The Collaborative International Dictionary of English v.0.48:

Renning \Ren"ning\ (r?n"n?ng), n.
   See 2d Rennet. [Obs.]
   [1913 Webster]

         Asses' milk is holden for to be thickest, and therefore
         they use it instead of renning, to turn milk.
                                                  --Holland.
   [1913 Webster]