The frog corium in the back half of the foot is a 'W'-shape with the middle of the W being the cleft (rather than the 'U'-shape in the front half of the frog).
If the back half of the foot is spread the 'W' becomes flatter, even to the extent of apparently having no cleft.
From: Hoof@ECIR.groups.io <Hoof@ECIR.groups.io> on behalf of Maria Duran <mariaduran@...>
Sent: 29 April 2019 09:26
Subject: Re: [ECIR+Hoof] Frogs
Thank you so much Lavinia for this great explanation.
The questions were from two different horses but I perfectly understand.
About the unshoed horse is one from my riding school. I take care of him but have very little control over what can be done. He is 29 yo and has been unshoed now (only hinds) after all his life on shoes. He has very little depth in collateral grooves and has developed quite wide frogs but are very tender. He is clearly sore. What I wanted to know about his frogs is the lack of central sulcus. Do you know the reasons for a frog being flat without central sulcus? It is very weird to watch. Also is there something to be done about it? I am trimming his hinds as good as I can as they don't pay the farrier for the hinds.
Again thanks a lot for sharing your knowledge.