the perivitelline space (PVS) of intact mouse oocytes. The fusion rate for a single fibroblast with a zona-free oocyte was 80.2%, significantly higher (P < 0.05) than that observed for 1, or 2, fibroblasts placed in the PVS (52.0% and 63.8%, respectively). The fusion rate (44.1%) following insertion of two cumulus cells was significantly higher (P < 0.05) than that following insertion of one cumulus cell (25.1%). Second, in vitro-matured ferret oocytes were enucleated, and one to three fibroblasts or cumulus cells were inserted into the PVS. Zona pellucida-free ferret oocytes were fragile and excluded from the study. The fusion rates with two or three fibroblasts were 71.4% and 76.8%, respectively; significantly higher (P < 0.05) than that for one fibroblast (48.6%). This cell number-dependent difference in fusion efficiency was also observed with cumulus cells. Fusion-derived (ferret-ferret) NT embryos cleaved, formed blastocysts in vitro, and underwent early-stage fetal development following embryo transfer. The rate of development was cell type-independent, in contrast to the cell type-dependent differences observed in fusion efficiency. In conclusion, fibroblasts fused more efficiently than cumulus cells and the efficiency of single cell fusions was improved when two or more cells were inserted into the PVS. These studies define conditions for efficient cell fusion with ferret oocytes and should facilitate SCNT and the development of genetically defined animal models in this species.     

Behavior and neurobehavioral teratology using the ferret

A behavioral profile of the ferret is presented for those who would like to use this animal in behavioral teratology and toxicology, or other disciplines involving behavior. We have reviewed neurobehavioral teratology of lisencephalic ferrets and neuropsychology of ferrets sustaining frontal lesions, as well as most of the studies of "normal" ferret behavior that have appeared in the research literature. Emphasis is placed on discussion of the tests used and how ferrets behaved on them. The behaviors discussed include spatial (maze) learning, delayed response, visual discrimination learning, discrimination learning sets, schedule maintained behavior, shock avoidance learning and spontaneously occurring behaviors, such as ambulation in open field, spontaneous alternation and species specific behaviors. Although the use of the ferret in behavioral experiments is not yet extensive and large gaps exist in our knowledge about the basic functional capacities of this animal, the ferret is unquestionably well suited for behavioral studies.     

A test of mink microsatellite markers in the ferret: amplification and sequence comparisons

Short tandem repeats are a source of highly polymorphic markers in mammalian genomes. Genetic variation at these hypervariable loci is extensively used for linkage analysis and to identify individuals, and is very useful for interpopulation and interspecies studies. Fifty-nine microsatellite markers from American mink were tested in the ferret, under the same conditions as for the mink. Of the 59, 43 of them (73.5%) amplified a ferret sequence; 5 amplification products differed in size from the respective mink sequences. Ten amplified fragments from ferret were sequenced. The sequences that were identical in size to those from mink displayed a high degree of conservation, with some differences at the repeat motif sites. These results could aid cross-utilization of markers between these two species.     

Population Indices Versus Correlated Density Estimates of Black-Footed Ferret Abundance

ABSTRACT Estimating abundance of carnivore populations is problematic because individuals typically are elusive, nocturnal, and dispersed across the landscape. Rare or endangered carnivore populations are even more difficult to estimate because of small sample sizes. Considering behavioral ecology of the target species can drastically improve survey efficiency and effectiveness. Previously, abundance of the black-footed ferret (Mustela nigripes) was monitored by spotlighting and generating indices of relative abundance because reintroduced populations were slow to establish. Indices, however, lack variance estimates and are costly to generate for the black-footed ferret. We therefore used spotlight surveys and live-trapping in conjunction with a robust mark-recapture estimator to improve abundance monitoring for the black-footed ferret, one of North America's most endangered carnivores. We estimated abundance of the black-footed ferret at Shirley Basin, Wyoming, USA, using correlated density estimates and Program MARK. We compared our results to 2 indices of relative abundance, minimum number alive and predicted number of ferrets from litter counts. The correlated density estimate for the black-footed ferret (N̂_R = 229; 95% CI = 161–298) was similar to minimum number alive (N̂_R = 192) and predicted number of ferrets from litter counts (N̂_R= 235). The efficiency and effectiveness of survey methods we used for the black-footed ferret were high by carnivoran standards. Our results suggest that the sampling approach we utilized can be implemented for a fraction of the cost and effort required to generate 2 indices of relative abundance for the black-footed ferret. Although we recommend managers implement a similar survey approach to monitor abundance of reintroduced populations of the black-footed ferret, analysis with sparse data sets will be problematic. Until the black-footed ferret becomes widespread and abundant at a reintroduction site, spotlighting will remain preferable as a means to generate indices of distribution and relative abundance for the black-footed ferret.     

A comparative analysis of carbon dioxide displacement rates for euthanasia of the ferret

Though carbon dioxide asphyxiation is a common method of euthanasia for laboratory animals, species-specific guidelines have not been established for this procedure in the domestic ferret (Mustela putorius furo). The authors investigated the efficacy and stress effects of carbon dioxide euthanasia in 24 ferrets that had participated in previous experimental protocols. They euthanized ferrets by placing them in cages that were either prefilled with carbon dioxide or gradually filled at a displacement rate of 10%, 20% or 50% of the cage volume per min. Blinded observers subjectively evaluated ferret distress. Prefilling the cage or filling it at a rate of 50% volume per min resulted in less time to recumbency and to last breath than did filling the cage at a slower displacement rate. Slower carbon dioxide displacement rates also caused an increase in ferret blood glucose concentrations, which may indicate distress. Overall, observers found that prefilling the euthanasia cage caused the least stress to ferrets.