Zebra Foal drawing

Ive taken the brave step and posted the start of this new drawing here despite not knowing if it will work at all!.It's taken a few days of roughing out to get the head-on shot of a zebra foal in the right proportions for the task in hand.ive now traced my finished sketch onto the prepared paper and started layering around the subject.so far ive layered twice in H and HB grade pencils.It's been quite time consuming not just because it's a relatively large piece for me but i'm struggling with a strain in the muscles of my right forearm after shifting heavy planters ackwardly around my garden at the weekend and my arm keeps getting too tight.The idea here is to try and re-create the backlit nature of my reference photo which will require clean white edges to the ears and face showing the protruding white hairs backlit.ive tried scratching out in places and i'm hoping that they will stand out sufficiently once the background tone is in place although i dont want to go too dark.there are also other areas on this image that are going to give me a severe test such as the ears and the fine hairs within.i havnt quite worked out how i'm going to surmount the difficulties that i'll encounter during this piece i'm just hopeful that the solutions will come to me as i go,hence my initial comment at the outset of this post.