Had it happen many years ago, a mate brought in a jill that had been left in season used his snipped hob over her the season after he went over all our jills, then when we came to breed a litter, non of the jills would take, we used different hobs and still nothing, a conversation with a vet and some lengthy research on his part proved they had contracted the ferret equivalent of a sti he gave me a course of antibiotics to put the jill on and heypresto a litter of kits was produced, after that I have only every used my snipped hob on my own jills