Fur-farming is a politically sensitive issue today. Therefore, discussions on the welfare situation of commercially farmed fur animals may be particularly valuable. The aim of this Short Communication is to address some issues, in addition to those covered in the review of Nimon and Broom on the welfare of farmed mink (Animal Welfare 1999, 8: 205-228), that may have received too little attention. This Short Communication addresses domestication and animal welfare, indispensable resources and behaviours of farmed mink, and the use of negative and positive indicators of welfare in research on farmed mink.

Farmed mink are known for showing stereotypies and tail biting, behaviours that are mostly viewed as indicators of reduced welfare. Among the factors that are often described as being relevant for the welfare of mink are food management systems, age at weaning, and type/presence of nest boxes and bedding. In the present study of commercially farmed mink, all of these factors have been integrated in one housing system. The occurrence of stereotypies and tail biting were observed at six Dutch mink farms, which differed from one another with respect to the number of modifications and the time since the introduction of these modifications. On each farm, 60 non-lactating female mink were observed during winter and 50 lactating female mink (with kits) were observed during summer. Mink on the farm with the most modifications spent 4.1% and 0.8% of their time performing stereotypies in winter and in summer, respectively. Mink on the farm with the least modifications spent 32% and 10.9% of their time performing stereotypies in winter and in summer, respectively. The occurrence of stereotypic behaviour in winter gradually increased as feeding time approached. This gradual increase was not observed at the farm with the least modifications. In general, mink spent less time performing stereotypies in summer than in winter. No clear differences were found between the farms for the occurrence of tail biting in relation to the modifications of the new system, although one farm showed a lower percentage (4%) of tail biters during summer. In conclusion, the farms that had introduced more modifications into their husbandry system housed animals showing less stereotypic behaviour. The results of this field study demonstrate an inverse relationship between the number of modifications and the occurrence of stereotypies; because of the experimental design, however, a causal relationship is not implied. Further work is required to investigate the impact of each measure both in isolation and in the integrated system under more carefully standardised conditions.

Early research on farmed mink was predominantly concerned with increased productivity; however, in recent years there have been an increasing number of studies related to welfare. The biology of feral mink has also become better understood, and such knowledge can aid in the assessment of welfare on farms, or in the interpretation of problems related to captivity. This paper is a comprehensive review of research pertinent to the welfare of farmed American mink, Mustela vison, in relation to their housing and management. It indicates how housing conditions might be changed to improve welfare, and where our present knowledge is insufficient. Many significant aspects of mink behaviour in the wild, such as their lack of social contact, their tendency to travel long distances and use several den sites, and regular swimming and diving, are denied them in captivity. Farmed mink also show high levels of stereotypy, suggesting that their welfare is not good. Welfare may be improved by appropriate environmental enrichment and changes in the social environment of farmed mink. In general, studies aimed at improving housing conditions have been limited in scope and outlook.

Most on-farm welfare assessment systems have been developed for use in dairy and pig farms. These production systems are non-synchronous, in the sense that the same processes occur continuously throughout the year. Animal welfare during most or all phases of production may therefore be assessed at any time of the year, except for some effects of season. Many domesticated farm animals such as sheep, goats, deer and mink are seasonally synchronised in their production, in the same way as were their wild ancestors. A comprehensive welfare assessment system including animal-based indicators for these species must therefore take an entire production cycle into consideration. This can be illustrated by a welfare assessment protocol developed and tested by the Danish Institute of Agricultural Sciences (DIAS) for mink production. The DIAS concept is based on indicators from four sources: the system, the system's management, animal behaviour, and animal health. An advantage of seasonality is that the measurement of welfare indicators can be optimised and standardised in terms of age/season and sample size, making reliable results relatively cheap to obtain. Furthermore, there is ample time to plan the requisite interventions. A disadvantage of seasonality is that the entire herd may have been at risk when a welfare problem is disclosed by direct animal-based indicators; for example, the entire herd may have been exposed to a social grouping causing bite marks, which can be observed at pelting. Based on observation of the social grouping, this can be corrected before fighting and biting occurs. Based on observation of the bite marks, corrections are postponed until next season. Welfare assessment intended for decision support in a synchronous production system should therefore include a higher proportion of early indicators based on the system and management, in order to prevent the development of potential welfare problems involving the entire herd. The assessment of animal-based indicators may be relatively cheap and more reliable in synchronous production compared to non-synchronous production, and these indicators are therefore given high priority as they reflect the welfare resulting from the corrections made based on indirect system and management indicators.

The opportunity to perform play behaviour may be an important ontogenic activity that stimulates behavioural variability and may enhance an individual's coping capacity later in life. Play behaviour in juveniles may be enhanced by the presence of cage enrichments relevant to the animal's motivations and natural behavioural repertoire. The present study aimed to investigate play behaviour in juvenile farmed mink reared and housed with the cage enrichments standard for the Dutch housing system (ie a cylinder and platform) and in an experimental group of animals with the same standard enrichments but with additional access to swimming water. Juvenile mink with access to swimming water played significantly more in the main cage than mink reared and housed with the cylinder and platform but without swimming water. The results suggest that swimming water presents the animals with biologically relevant stimuli that directly or indirectly influence the development of play behaviour. Specific implications for the animals' long-term welfare are discussed. Future studies should elucidate the effects of juvenile play on the occurrence of abnormal behavioural patterns in adulthood more precisely and more thoroughly.

Animal welfare is a major issue in Europe, and the production of mink, Mustela vison, has also been under debate. One common method of solving animal welfare problems is to adapt the environment to fit the behavioural needs of the animals. In comparison with other forms of husbandry, the mink production environment has remained relatively unchanged over the years and provides for some of the most obvious needs of mink. Whether today's typical housing conditions adequately meet the welfare requirements of mink is currently a topic of discussion. An alternative approach to improving welfare is to modify the animals so that they are better adapted to farming conditions. In large-scale animal production, handling of the individual can be a sporadic event, making an animal's inherent characteristics for temperament and adaptability important factors to consider with respect to its resultant welfare.

In this review we present and discuss experiments on behavioural selection for temperament, and against undesirable behaviours, such as fur chewing, in mink. Fur chewing behaviour can be reduced by selection, apparently without any negative effects, whereas only a little is known about the nature and consequences of selecting against stereotypic behaviours. Long-term selection experiments have shown that it is possible to reduce fearfulness in farmed mink. Using a relatively simple test, it is possible for farmers to add behavioural measurements to their normal selection criteria and thereby improve the welfare of farmed mink.

Previous studies have shown that male mink (Mustela vison) removed from their mothers at seven weeks of age develop more tail-biting than males left with their mothers until six months. Mink in the wild do not damage their own pelts in this way, and such behaviour may well be an indication of chronic stress.

The aim of this experiment was to investigate further the causes of tail-biting by considering female young as well as male, and by lowering the age at which the late-weaned ‘ mink were separated from their mother to 11 weeks, by which age their period of socialization should be complete. This was to generate results of more practical use to farmers, who cannot leave all young with their mothers until six months of age for reasons of space. Mink removed from their mothers at seven or eleven weeks of age did indeed differ in the incidence of tail-biting. Early-weaned ‘females were more likely than late-weaned females to have bitten their tails at six months of age. A similar result was evident as a trend for both sexes at ten months. Furthermore, at this age, some animals ‘ tail tips were completely bald and such animals were all early-weaned.

Where provided with plastic drinker dishes, early-weaned animals were also more likely to chew these. Thus weaning age had long-lasting effects on a number of oral behaviour patterns. These results suggest that young animals predisposed to tail-bite might be diverted by the provision of other objects to chew, and that if problems of over-crowding are avoided, leaving mink kits with their mothers until 11 weeks might improve their welfare.

The WelFur project aims at the development of on-farm welfare assessment protocols for farmed foxes (the blue fox [Vulpes lagopus], the silver fox [Vulpes vulpes]) and mink (Neovison vison). The WelFur protocols are based on Welfare Quality® (WQ) principles and criteria. Here, we describe the WelFur protocols after two years of developmental work. Reviews for each of the 12 WQ welfare criteria were written for foxes and mink to identify the welfare measures that have been used in scientific studies. The reviews formed the basis for potential measures to be included in the WelFur protocols. All measures were evaluated for their validity, reliability and feasibility. At present, we have identified 15 fox and 9 mink animal-based (or outcome-based) welfare measures, and 11 and 13 input-based (resource-based or management-based) measures. For both foxes and mink, each of the four WQ principles is judged by at least one criterion, and seven out of the 12 criteria include animal-based measures. The protocols will be piloted in 2012. Using the WQ project and protocols as a model has been a fruitful approach in developing the WelFur protocols. The effects of the WelFur protocols will provide benchmarks from which the welfare of animals on European fur farms can be assessed.

In this study we present a semi-random sampling method developed for the sampling of mink (Neovison vison) for on-farm welfare assessments according to the WelFur-Mink system. The only information required for implementation of this method is the number of cages in use in each shed on the farm. The representativeness of samples selected with this method was evaluated in relation to the physical characteristics of the farm and the mink characteristics by simulated sampling on a farm with a complicated structure in the growth period. The selection of 10,000 samples was simulated. The trueness was, in general, high, ie the method has no systematic skewness. The precision was low for certain factors due to the high variation within sheds. The sampling in sections of six adjacent cages means that it is often not possible to select a sample which is an exact representation of the mink and their housing environment. If accepting a deviation of ± one cage section, the estimated probability of selecting a representative sample was high for most of the individual factors. However, the estimated probability of selecting a sample that is representative according to all factors was rather low. This deviation from exact representativeness ought to be evaluated in the light of the increased feasibility and repeatability offered by the method. Also, we expect that the representativeness of samples selected with this method will be higher on other less-complicated farms. We suggest that this simple method balances feasibility and representative sampling in a way that makes it useful in the WelFur-Mink system.

In the mink industry, feed costs are the largest variable expense and breeding for feed efficient animals is warranted. Implementation of selection for feed efficiency must consider the relationships between feed efficiency and the current selection traits BW and litter size. Often, feed intake (FI) is recorded on a cage with a male and a female and there is sexual dimorphism that needs to be accounted for. Study aims were to (1) model group recorded FI accounting for sexual dimorphism, (2) derive genetic residual feed intake (RFI) as a measure of feed efficiency, (3) examine the relationship between feed efficiency and BW in males (BWM) and females (BWF) and litter size at day 21 after whelping (LS21) in Danish brown mink and (4) investigate direct and correlated response to selection on each trait of interest. Feed intake records from 9574 cages, BW records on 16 782 males and 16 875 females and LS21 records on 6446 yearling females were used for analysis. Genetic parameters for FI, BWM, BWF and LS21 were obtained using a multivariate animal model, yielding sex-specific additive genetic variances for FI and BW to account for sexual dimorphism. The analysis was performed in a Bayesian setting using Gibbs sampling, and genetic RFI was obtained from the conditional distribution of FI given BW using genetic regression coefficients. Responses to single trait selection were defined as the posterior distribution of genetic superiority of the top 10% of animals after conditioning on the genetic trends. The heritabilities ranged from 0.13 for RFI in females and LS21 to 0.59 for BWF. Genetic correlations between BW in both sexes and LS21 and FI in both sexes were unfavorable, and single trait selection on BW in either sex showed increased FI in both sexes and reduced litter size. Due to the definition of RFI and high genetic correlation between BWM and BWF, selection on RFI did not significantly alter BW. In addition, selection on RFI in either sex did not affect LS21. Genetic correlation between sexes for FI and BW was high but significantly lower than unity. The high correlations across sex allowed for selection on standardized averages of animals’ breeding values (BVs) for RFI, FI and BW, which yielded selection responses approximately equal to the responses obtained using the sex-specific BVs. The results illustrate the possibility of selecting against RFI in mink with no negative effects on BW and litter size.

Synthetic α-tocopherol has eight isomeric configurations including four 2R (RSS, RRS, RSR, RRR) and four 2S (SRR, SSR, SRS, SSS). Only the RRR stereoisomer is naturally synthesised by plants. A ratio of 1·36:1 in biopotency of RRR-α-tocopheryl acetate to all-rac-α-tocopheryl acetate is generally accepted; however, studies indicate that neither biopotency of α-tocopherol stereoisomers nor bioavailability between them is constant, but depend on dose, time, animal species and organs. A total of forty growing young male mink were, after weaning, assigned one of the following treatments for 90 d: no α-tocopherol in diet (ALFA_0), 40 mg/kg RRR-α-tocopheryl acetate (NAT_40), 40 mg/kg all-rac-α-tocopheryl acetate (SYN_40) and 80 mg/kg feed all-rac-α-tocopheryl acetate (SYN_80). Mink were euthanised in CO2 and blood was collected by heart puncture. Mink were pelted and liver, heart, lungs, brain and abdominal fat were collected for α-tocopherol stereoisomer analysis. The proportion of RRR-α-tocopherol decreased in all organs and plasma with increasing amount of synthetic α-tocopherol stereoisomers in the diet (P≤0·05), whereas the proportion of all synthetic α-tocopherol stereoisomers increased with increasing amount of synthetic α-tocopherol stereoisomers in the diet (P≤0·05). The proportion of α-tocopherol stereoisomers in plasma, brain, heart, lungs and abdominal fat showed the following order: RRR>RRS, RSR, RSS>Σ2S, regardless of α-tocopherol supplement. The liver had the highest proportion of Σ2S stereoisomers, and lowest proportion of RRR-α-tocopherol. In conclusion, distribution of α-tocopherol stereoisomers differs with dose and form of α-tocopherol supplementation. The results did also reveal the liver’s role as the major organ for accumulation of Σ2S α-tocopherol stereoisomers.

Invasive alien species can have widespread negative effects on native biodiversity. We investigated the prospects of engaging hunters in large-scale collaborative efforts to control non-native mink Neovison vison populations in Norway. We invited members of the Norwegian Association of Hunters and Anglers to complete an online questionnaire to ascertain their support for conservation and their level of effort to remove mink, in the context of hunting motivations and bounty payments. The general interest in mink control programmes was low but participants perceived the mink to be of conservation concern. Bounty payments influenced mink catches, with hunters who received payments catching a mean of 4.70 more individuals per hunter than those who did not receive payments (P < 0.001). Mink hunters who preferred to hunt alone and had no preference for hunting locally reportedly caught on average 1.87 more mink per hunter than those who preferred to hunt in company (P < 0.001). The majority of hunters preferred government-led programmes (47%), and investment in bounty programmes (52%) was their main recommendation to improve mink hunting. Hunters can be a valuable component of a mink removal task force and could decrease the likelihood of recolonization of mink in the buffer areas of core conservation target areas.

A sufficient but balanced vitamin supplementation is a prerequisite for a satisfactory growth pattern and an effective immune system in mink and all other species. The fat-soluble vitamins are very sensitive to over- or under-supply because they interact with each other with respect to dose–response and chemical form. The purpose of the present study was to investigate the effect of increasing the amount of retinol in combination with RRR-α-tocopherol or all-rac-α-tocopherol in the feed given to growing mink on their retinol, cholecalciferol and α-tocopherol concentrations in plasma and selected organs. The results showed that the mink met their retinol requirements from the basal diet, but there were no negative effects of supplying various amounts of retinol on their plasma α-tocopherol concentrations. On the other hand, the study showed that the cholecalciferol status in plasma, assessed as the 25-hydroxycholecalciferol concentration, was low when retinol was supplemented in the feed at high levels. In addition, supplementation with RRR-α-tocopherol in the feed negatively affected the plasma concentration of 25-hydroxycholecalciferol compared with supplementation with all-rac-α-tocopherol. In general, female mink had higher concentrations of fat-soluble vitamins in plasma than male mink.

The aim of this study was to determine the genetic background of longitudinal residual feed intake (RFI) and BW gain in farmed mink using random regression methods considering heterogeneous residual variances. The individual BW was measured every 3 weeks from 63 to 210 days of age for 2139 male+female pairs of juvenile mink during the growing-furring period. Cumulative feed intake was calculated six times with 3-week intervals based on daily feed consumption between weighing’s from 105 to 210 days of age. Genetic parameters for RFI and BW gain in males and females were obtained using univariate random regression with Legendre polynomials containing an animal genetic effect and permanent environmental effect of litter along with heterogeneous residual variances. Heritability estimates for RFI increased with age from 0.18 (0.03, posterior standard deviation (PSD)) at 105 days of age to 0.49 (0.03, PSD) and 0.46 (0.03, PSD) at 210 days of age in male and female mink, respectively. The heritability estimates for BW gain increased with age and had moderate to high range for males (0.33 (0.02, PSD) to 0.84 (0.02, PSD)) and females (0.35 (0.03, PSD) to 0.85 (0.02, PSD)). RFI estimates during the growing period (105 to 126 days of age) showed high positive genetic correlations with the pelting RFI (210 days of age) in male (0.86 to 0.97) and female (0.92 to 0.98). However, phenotypic correlations were lower from 0.47 to 0.76 in males and 0.61 to 0.75 in females. Furthermore, BW records in the growing period (63 to 126 days of age) had moderate (male: 0.39, female: 0.53) to high (male: 0.87, female: 0.94) genetic correlations with pelting BW (210 days of age). The result of current study showed that RFI and BW in mink are highly heritable, especially at the late furring period, suggesting potential for large genetic gains for these traits. The genetic correlations suggested that substantial genetic gain can be obtained by only considering the RFI estimate and BW at pelting, however, lower genetic correlations than unity indicate that extra genetic gain can be obtained by including estimates of these traits during the growing period. This study suggests random regression methods are suitable for analysing feed efficiency and BW gain; and genetic selection for RFI in mink is promising.

Weaning of livestock mammals is often associated with digestive problems related to profound changes in the physiology of the gastrointestinal tract. This study was undertaken to study the developmental changes in the gastrointestinal tract of mink kits during the period of 34 to 59 days of age. Twenty-four mink kits from eight litters were included in the experiment. The dams and their litters were kept under standard farm conditions. The dams and the kits were fed a diet consisting of 48.1% protein, 40.7% fat and 11.1% carbohydrate of metabolizable energy. The mink kits were weaned at 42 days of age. At 34, 47 and 59 days of age, one male mink kit from each litter was euthanized. The activity of amylase, trypsin, chymotrypsin and lipase in the pancreatic tissue increased during the experimental period, whereas the activity of carboxyl ester hydrolase remained constant. The vitamin E concentration in plasma was stable from 34 to 59 days of age, whereas the concentration decreased in the liver. The stereochemical composition of α-tocopherol showed a steep decrease in the concentration of the biologically most active natural isomer in both plasma and liver through the whole weaning period, whereas the biologically less active 2S isomers showed a clear increase. The concentration of bile salts did not change during the experimental period. The villous height increased in the proximal part of the small intestine and decreased in the distal part, whereas the crypt depth was doubled in both the proximal and distal part of the small intestine. The mucin-staining area on the villi was markedly reduced during the experimental period but no change in the mucin-staining area in the crypts was observed.

The American mink Mustela vison has spread widely beyond its native North American range and is associated with problems for the conservation of native species because of its impact as both predator and competitor. We investigated the impact of feral mink on waterfowl in Lanín National Park, south-west Neuquén, Patagonia, Argentina, an area in which the predator is currently expanding. Statistically significant differences were observed in the number of waterfowl species at lakes without mink (7.3 ± SE 0.7) compared to those with mink (4.0 ± SE 0.6). Overall abundance of birds observed per day was higher at lakes without (104.2 ± SE 20.6) than with mink (21.2 ± SE 22.3). The great grebe Podiceps major, speckled teal Anas flavirostris, Chiloe wigeon Anas sibilatrix and red-gartered coot Fulica armillata were more abundant on water bodies without mink, and flocks of the ashy-headed goose Chloephaga poliocephala were larger in areas without mink. Other species, such as the white-tufted grebe Rollandia rolland, coscoroba swan Coscoroba coscoroba, black-necked swan Cygnus melanocoryphus, cinnamon teal Anas cyanoptera, Andean duck Oxyura jamaicensis and Andean gull Larus serranus were never observed in areas harbouring mink. We conclude that at least 12 of the 25 waterfowl species observed are sensitive to the presence of the mink, either being absent or having a lower abundance where mink are present.

We studied a group housing system as an alternative to the traditional pair housing of juvenile mink. The focus was on both the welfare and production of mink. The pairs were housed in standard mink cages, whereas the groups were in row cage systems consisting of three standard mink cages connected to each other. The welfare of the mink was evaluated by behavioural observations (stereotypies and social contacts), evaluation of the incidence of scars assumed to be caused by biting, and adrenal function (serum cortisol level after adrenocorticotropic hormone (ACTH) administration and adrenal mass). Feed consumption, pelt length, quality and price were used for comparing the two housing systems from the economic point of view. Although the incidence of scars showed that there might have been more aggressive behaviour among the group-housed than among the pair-housed mink, this was not observed unambiguously in behavioural observations, and, at least, aggression did not cause mortality or serious injuries to the animals as has been observed in some earlier studies. In addition, the housing system did not affect pelt size, and, although the quality of the pelts was slightly lower in the group than in pair-housed mink, there was only a tendency for lower pelt prices. The lower pelt prices in the group-housed mink might even be partially compensated for by the group-housed mink eating 10% to 20% less in the late autumn, due to thermoregulatory benefits, than their pair-housed conspecifics. The results on the frequency of stereotypic behaviour (but not adrenal function) suggest that the group-housed animals were possibly less stressed than the pair-housed animals. Group housing of juvenile farmed mink in a row cage system cannot be recommended before the effects on welfare and production are clarified in further studies.

Major nutrient and amino acid digestibilities were evaluated in experiments with dogs (Canis familiaris), blue foxes (Alopex lagopus) and mink (Mustela vison) using seven extruded diets containing different protein sources. Four dogs (German shepherd), four blue foxes and four mink were offered each of the experimental diets to determine apparent total tract digestibility. Average digestibility of crude protein (CP) in blue foxes and mink was similar, and lower than the corresponding value in dogs (0·834 and 0·831 v. 0·864) (P < 0·001). CP digestibility in blue foxes showed significant correlations with dogs and mink (P < 0·05), while no significant correlation was observed between dogs and mink. Average digestibility of most amino acids was significantly lower in blue foxes than in dogs (P < 0·001), whereas mink digested most essential amino acids at the same level as did dogs. Most non-essential amino acids were digested at a significantly lower rate in the mink than in the dog and the blue fox (P < 0·001). There were significant correlations in the digestibility of most amino acids between dogs and blue foxes, and between blue foxes and mink (P < 0·05). Correlations were significant between dogs and mink for the digestibility of most essential amino acids (P < 0·05) but not significant (P > 0·05) for several non-essential amino acids. Average digestibility of crude fat was high and similar among the species studied: 0·968, 0·967 and 0·959 in dogs, blue foxes and mink, respectively. Average digestibility of starch ranged from 0·971 in mink to 0·998 in dogs; significantly higher in dogs than in blue foxes and mink, and significantly higher in blue foxes than in mink (P < 0·001). It was concluded that digestibility determined with mink, blue foxes or dogs may be used to predict digestibilities in the other investigated species. However, both the characteristics of the protein sources as well as the individual amino acid studied will influence the difference in digestibility among the species.

The European mink Mustela lutreola is the focus of extensive conservation programmes whereas the American mink M. vison is exotic in Europe and a possible cause of European mink decline. Since both species, together with the European polecat M. putorius have similar hair and produce similar faeces, molecular techniques are essential for reliable species identification when disturbance is not appropriate. In this report a simple, cheap and reliable molecular method for the genetic distinction of mink is provided based on the amplification of the microsatellite locus Mel08 that results in a longer PCR product (436 bp) in American mink than in other mustelid species, such as the European mink (221 bp) and the European polecat (221 bp). Sequencing these PCR products revealed, in the microsatellite-flanking region of American mink, a CAN-SINE insertion of 213 bp that was absent in 22 species of the Canoidea superfamily tested. When the Mel08 PCR product is cut with restriction enzyme AciI and then run in an agarose gel, the restriction pattern observed is different in the three Mustela spp. The method was successfully tested with DNA amplified from a large sample of hair roots, thus making it suitable for non-invasive sampling.

Submerging in water is used by many species as a behavioral mechanism to reduce body temperature, and farmed mink have been shown to increase their swimming activity during summer months. Therefore we investigated whether a maintained, seasonally independent, high ambient temperature would lead to more swimming in farmed mink. Twelve mink were housed in a temperature controlled room and subjected to two periods of four different temperatures (8, 16, 24 and 32 °C) with each temperature lasting 4 days. Although some types of activities changed with changes in temperature, the total level of activity was not affected. At high temperatures, the mink did not show any increase in either swimming or stereotyped behavior. It is concluded that within the limits of the experiment, mink will not use submerging in water as a thermoregulatory mechanism.