Management of Equine Metabolic Syndrome (EMS), the most accepted term for a syndrome of middle-aged obesity accompanied insulin
resistance (IR) and insidious-onset laminitis, can be challenging as it primarily involves client education and acceptance
to comply with dietary recommendations to effect weight loss. In addition, an understanding of the differences in nonstructural
carbohydrate content of various forages is important for appropriate dietary recommendations to be made. Next, implementation
of an exercise program for both at risk and affected horses (those with laminitis) is strongly recommended but can be difficult
to implement in equids suffering from laminitis. Although medications (thyroid hormone and metformin) and dietary supplements
(magnesium, chromium, vanadium, cinnamon, etc.) have been advocated to both assist with laminitis recovery and enhance weight
loss, data supporting use of these agents is limited.
Unfortunately for horses, syndromes of IR and cortisol excess (EMS [cortisol excess at the tissue level] and pituitary pars
intermedia dysfunction [systemic cortisol excess]) appear to be accompanied by alterations in the integrity of the basement
membrane between the epidermis and dermis of the laminar bed. Over time, weakening and degradation of the basement membrane
can lead to separation of the epidermal-dermal junction and development of laminitis. The most recently advanced term for
this type of laminitis is endocrinopathic laminitis. The mechanisms behind development of laminitis appear to be complex and
remain incompletely understood. Nevertheless, research over the past decade has provided new insights into some of these mechanisms
and may lay the groundwork for novel approaches to treatment of this devastating problem in horses.
Anatomy and physiology of the equine foot
The equine hoof is a complex epidermal-dermal structure evolved to support the large body mass of the horse. Although not
typically thought of as skin, the hoof is actually comprised of the same basic epidermal-dermal layers as skin. However, the
area of epidermal-dermal attachment has changed from a nearly straight junction to an interdigitating junction of primary
and secondary lamellae. This "laminar bed" markedly increases the surface area for attachment of the epidermis (hoof capsule)
to the underlying dermis, thereby, increasing the strength of attachment and capacity to support weight. The primary lamellae
(600-800 within each hoof) are long finger-like projections and interdigitation of the epidermal lamellae and the dermal lamellae
holds the hoof capsule onto the underlying dermis. However, the real strength of attachment is provided by the secondary lamellae
that consist of numerous short projections off each primary lamella. Secondary lamellae can be thought of as velcro-like projections
that provide incredible strength of attachment to the primary lamellae. At the junction of the epidermis and dermis lies the
basement membrane. The basement membrane consists of a lamina lucida, a lamina densa, and extracellular matrix. Within these
layers are several proteins including laminin, type IV collagen, type VII collagen, integrins, anchoring filaments, and others.
In addition to forming the supporting extracellular matrix of the basement membrane, these proteins, along with others, also
anchor or attach the secondary epidermal lamellae to the basal cells of the secondary dermal lamellae.