Hi, well you have raised a very interesting question. It is a complex issue and since I have been recently volunteering at an animal rescue centre I might just shed light on this complex issue. Firstly I think it depends on the breed.There are many breeds like the Neapolitan Mastiff, the Caucasian Ovcharka which are strongly family oreinted and in particular to one owner. This owner should be a very dominant ( in relation to the dog), be assertive and show deemed superiority to the animal. If they have landed at the rescue, it could possibly be due to poor leadership qualities on behalf of the owner who has been unable to manage the breed not taking into account it's historical splendor or characteristics or it may land up due to several other issues. Attachment may depend on the breed and the individual in question. If the input of warmth, dominance ( to a certain extent) , love and affection is there and showered on the animal, then the animal is likely to reciprocate in return and will most likely readjust very soon trying to overcome its past. This has been the case with most rescue success stories. It is an extremely relative term and just as certain individuals are capable of adjusting to different situations very easily, the same could be said of canines too. If the breed itself has had a hardy history then it will adjust very easily to complex situations while if it is a recent creation or not had significant exposure to different conditions then it may not adjust well leading to behavorial issues like neurotic behaviour, unnecessary aggresion and the like. It may be extremely difficult to answer your question in a quantitative way but hope have shed light to this issue in a qualitative way. Best wishes, Vidya