Effects of diet on captive black-footed ferret (Mustela nigripes) food preference

Black-footed ferrets (Mustela nigripes) are both habitat and prey specialists that depend on prairie dogs (Cynomys spp.) for food and utilize prairie dog burrows for refuge. In this study we investigated the effects of captive diet during early development on adult black-footed ferret food preferences. To test the hypothesis that early diet affects the food preferences of adult black-footed ferrets, we exposed 22 kits (divided into three experimental groups) to different quantities of prairie dog in the diet: no prairie dog, prairie dog three times per week, and prairie dog daily during the assumed sensitive period for olfactory imprinting, i.e., between 60–90 postnatal days. At age 5 months, kits were individually tested in a food choice cafeteria trial. Results indicated that higher amounts of prairie dog in the ferrets' early diet led to a higher preference for this food item when ferrets reached adulthood. These results have important implications for black-footed ferret recovery and have been considered in the reintroduction protocol. © 1996 Wiley-Liss, Inc.     

Courtship patterns in induced oestrous and natural oestrous domestic ferrets (Mustela putorius furo)

Ten anoestrous female domestic ferrets (Mustela putorius furo) had estrus artificially induced by injection of porcine follicle stimulating hormone. Pre-copulatory activities were defined, quantitatively analyzed, and compared to the pre-copulatory activities of 10 control females placed with the same male ferrets. Lag sequential analysis was used to prepare the behavioral matrices. Matrices were compared with an equality of proportions test. Courtship patterns between the 2 groups did not differ significantly.     

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.     

Black-footed ferret (Mustela nigripes) behavioral development: aboveground activity and juvenile play

We studied the behavioral development of black-footed ferrets (Mustela nigripes) from 6 to 16 post-natal weeks. At 6 weeks of age, kits are still lactating and depend on their mother for survival, while at 16 weeks, ferret young start achieving independence from their mother and littermates. Behavioral observations were obtained by placing videomonitors in the litters’ cages, nest boxes and in outdoor naturalistic enclosures. Captive-raised black-footed ferrets displayed nocturnal activity patterns, although they tended to appear aboveground at certain daytime hours presumably influenced by the established feeding and cleaning regimes. Growing ferrets began emerging aboveground at approximately 7 post-natal weeks and diel activity steadily increased as kits matured. The most manifest behavioral changes (appearance of new motor patterns, increase in aboveground play and in neck-biting behaviors) occurred from post-natal week 8 to week 12. This coincides with the period of maximum growth for ferrets and with a sensitive phase for the development of food preferences in this species. Changes from the 12 to the 16 post-natal weeks involved an increase in aboveground activity, including a higher frequency of scent-marking behaviors. Information provided in this study has important implications for enhancing the captive management of this endangered carnivore.     

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.     

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.     

Genetic diversity and fitness in black-footed ferrets before and during a bottleneck

The black-footed ferret (Mustela nigripes) is an endangered North American carnivore that underwent a well-documented population bottleneck in the mid-1980s. To better understand the effects of a bottleneck on a free-ranging carnivore population, we used 24 microsatellite loci to compare genetic diversity before versus during the bottleneck, and compare the last wild population to two historical populations. We also compared genetic diversity in black-footed ferrets to that of two sibling species, the steppe polecat (Mustela eversmanni) and the European polecat (Mustela putorius). Black-footed ferrets during the bottleneck had less genetic diversity than steppe polecats. The three black-footed ferret populations were well differentiated (F(ST) = 0.57 +/- 0.15; mean +/- SE). We attributed the decrease in genetic diversity in black-footed ferrets to localized extinction of these genetically distinct subpopulations and to the bottleneck in the surviving subpopulation. Although genetic diversity decreased, female fecundity and juvenile survival were not affected by the population bottleneck.     

Age-dependent changes in sperm production, semen quality, and testicular volume in the black-footed ferret (Mustela nigripes)

The black-footed ferret (Mustela nigripes), which was extirpated from its native North American prairie habitat during the 1980s, is being reintroduced to the wild because of a successful captive-breeding program. To enhance propagation, the reproductive biology of this endangered species is being studied intensively. The typical life span of the black-footed ferret is approximately 7 yr. Female fecundity declines after 3 yr of age, but the influence of age on male reproduction is unknown. In this study, testis volume, seminal traits, sperm morphology, and serum testosterone were compared in 116 males from 1 to 7 yr of age living in captivity. Results demonstrated that testes volume during the peak breeding season was similar (P > 0.05) among males 1 to 5 yr of age, reduced (P < 0.05) among males 6 yr of age, and further reduced (P < 0.05) among males 7 yr of age. Motile sperm/ejaculate was similar in males 1 to 6 yr of age but diminished (P < 0.05) in those 7 yr of age. Males at 6 and 7 yr of age produced fewer (P < 0.05) structurally normal sperm than younger counterparts; however, serum testosterone concentrations were not reduced (P > 0.05) in older males. Histological comparison of testicular/epididymal tissue from 5- and 7-yr-old black-footed ferrets confirmed that the interval between these two ages may represent a transitional period to reproductive senescence. In summary, functional reproductive capacity of male black-footed ferrets exceeds that of females by at least 2 yr. Testes and seminal quality are indistinguishable among males 1 to 5 yr of age, with progressive reproductive aging occurring thereafter.     

Cloned ferrets produced by somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) offers great potential for developing better animal models of human disease. The domestic ferret (Mustela putorius furo) is an ideal animal model for influenza infections and potentially other human respiratory diseases such as cystic fibrosis, where mouse models have failed to reproduce the human disease phenotype. Here, we report the successful production of live cloned, reproductively competent, ferrets using species-specific SCNT methodologies. Critical to developing a successful SCNT protocol for the ferret was the finding that hormonal treatment, normally used for superovulation, adversely affected the developmental potential of recipient oocytes. The onset of Oct4 expression was delayed and incomplete in parthenogenetically activated oocytes collected from hormone-treated females relative to oocytes collected from females naturally mated with vasectomized males. Stimulation induced by mating and in vitro oocyte maturation produced the optimal oocyte recipient for SCNT. Although nuclear injection and cell fusion produced mid-term fetuses at equivalent rates (approximately 3-4%), only cell fusion gave rise to healthy surviving clones. Single cell fusion rates and the efficiency of SCNT were also enhanced by placing two somatic cells into the perivitelline space. These species-specific modifications facilitated the birth of live, healthy, and fertile cloned ferrets. The development of microsatellite genotyping for domestic ferrets confirmed that ferret clones were genetically derived from their respective somatic cells and unrelated to their surrogate mother. With this technology, it is now feasible to begin generating genetically defined ferrets for studying transmissible and inherited human lung diseases. Cloning of the domestic ferret may also aid in recovery and conservation of the endangered black-footed ferret and European mink.     

Evaluation of a black-footed ferret resource utilization function model

Resource utilization function (RUF) models permit evaluation of potential habitat for endangered species; ideally such models should be evaluated before use in management decision-making. We evaluated the predictive capabilities of a previously developed black-footed ferret (Mustela nigripes) RUF. Using the population-level RUF, generated from ferret observations at an adjacent yet distinct colony, we predicted the distribution of ferrets within a black-tailed prairie dog (Cynomys ludovicianus) colony in the Conata Basin, South Dakota, USA. We evaluated model performance, using data collected during post-breeding spotlight surveys (2007–2008) by assessing model agreement via weighted compositional analysis and count-metrics. Compositional analysis of home range use and colony-level availability, and core area use and home range availability, demonstrated ferret selection of the predicted Very high and High occurrence categories in 2007 and 2008. Simple count-metrics corroborated these findings and suggested selection of the Very high category in 2007 and the Very high and High categories in 2008. Collectively, these results suggested that the RUF was useful in predicting occurrence and intensity of space use of ferrets at our study site, the 2 objectives of the RUF. Application of this validated RUF would increase the resolution of habitat evaluations, permitting prediction of the distribution of ferrets within distinct colonies. Additional model evaluation at other sites, on other black-tailed prairie dog colonies of varying resource configuration and size, would increase understanding of influences upon model performance and the general utility of the RUF. © 2011 The Wildlife Society.     

Canine distemper in black-footed ferrets (Mustela nigripes) from Wyoming

In September and October 1985, six black-footed ferrets (Mustela nigripes) were captured from the only known population, located near Meeteetse, Wyoming for captive propagation. Two days following capture an adult male showed signs of canine distemper and an adult female displayed similar signs 7 days postcapture; these infections were undoubtedly acquired prior to capture. Subsequently the four remaining captive black-footed ferrets also developed canine distemper and all eventually died. Clinical signs included severe pruritus, hyperkeratosis and progressive loss of body condition. A few animals had intermittent diarrhea and respiratory disease. Intranuclear and intracytoplasmic inclusion bodies were numerous in epithelial tissues and two black-footed ferrets had a mild to moderate meningoencephalitis. Canine distemper virus was isolated from four animals and paramyxovirus nucleocapsids were observed by electron microscopy of feces from all affected black-footed ferrets. Antibodies to canine distemper virus were not detected in sera of sick black-footed ferrets. Antibodies to canine distemper virus were found in sera of badgers (Taxidea taxus) and coyotes (Canis latrans) collected in the Meeteetse area in 1986. Most free-ranging black-footed ferrets in the colony apparently died of canine distemper during the summer and fall of 1985. An attempt was made to capture all surviving animals in the affected area in order to abort the epizootic and provide black-footed ferrets for captive propagation.     

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.     

Transcervical artificial insemination in the domestic ferret (Mustela putorius furo)

The research was undertaken to develop a successful nonsurgical procedure for artificially inseminating ferrets. A fiberoptic endoscope used in conjunction with a specially designed speculum and catheter permitted cervical catheterization and intrauterine insemination. Sperm were collected from the cauda epididymides of 10 discarded breeder males; the number of sperm in diluted samples used for insemination ranged from 4.4–13.6 × 10⁶/100 μl with progressive motility of sperm ranging from 40 to 60%. Sperm collected from each male were diluted with an egg-yolk extender (TEST) and used to inseminate 8–12 females, with deposition of sperm intravaginally or transcervically into the uterine body 0 or 24 hr after an ovulatory injection of human chorionic gonadotropin (hCG). The vaginal inseminations were used as a control, and no pregnancies resulted after insemination of 26 females. Intrauterine inseminations resulted in 4/24 (17%) of the ferrets pregnant when hCG administration was coincident with insemination, and 19/24 (79%) of the ferrets were pregnant when inseminations were done 24 hr after hCG administration. All inseminated females were euthanized on day 20 after insemination to count fetuses. The mean number of fetuses was 3.1 (range, 1–8). The number (millions) of motile sperm inseminated (X) had a significant effect on the percentage of fetuses (Y). Regression analysis indicated a linear relationship between the two variables, with an R² value of 0.99 and a line of best fit described by the equation Y = 0.029 + 0.034 X. This paper is the first report of transcervical artificial insemination in the domestic ferret (Mustela putorius furo). The method can serve as a model for application to ferrets and other mammals, particularly endangered species. Zoo Biol 17:393–404, 1998. © 1998 Wiley-Liss, Inc.     

Nonsurgical collection and nonsurgical transfer of preimplantation embryos in the domestic rabbit (Oryctolagus cuniculus) and domestic ferret (Mustela putorius furo)

The objective of this study was to develop nonsurgical methods of embryo collection and transfer in domestic rabbits (Oryctolagus cuniculus) and domestic ferrets (Mustela putorius furo) to serve as models for use in mammals in which surgical procedures are the usual means for applying embryo transfer technology. Specially designed transcervical catheters were used together with a fibre optic endoscope to visualize and then catheterize the rabbit and ferret cervices. Five consecutive transcervical uterine flushes in each of eight superovulated female rabbits 78-89 h after an ovulatory injection of LH resulted in the retrieval of 187 embryos, for an average of 23 embryos per rabbit. A total of 116 embryos were nonsurgically transferred to the uteri of ten recipients, and resulted in 23 young (20%). Eight rabbits (80%) produced young with an average litter size of 2.88 (range 1-7). Ten consecutive transcervical uterine flushes in each of 37 female ferrets 145-178 h after an ovulatory injection of hCG resulted in the retrieval of 324 embryos, an average of 8.76 embryos per ferret. A total of 251 embryos from 27 donors were nonsurgically transferred to the uteri of 31 recipients, and resulted in 65 young (26%). Twenty-eight of the recipients (90%) were initially pregnant, as indicated by postpartum necropsies, and twenty-two ferrets (71%) produced young. The average litter size was 2.95 (range 1-7). This is the first report of live births resulting from the nonsurgical collection of embryos from a donor followed by nonsurgical transfer of those same embryos to a synchronous recipient. The methods reported here can serve as models for use in other mammals in which direct visualization and manipulation of the cervix are not possible, and will be particularly useful in endangered species.     

Vaccination with F1-V fusion protein protects black-footed ferrets (Mustela nigripes) against plague upon oral challenge with Yersinia pestis

Previous studies have established that vaccination of black-footed ferrets (Mustela nigripes) with F1-V fusion protein by subcutaneous (SC) injection protects the animals against plague upon injection of the bacterium Yersinia pestis. This study demonstrates that the F1-V antigen can also protect ferrets against plague contracted via ingestion of a Y. pestis-infected mouse, a probable route for natural infection. Eight black-footed ferret kits were vaccinated with F1-V protein by SC injection at approximately 60 days-of-age. A booster vaccination was administered 3 mo later via SC injection. Four additional ferret kits received placebos. The animals were challenged 6 wk after the boost by feeding each one a Y. pestis-infected mouse. All eight vaccinates survived challenge, while the four controls succumbed to plague within 3 days after exposure. To determine the duration of antibody postvaccination, 18 additional black-footed ferret kits were vaccinated and boosted with F1-V by SC injection at 60 and 120 days-of-age. High titers to both F1 and V (mean reciprocal titers of 18,552 and 99,862, respectively) were found in all vaccinates up to 2 yr postvaccination, whereas seven control animals remained antibody negative throughout the same time period.     

Dirofilaria immitis: experimental infections in the ferret (Mustela putorius furo)

The ferret, Mustela putorius furo, was found to be susceptible to Dirofilaria immitis infection when exposed to low (14) or high (280-420) numbers of infective larvae harvested from Aedes aegypti. Eight ferrets (half of them cortisonized) were inoculated subcutaneously with 14 larvae each. All of them were subsequently found to harbor D. immitis in the heart, and all but one of them had worms of both sexes. Six of these ferrets were examined for microfilaremia at 31 to 35 weeks after inoculation; 3 were positive (one observed only at postmortem examination) and there was evidence that fertilization of female worms had occurred in one other. Females up to 25.5 cm and males up to 16.0 cm were recovered. There was no evidence that the cortisonization of some ferrets had affected the infections. Both male and female ferrets became infected. Four cortisonized ferrets were inoculated with 280 or 420 larvae of D. immitis (divided equally between subcutaneous and intraperitoneal routes). All of them died 16 to 18 weeks after inoculation, yielding 102 to 125 immature D. immitis. In these lethal infections, worms were recovered from the heart and adjoining vessels, and also from vascular and extravascular sites throughout the body.     

Cystic renal disease in the domestic ferret

Cystic renal diseases in domestic ferrets are a common anecdotal finding but have received scant systematic assessment. We performed a 17-y, case-control retrospective analysis of the medical records of 97 ferrets housed at our institution between 1987 and 2004, to determine the prevalence and morphotypes of cystic renal diseases in this species. Histologic sections stained with hematoxylin and eosin, Masson trichrome, or periodic acid-Schiff were evaluated by a comparative pathologist, and statistical analysis of hematologic and serum chemistry values was correlated with morphologic diagnosis. Of the 97 available records, 43 were eliminated due to lack of accompanying tissues. Of the 54 remaining cases, 37 (69% prevalence) had documented renal cysts, and 14 of the 54 ferrets (26%) had primary polycystic disease consisting of either polycystic kidney disease affecting renal tubules or, more commonly, glomerulocystic kidney disease. Secondary polycystic lesions were identified in 11 ferrets (20%), and 12 ferrets (22%) exhibited focal or isolated tubular cysts only as an incidental necropsy finding. Ferrets with secondary renal cysts associated with other developmental anomalies, mesangial glomerulopathy, or end-stage kidney disease had hyperphosphatemia and elevated BUN in comparison with those with primary cystic disease and elevated BUN compared with those without renal lesions. Although reflecting institutional bias, these results implicate primary and secondary cystic renal diseases as highly prevalent and underreported in the domestic ferret. In addition to the clinical implications for ferrets as research subjects and pets, these findings suggest a potential value for ferrets as a model of human cystic renal diseases.     

Putative chemosignals of the ferret (Mustela furo) associated with individual and gender recognition

Quantitative stir bar sorptive extraction methods, both in the aqueous and headspace modes, followed by thermal desorption gas chromatography-mass spectrometry were used to investigate individual variations in the volatile components of male and female ferret (Mustela furo) urine. The urinary profiles were further compared with volatile profiles of anal gland secretions of breeding male and female ferrets. Thirty volatile compounds were quantified in male and female urine. Among them, 2-methylquinoline was unique to male urine. Four ketones (4-heptanone, 2-heptanone, o-aminoacetophenone, and a dimethoxyacetophenone) and several nitrogen compounds (e.g., 2,5-dimethylpyrazine, quinoline, 4-methylquinazoline) and low levels of three unidentified nonsulfur compounds were significantly more abundant in males than in females. Quantitative comparison of 30 volatile urinary compounds showed several statistically significant differences between the sexes and individuals of the same sex. These findings suggest that ferrets may use urine marking for sex and individual recognitions. Ten of the 26 compounds identified in anal gland secretions from females and males were also found in urine. However, most of the major compounds (thietanes, dithiolanes, and indole) in anal glands were not present in urine. This suggests that urine may convey specific signals that differ from those of anal glands. Additionally, 10 volatiles (two aldehydes, five ketones, benzothiazole, 2-methylquinoline, and 4-methylquinazoline), not previously identified, were found in ferret anal gland secretions. Among the new compounds, o-aminoacetophenone was found only in males, while only traces of this compound were found in females. Similar results were previously obtained in anal glands of three other Mustela species. These findings provide new information about the constituents of urine and volatile components of anal gland secretions in ferrets.     

Reproductive biology and management of captive black-footed ferrets (Mustela nigripes)

A captive breeding program is being conducted with black-footed ferrets (Mustela nigripes), an endangered species. Results of 5 years of study are reported. Simple, but specialized, nontraumatic handling techniques allowed assessment of reproductive status with minimal stress, which was important in breeding management. Black-footed ferrets are sexually mature and may successfully reproduce in their 1st year. Proestrus lasts approximately 2-3 weeks. Duration of estrus in unbred females was 32–42 days; females usually bred within 20 days. Most breeding activity occurred during April. Mean gestation length was 42.7 days (±0.7, range 42–45 days), litter size averaged 3.0 kits (±1.4, range 1–6 kits), and weaned kits/litter averaged 2.4 (±1.7, range 1–6 kits). Weaning rate of kits was 80%. Sex ratio of kits was essentially 1:1. Productivity was greatest among females ?3 years of age. Rapid expansion of the captive population is possible and will be important for genetic management of the species and for achieving the primary goal of the recovery program, which is to return black-footed ferrets to the wild.     

Activity in the ferret: oestradiol effects and circadian rhythms

The present study was conducted to determine whether oestradiol increases activity in the European ferret (Mustela furo), whether this effect is sexually dimorphic, and whether a 24-h rhythm is present in the ferret's daily activity. The activity of male and female adult, postpubertally gonadectomized ferrets was monitored while they were maintained singly on a 13:11 light-dark cycle, before and after implantation with oestradiol-17β. Gonadectomized male and female ferrets exhibited equal levels of activity, and neither sex exhibited a significant change in activity following oestradiol implantation. None of the ferrets exhibited a strong circadian rhythm, although weak 24-h rhythms and shorter harmonic rhythms were present. Golden hamsters (Mesocricetus auratus), monitored in an identical manner, exhibited strong circadian rhythms. It was concluded that oestradiol administration may not cause an increase in activity in the ferret, and that this species lacks a strong circadian activity rhythm.