Lecture 21 3/27/25 Flashcards
What is laminitis?
inflammation of the laminae of the hoof wall
What is the pathogenesis of laminitis?
-failure of the suspension system of the third phalanx (P3)
-mechanical injury to the sole corium and epidermis
What are the support structures for P3?
-laminar corium
-collagen fibers
-digital cushion
What are the characteristics of the laminar corium as a P3 support structure?
-interdigitations between the laminar corium and horn leaflets
-well developed at toe and abaxially
-weaker axially; axial wall is smaller
What are the characteristics of the collagen fibers/sling apparatus as a P3 support structure?
-originate in horny corrugations on the inner surface of the hoof wall
-insert into areas of the distal phalanx that have no periosteum
-pedal bone is “suspended” from wall of the hoof
-strong collagen fiber attachment between P3 and claw wall abaxially and distal cruciate axially
What are the characteristics of the digital cushion as a P3 support structure?
-found between back of P3 and sole of horn
-provides shock absorption
-composed of fat and connective tissue
What are the issues that can occur with the digital cushion?
-digital cushion is thinnest around peak lactation
-thin cows can have increased lameness
-increased lameness can cause thin cows
-small digital cushions can lead to increased mechanical injury to the corium
What happens if the caudal support of P3 breaks down?
sinking of P3 further into the hoof occurs
Which mechanical injuries can lead to laminitis?
-overgrowth of toe
-overgrowth of heel
-increased body weight/increased force on limbs
What are the characteristics of matrix metalloproteinases?
-allow for normal enzymatic remodeling of epidermal laminae
-accidentally recruited during laminitis; cause increased breakdown
Why is it important that laminitis does not occur in a state of vasoconstriction?
cooling the limbs can lead to decreased development of clinical signs
What are the non-inflammatory causes of laminitits?
-break down of collagen attachment of suspensory apparatus
-laxity of collagen attachment
-epidermal growth
What are the inflammatory causes of laminitis?
changes in circulation; especially associated with endotoxin
What is the pathogenesis of laminitis?
-vascular changes affect differentiation and proliferation of keratinocytes within germinal layer of epithelium
-horn cells are not properly keratinized
-reduced rigidity leads to poor quality horn
-horn is more susceptible to damage, excessive wear, and other claw diseases
What are the characteristics of acute laminitis?
-rare in cattle
-more common in feedlot cattle and first lactation dairy cows
-associated with grain overload and acidosis
What are the clinical signs of acute laminitis?
-increased RR
-increased HR
-runny stools
-decreased ruminal contractions
-may go down in the front
What is the treatment for acute laminitis?
recognize it as an emergency
-rumen lavage
-NSAIDs
-transfaunation
-supportive care
-soft surface for standing/increased bedding
What are the characteristics of subclinical laminitis?
-no clinical signs in early phase
-seen in dairy cows, feedlot cattle, and young bulls
-claw horn is weakened; leads to flaky soles
-P3 suspensory apparatus is weakened and can cause sole bruising
-may see subsolar hemorrhage
-increases the incidence of other foot disorders (white line dz, false sole)
What is the physical appearance of sole hemorrhage?
white line appears red
What are the other terms for chronic laminitis?
-founder
-slipper foot
What are the characteristics of chronic laminitis?
-mostly seen in older cows
-coronary band is darker and may have fragmenting horn
-rotation and sinking of P3
-concave dorsal wall
-sole and white line get wider
-poor prognosis
What is the physical appearance of chronic laminitis?
-claws widen, flatten, and have horizontal ridges
-toe tends to grow longer
-weight is displaced to the heel; toe lifts
What causes ulcer formation?
prolapsed corium and increased pressure at the area
Which ulcer is NOT associated with laminitis?
sole ulcers in the “typical place”