we have been caring for a feral colony and just recently one had a foot injury
,as they were quite used to us we started feeding chicken chunks to coax him in a cat carrier(nobody could borrow us a trap)we tried chicken and stewed steak,even irish stew!!!!
we put meat fat( called dripping or lard over here)mixed with the stewed steak,it took us two weeks to get him in(voluntarily)in the process all the other ferals thought it was christmas come early and they all got a little more fatter,
two days later an outbreak of cat flu swept through the colony and some started to lose weight (their little throats must have been so sore) a couple went missing for a couple of days,but they are all now getting over it,i think if they hadn't had that extra fat reserve just before,i do not think they would have come through it,
so i do not see any harm in a bit of meat fat to supplement their diet,you never know when they will need those extra reserves,especially now with the onset of winter