Hoof wall growth is an amazing process. The hoof wall continues to grow throughout the horse’s life without the close connection with the coffin bone suffering from it. The hoof wall slides down over the coffin bone. There are two complementary theories on how this process works:
The theory of Dr. Chris Pollitt focuses on the connection between hoof wall and coffin bone. Influenced by pro-enzymes the available hemidesmosomes (see page 30) and protein fibres are broken down. This controlled destruction (and the reconstruction that follows) ensures that the connection remains strong while the hoof wall grows down at a cellular level.
The main focus of Dr. Robert Bowkerís theory is on keratinocytes. The secondary epidermal lamellae are made of these horn cells which are produced in the coronary band. While they grow down they produce the fibrous protein keratin. A keratinocyte becomes increasingly saturated with keratin. Eventually the cell dies and forms, with many other dead keratinocytes the hoof wall. Because of the death of the cells in the secondary epidermal lamellae their connection with the primary epidermal lamellae is lost. This continuous detachment and the production of keratinocytes enables the hoof wall to grow down.
Renewal of the entire hoof wall takes between eight and fifteen months. The heel is replaced much faster because the hoof is shorter at the back.