Pleiotropic effect of the Black crystal mutation on reproductive indicators in the American mink (Mustela vison)]

The parameters of reproduction were studied in American minks that were homo- and heterozygous for the Black crystal mutation (Cr). The given mutation that changes the hair pigmentation was obtained de novo duration selection of American minks for tame behavior. Apart from changed color, the following reproduction disorders were detected in the Black crystal mutants, as compared to standard animals: (1) delayed entry into the reproductive season in females; (2) greater percentage in both homo- and heterozygous animals of females bearing no offspring; (3) greater early postnatal lethality indices. The most marked suppressing effect on the development of offspring was detected in homozygous females (Cr/Cr), whose progeny perished within a few days after birth. An analysis of reproduction in mutants and standard animals is presented. An attempt was made to explain the conceivable mechanisms that form the basis of disorders detected.     

Functional state of the thyroid gland in the postnatal period in mink of different genotypes]

The thyroid gland functional state was studied by means of 131J-triiodothyronine in minks of two genotypes. The thyroid activity in the standard (dark brown) minks increased from the 3--4th month of postnatal ontogenesis (July--August) and decreased gradually by the 6th month (november). Similar changes in the thyroid activity were found in the Hedlung (white) minks as well. Their thyroid activity was, however, markedly higher on the 3rd month than in the standard minks.     

Effects of 6-MBOA on reproductive function in ponies, mice, rats and mink

The effect on reproduction of the plant derivative 6-methoxybenzoxazolinone (6-MBOA), which stimulates reproductive function in voles, was tested in pony mares, laboratory mice and rats, and mink. There was not a significant effect of intravenous injections of 6-MBOA on the ovarian follicles during the transition between the anovulatory and ovulatory seasons in mares. No significant effect of intraperitoneal injections of 6-MBOA on the weight of uterus or ovaries was found in eight-week-old mice, failing to confirm the results of an earlier report. In immature white rats, 6-MBOA treatment resulted in an increase in uterine weight (P<0.05) at the lowest dose tested (0.03 mug/rat; mean for controls, 34 +/-2 mg; treated, 47 +/-5 mg). However, no significant effect was found on the weights of the ovaries and other glands or in coded scores for ovarian stimulation and uterine fluid distention. Adding 1.5 mg 6-MBOA to the daily feed ration of mink beginning two weeks before the mating season did not affect the mean number of kits born. Nulliparous female mink had smaller (P<0.001) litter size than multiparous females. In addition, of the mink that whelped, there were more (P<0.01) nulliparous females (25 118 ) than multiparous females (9 144 ) that lost one or more kits within 48 hours. These results, however, were not altered by 6-MBOA treatment.     

Effect of iodine on reproductive performance of female mink

Female mink were fed a basal diet supplemented with either 0, 10 100, or 1000 ppm iodine, as potassium iodide, from breeding through lactation. In addition, females were housed in pens sanitized just prior to whelping with 100 or 1000 ppm titratable iodine disinfectant to investigate the effects of these treatments on their reproductive performance. The gestation periods of the iodine-treated mink were shorter than the controls. Kit birth weights were not significantly different from the controls. The average number of kits whelped per female mated in the control group was 5.0. No detrimental effects were observed on litter size or kit survival in the group fed 10 ppm supplemental iodine. Only 2.1 kits per female mated were whelped by the mink fed 100 ppm supplemental iodine and none of the females that received the 1000 ppm supplemental iodine diet whelped. Body weights of kits whelped and nursed by the females that received the 100 ppm supplemental iodine diet were significantly lighter at 4 weeks of age. Kits nursed by females housed in pens sanitized with 100 or 1000 ppm titratable iodine had the greatest biomass at 4 weeks of age.     

Food niche variation of European and American mink during the American mink invasion in north-eastern Belarus

Understanding processes allowing the co-existence of ecologically similar species is important but difficult to study in community ecology. Introductions of alien species are unplanned experiments allowing investigation of co-adaptation of both native and invasive species over a short period. We analysed food niche differentiation between native European mink and alien American mink after invasion of the latter species in Belarus. European mink feed mainly on crayfish, frogs and fish whereas American mink prefer small mammals, fish and frogs. The diet of both species varied between seasons and during the period of alien mink invasion. Concurrent with the progress of American mink invasion, the European mink food niche has narrowed to feeding mainly on frogs, with the proportion of aquatic prey (fish and crayfish) in their diet drastically reduced. In contrast, the American mink food niche became wider during invasion. The breadth was stable but included a varied proportion of different prey categories: namely an increased proportion of aquatic prey and a decreased proportion of water vole and waterfowl. The increase in abundance of American mink saw a decrease in the proportion of larger prey in their diet. When American mink preyed more often on frogs, food niche overlap of both predators increased. This result suggests that arrival of an alien competitor reduced food abundance (exploitative competition) and caused a change in native mink diet.     

Effect of color mutation on the function of the adrenal cortex in chronic feed stress in American mink

Effect of color mutations, headlund and aleutian, on the adrenocortical function was studied in American mink under stress conditions. The adrenocortical function was analysed in the course of gland's incubation in vitro. Natural environmental factors (sharp fall of temperature) and artificially limited feed served as stress factors. It was shown that minks heterozygous for color mutant alleles studied were more resistant to the stressors. This is associated with genetically mediated peculiarities of the action of hypophysial adrenocortical system which is characterized by more adequate reactivity towards stimuli acting. Thus, the effect of heterosis in minks heterozygous for color alleles may well be caused by their increased resistance to stress.     

Position of the embryos of American mink in the fetal chamber at different stages of development]

The spacial position of American mink embryos is characterized by regular changes and is associated with the development and formation of provisory embryonic organs and the uterus. After the implantation the longitudinal axis of the embryo's body lies perpendicularly towards the long axis of the uterus horn. From the end of the 22nd day till birth the embryo moves along the antimesometral side of the fetal chamber by rotation counter clockwise relative to the point of attachment of the alantois stalk. On the 20th day prior to delivery the embryo's body bent as a coil takes a vertical position its fore-part is disposed in the yolk sac cavity, and the hinder part is in the exocoelom. During 17 days before birth the embryo "rolls out" from the yolk sac cavity and occupies the low position in the longitudinal posture of the body. During the following 6 days the prefetus moves towards the opposite side wall of the fetal chamber, takes the upper position and keeps a longitudinal position till the end of the embryonic life.     

Variation in hormonal feedback and reproductive performance in adult rams of different genotypes

Adult Moroccan rams of two different genotypes were compared on the basis of seasonality, fertility and sensitivity to gonadal feedback on the pituitary and hypothalamus. One breed with less seasonal breeding and high fertility, D'Man and one with less fertility and marked seasonal variation in breeding behaviour, Bnihsen. Four animals in each genotype were hemicastrated and 9 mo later castrated, to examine the effect of hormonal control on the hypothalamo-hypophyseal feedback system. Nine months after hemicastration the D'Man breed showed higher gonadotrophine values (LH, FSH). The remaining testicule in turn produced more estradiol-17beta but less testosterone in these rams. The testosterone production was increased in the Bnihsen rams following castration. After castration the FSH values increased rapidly in all animals with higher values for the D'Man rams. LH-release was faster in the hemicastrated rams than in controls. This is the first report on differences for hormonal feedback-systems in adult rams from different genotypes. The hormonal feedback-system is less sensitive for adult rams from breeds with higher fertility and nonseasonaly. In addition to that it was found that a difference seems to exist in the regulation for the release of FSH and LH.     

Regional assignments of eight genes on chromosome 2 in the American mink

Chromosomal rearrangements involving mink chromosome 2 in mink-Chinese hamster and mink-mouse hepatoma somatic hybrids were identified. By means of these rearrangements, we assigned the genes for HK1, GOT1, and PP to 2pter----p22, those for PGD, PGM1 and ENO1 to 2q24.4----qter, and that for NP and ADK to 2pter----p11.1.     

Inbreeding affects fecundity of American mink (Neovison vison) in Danish farm mink

Inbreeding is an increasing problem in farmed mink, because of limited exchange of individuals between farms. In this study, genetic relatedness within seven American mink (Neovison vison) colour strains originating from 13 different mink farms in Denmark was analysed using 21 polymorphic microsatellite loci. We detected large differences in the level of relatedness (range 0.017-0.520) within colour strains. Moreover, a very strong and highly significant negative correlation between the level of relatedness and fecundity was observed (r = 0.536, P < 0.001) [Correction added after online publication on 9 March 2011: r(2) has been changed to r]. To our knowledge, this is the first time that such a correlation has been demonstrated for commercially farmed mink.     

Population studies on feral American mink Mustela vison in Ireland

Populations of feral American mink Mustela vison were investigated in several study areas in Ireland, principally by capture-recapture techniques. The populations were found to be essentially self-regulating, with stress, weight loss and mortality evident during the winter and spring. The highest mean density recorded, in terms of animals per unit length of river or lake shore, was 1.4 individuals km⁻¹ with a peak density of 2.3 individuals km⁻¹, but population densities were considerably lower in most areas. Trappability and population structure, in age, sex and residency classes, varied between habitats, but population turnover was high, leading to complete replacement of individuals in two populations monitored for two years. The availability of the preferred prey, crayfish Austropotamobius pallipes appeared to be a major factor determining population size and preferred breeding areas. Control methods are either unnecessary or are likely to fail in most situations, and may be counterproductive.     

The effect of microsomal enzyme inducing drugs on reproductive function in the ewe.

A number of drugs cause marked increases in the steroid hydroxylase activity of hepatic microsomes. Beginning 2 days after estrus, 117 mature ewes were each given 14 injections over a 27-day period of phenobarbital sodium, diphenylhydantoin, chlorcyclizine HCl or phenylbutazone. Blood samples for luteinizing hormone (LH) and progesterone determination by radioimmunoassay (RIA) were taken on day 10 of the first estrous cycle (day 18 if no heat was observed) and on days 5 and 10 of the second cycle. On day 10 of the second cycle, the ewes were given an intravenous injection of 1 ml of 6% solution of pentobarbitol sodium anesthetic per 4.5 kg body weight, and the length of anesthetic sleep time was measured. The ewes were then killed and corpora lutea and liver were weighed.In 33 ewes treated with either phenobarbitol sodium or phenylbutazone, sleep time was shortened (18 min $\text{vs}$ 29 min in untreated controls, P<.01), indicating that enzyme induction had occurred. For 41 ewes treated with either chlorcyclizine HCl or diphenylhydantoin, sleep time was lengthened to 93 min (P<.01 $\text{vs}$ controls), indicating impaired liver function. Electron micrographs of liver cells verified that enzyme induction or hepatic degeneration had occurred.     

Underwater predatory behaviour of the American mink (Mustela vison)

Fishing behaviour of the American mink ( Mustela vison Schreber) was investigated in the laboratory. Data were recorded using ciné film and tape recorded commentaries. Three species of prey were presented to mink, namely, carp ( Cyprinus curpio ), goldfish ( Carassius auratus ) and minnows ( Phoxinus phoxinus ).
It was found to be necessary to train ranch-bred mink to enter water and catch fish; young mink appeared to be easier to train than adults. Mink spent 5–20 sec under water when fishing; prey had usually previously been located from an aerial vantage point. Predatory behaviour was highly organized sequentially whereas fish were more prone to indulge in unpredictable stratagems; the behaviour of mink and fish were highly correlated.
The mink's efficiency in catching fish was related to prey size (smaller individuals being more vulnerable to capture) and shoaling. Minnows, which form highly organized shoals, were less easily caught when present in large numbers; this was not true of a loosely shoaling species, the carp.
Of the three species of prey presented, vulnerability to capture took the form goldfish> carp> minnow; these differences, however, may have been influenced by the fish's previous experience of underwater predators.     

The effect of environmental temperature on the excretion time of sebum in different genotypes of cattle

The sebum excretion times (SET) were studied in two breeds of cattle, Bos taurus (SH) and the more heat tolerant B. indicus (GB). Both breeds were maintained in thermoneutral (24 degrees C) and hot (32 degrees C) environments. SET was defined as the time between synthesis and release of sebum on to the skin surface. The SET was 7 days in SH and 6 days in GB animals at 24 degrees C but was a day earlier at 32 degrees C for each breed. The changing SET with environmental temperature was associated with an increased rate of synthesis of sebum with increased body temperature.     

The impact of American mink Mustela vison and European mink Mustela lutreola on water voles Arvicola terrestris in Belarus

In the U.K. the impact of introduced American mink Mustela vison , on water voles Arvicola terrestris , may be exacerbated by habitat loss and fragmentation. Pristine wetlands in Belarus, which American mink invaded in the early 1990s, provide a three-pronged opportunity to test this hypothesis. First, we examine the evidence that, even in the unmanaged wetlands of our Belarussian study site, American mink have reduced water vole populations. Second, we ask whether habitat size, type and isolation mitigate the impact of American mink predation. Thirdly, we explore whether water voles are at greater risk of predation from American than European mink because of their patterns of habitat use. Following the invasion of American mink, water voles were most abundant in small, still-water sites, far from river banks, while American mink were most active in large, running-water sites. Small mammal remains were found in a higher percentage of American than European mink scats, and of these, more were water vole in American mink scats. The occurrence of water voles in scats of both mink species declined after the American mink invaded and established. Our results provide at least circumstantial evidence that American mink limit water vole populations even in unmanaged wetland eco-systems, and that they have a greater impact than their European congener at least partly because they make greater use of isolated marshes. Although by no means providing complete protection, the configuration and dispersion of available habitat mitigated the impact of American mink on water voles. This raises the possibility that habitat restoration, especially through the establishment of isolated enclaves, could help reduce the effect of American mink in the U.K. These observations are of broader interest in the context of assessing the effect of multiple pressures on vulnerable species.     

Cytogenetic effect of mitomycin C and cytosine arabinoside on mice of different genotypes]

Cytogenetic effect of mitomycin C (MC) and cytosine arabinoside (CA) on bone marrow cells of male mice of the strains 101/HY, C57BL/6Y C,3H/SnY and of the (C3HX101) F1 hybrids was studied. The frequencies of cells with chromosome aberrations after the treatment with MC at a 5 mg/kg dose were 54,4%; 41,8%; 40,4% and 26,8% in 101H, B6, C3H/Sn mice and in the F1 hybrids (C3HX101) respectively. The frequencies of cells with chromosome aberrations after the treatment with CA at a 500 mg/kg dose were 25,2%; 17,8%; 10,8% and the 101/H, B6, C3H/Sn mice and in the F1 hybrids (C3HX101) respectively. Both mutagens induced the greatest number of chromosome aberrations in the 101/H strain and the smallest number in the F1 hybrid (C3HX101). A positive correlation was established between the levels of induced and spontaneous chromosome lesions.