The problem where small carnivores are concerned is that (with a handful of exceptions) public collections are only interested in an ever-narrowing selection of species, and it is the private sector which keeps many species going. Moreover, there have been a number of occasions when populations of species which zoos *were* interested in breeding faltered precisely because the zoo world didn't want to work with private keepers who a) were far ahead in terms of husbandry experience and b) could have contributed fresh blood to the zoo programmes.
For instance, one of the most endangered native European species of small carnivore - surpassed only by European Mink - is the Marbled Polecat (the species in my avatar, as you probably know).... but despite several private collections keeping and breeding the species over the last decade or two, the captive population has dwindled to next-to-nothing due to a combination of mismanagement in some public collections, and a reluctance by others to work alongside the private sector.
Let me begin by saying I do not have a view of stamping out the responsible private ownership of exotic small carnivores but for the sake of argument I'll explain why I am opposed in principle to the keeping of small carnivores and private ownership.
Firstly there is the propensity of many small carnivores to either escape or be intentionally released from captivity and to establish themselves in the wild as incredibly destructive invasive species with regards to native fauna. For example, one of the reasons why the North American raccoon has established itself in Central and Southern Europe was partly due to it being kept in private collections as a pet (along of course with fur farms).
In the UK you have increasing numbers of people keeping and breeding small carnivore species like raccoons, skunks, coatis, raccoon dogs. There apparently have been a number of escapes of these animals and there are also believed to be small populations living in the wild. It has apparently been registered as a potential problem by your environmental governmental department DEFRA which suggests that there is a real risk of these becoming invasive species.
Secondly, I don't doubt that the private sector have had more success with small carnivores such as the marbled polecat in terms of husbandry than zoos and I believe that this is illustrative of the lack of interest shown by zoos towards smaller mammals in general and the bias towards larger more "charismatic" species. From reading online issues of the magazine "Zooquaria" I gather that there have been attempts by EAZA to try to encourage more interest in keeping small carnivores such as the European mink and marbled polecats in zoos. It would seem that zoos are still somewhat behind the times when it comes to this and perhaps do not view these animals as viable because their cryptic behaviour make them "poor exhibits" or they do not draw crowds.
Regarding the lack of collaboration between zoos and the private sector I can only say that this is a shame if different stakeholders that ostensibly should have a commitment to ex-situ conservation cannot come together and cooperate for the benefit of a threatened species (regardless of what is felt towards private ownership). I don't know why exactly this has happened because I am not familiar with the situation of marbled polecats in UK / Europe but perhaps it is due to institutional arrogance on the part of zoos and if that is the case then it is not good at all.
That said, on the subject of the marbled polecat and ferrets on general I would say that ex-situ conservation (whether by zoos or private individuals) through captive breeding programmes is only part of the solution here. Any ex-situ actions obviously need to be strongly integrated with in-situ actions within the range countries that address the drivers of its decline in the wild (use of pesticides and habitat destruction of the Eurasian steppes for agricultural conversion) because it won't matter if they are kept by every major zoo in Europe if they are functionally extinct in the wild.
For example, the famous and highly successful black footed ferret conservation programme in the USA (which didn't as far as I'm aware involve private owners) managed to bring the species back from the brink due to well managed and organized breeding programes within zoos and captive breeding facilities and in-situ actions such as reintroduction to the praries.
