The American mink (Neovison vison) is a species that experienced unprecedented ecological success in the 20 th century, which can be seen in both the dynamic increase in its zoogeographical range, and in its effective adaptation to ecological niches in new areas. The driving forces of this phenomenon include intensification and globalization of mink farming, which is accompanied by introduction and rapid spread of the species outside its natural range. The first observations of mink in the wild in Poland took place in the middle of the last century. Within 60 years, American mink colonized almost entire country and the process of invasion and colonization is still ongoing. The high rate of invasion and ecological success achieved by the populations from the introduction is possible due to the high ecological plasticity of American mink, its high reproductive potential, the availability of free ecological niche left by European mink (Mustela lutreola), extinct in many areas, and the frequent lack of natural enemies on the occupied territories. Dynamic geographical spread of allochthonous American mink is associated with a number of very serious ecological problems, primarily through predation, competition and aggression against indigenous fauna, as well as transmission of Aleutian mink disease virus. This results in fact that American mink is regarded as one of most dangerous invasive species in the world. In the absence of practical possibilities of its permanent eradication from Poland, local eradication programs on vulnerable areas (e.g. waterbirds breeding sites), as well as large−scale population size control, promotion of natural enemies and competitors, and improvement of living conditions of its prey−species are most recommended. The most important in monitoring and control programs of alien populations is limitation of farm−animals escapes and recognition of methods for their simple and unambiguous identification. Indisputable determination of the free−ranging animals origin would allow for taking the appropriate actions against owners of the unsafe farms. At the same time, implementation of a holistic and systemic approach to solve the problem of the presence of American mink in the natural environment would help to fulfil Polish obligations resulting from ratified international conventions and EU law.
The aim of the study was to determine the mechanical and geometric properties as well as bone tissue density of long bones in primiparous and multiparous dams of minks supplemented with ß-hydroxy ß-methylbutyrate (HMB) and/or 2-oxoketoglutarate (2-Ox) during gestation. Powdered 2-Ox was given at the daily dosage of 0.4 g/kg b.w. separately or simultaneously with HMB, which was administered at the daily dosage of 0.02 g/kg b.w. The study demonstrates for the first time that administration of 2-Ox and/or HMB to dams markedly influences bone tissue density and the mechanical and geometrical properties of mother's bones in minks. Moreover, it was demonstrated that the supplementation was more effective in the thoracic limb, which was comprehensively used in contrast to the pelvic limb. The mechanical parameters and bone tissue density significantly increased in the humerus in multiparous minks. Only such diet may provide satisfactory production results in the animals. Nutritional deficiencies occurring during pregnancies may trigger body's own reserves to cover the bone mass increase in developing foetuses and support milk production. This can prevent regeneration of dams' organisms, which negatively affects their reproductive performance. 2-Ox or HMB may be regarded as a protective metabolite when administered orally to minks, counteracting the negative influences of pregnancy and lactation periods on bones condition. Both simultaneous treatment with 2-Ox and HMB and their separate administration were equally effective.