If fur has been seen on the x-ray and she doesn't groom Dennis, then you would think it must be her own. Or, it could also be that Dennis is shedding very small amounts of fur, which is amongst the hay that she is then eating. For example, Tui has been shedding white fur for months. Because it's pure white, it's very visible in the shed.
You might get some clues as to what it is once she starts to pass it. I don't think it's a stone out of the forage, as it would have been identified as such on the x-ray.
You might get some clues as to what it is once she starts to pass it. I don't think it's a stone out of the forage, as it would have been identified as such on the x-ray.