I have kept ferrets from around the age of 14, in those early days I also had kestrel's and barn owls, therefore the ferrets at that time were fed the same, dead day old chicks, dry food was'ent available or heard of back then, and I never ferreted rabbits, or gave other foods, yet most of my fert, lived to ages of 6yrs plus
only time I had a fert die, was a jill had come into season, while I was on holiday with the school, and those left to look after them, fed them, but did'nt clean cage, and infection had got her via the vulva
as for "fluff" in the throat, how does that differ from