Are laminitis and founder the same thing? FAQ

Are laminitis and founder the same thing?

No. Laminitis can, but does not always produce founder.

Lamina: A thin flat layer or membrane
itis: Inflammation
Laminitis: Inflammation of a lamina
Founder: Sink
When we use the term "laminitis" regarding horse's feet we are speaking of inflammation of the tissues that bond the hoof wall through connective tissue to the coffin bone. There are two major types of laminae that create this bond: sensitive and insensitive.
The image above shows the laminae on the inner surface of the hoof wall. The insert magnifies the laminae, showing some of the hoof wall (black and yellow at top), the insensitive laminae (black, non-living), sensitive laminae (red, living), as well some of the fleshy interior of the foot (also red). The insensitive (black) laminae "interdigitate" with the sensitive (red) laminae. We refer to this as the lamellar bond.
The insensitive laminae are arranged in long thin flat "leaves" along the inner surface of the hoof wall. These laminae are non-living, insensitive tissues. They are part of the hoof wall and grow from coronary band to ground surface as does rest of the hoof wall.

The sensitive laminae are the reciprocal living counter part to the insensitive laminae. These are living tissues that interdigitate with the insensitive laminae forming a remarkably strong and durable "connection" between the hoof wall and the coffin bone.

As with all living tissue the sensitive laminae can become inflamed. When this happens the horse is experiencing laminitis. The lamellar tissues are extremely durable and forgiving, but at some point a threshold is reached beyond which the ability of the sensitive laminae to continue "holding on" to the insensitive laminae is compromised.

The moment that the bond "relaxes" or gives up altogether, permitting the coffin bone to "sink" relative to the hoof wall, founder occurs. Founder begins when the lamellar bond fails. The important change that occurs with founder is that the horse is no longer "connected" to his hoof wall in as healthy a fashion as he was prior to experiencing founder.

This FAQ tries to answer the question: Are laminitis and founder the same thing? Determining if an individual horse has progressed from laminitis to founder is quite another question. The level of pain a horse demonstrates does not necessarily indicate either laminitis or founder. Some horses show tremendous pain while they are laminitic, and others show very little. The same may be true for foundering horses. Even radiographs may not be very helpful. In the absence of prior films, it can be difficult to determine if radiographic evidence of anatomical changes is recent. Changes seen may be from past episodes of disease. Small "amounts" of founder may be difficult to image radiographically in the best of circumstances. Creating high quality radiographs for the purpose of evaluating laminitis/founder requires some skill and experience. Because the consequences of laminitis/founder can be so grave, we recommend great care be taken while evaluating a suspected horse. The treatments offered the laminitic horse may be completely different from those offered the foundering horse.