Do you mean the normal type of hard fat you typically find covering the tenderloins? If so, I wouldn't worry.
A large number of the muntjac I have shot this year have been carrying significant hard fat along the spine, from the tenderloins right through to the diaphragm. In many cases some heavy layers of sub-cutaneous fat as well. I have had to "peel out" quite a few kidneys that were carrying between 90% and 100% fat coverage. Sometimes after hanging in the chiller I've had to almost dig the fat out!
The mild winter and abundance of food seems to have served them well.