Biomechanics and histology of bovine claw suspensory tissue in early acute laminitis

Sampling of claw tissue. In each claw (1), 3 transverse cuts (A, B, and C) were made perpendicular to the dorsal claw wall. Cut A was made one-third of the distance from the tip of the toe to the junction between the horn capsule and the skin, cut B was 5mm proximal to A, and cut C was 3mm proximal to B. These 3 cuts resulted in 2 slices of tissue, A-B and B-C (2). On slice A-B, the horn was removed down to 2mm from the lamellae (D). In the dorso-abaxial wall, a cut (E) was placed 0.5cm abaxial to the crest of the dorsal claw wall and another cut (F) 10 to 12mm abaxial to E. The isolated tissue sample was separated from the underlying bone by a scalpel incision through the dermis as close to the pedal bone as possible. This sample (3) was processed for histological examination. In slice B-C, 3 parallel cuts (3mm apart) were made perpendicular to the most level surface of the dorso-abaxial claw wall (G). These cuts produced 2 adjacent rods of tissue consisting of horn, lamellar layer, dermis, and bone. The rods were separated from the rest of the slice by a cut perpendicular to the 3 cuts and through the bone (H). These 2 samples were obtained for mechanical testing (4).

Stress displacement curve generated by fixing claw tissue samples by horn and bone in a mechanical testing frame and loading to failure at a constant displacement rate of 2.0mm/s. Stress displacement curves were generated for each sample, and maximal support (MS) and physiological support (PS) were recorded.

A) Weight shifting and B) locomotion scores of heifers receiving oligofructose (OF) overload (17g/kg of BW) at 0h and in control heifers receiving tap water at 0h. In 3 heifers, it was not possible to perform locomotion scoring at 24h because of ataxia (3 missing observations). One control heifer showed consistent moderate lameness during the trial.

Transverse sections of tissue from the dorso-abaxial claw wall; right side is toward the pedal bone. Scale bars are 50μm. A, B) Sections of innermost tips of the lamellar layer stained with periodic acid-Schiff. C, D) Sections of the mid lamellar layer (halfway between the claw wall and the innermost tips) stained with hematoxylin and eosin. A) Control heifer, right hind lateral claw. Well-defined basement membrane, columnar basal cells with dark-stained nuclei (heterochromatin). B) Heifer killed 72h after oligofructose overload (17g/kg of BW), right hind lateral claw. Stretched lamellae, 1 to 2 cell layers thick, blurry and wavy basement membrane, cuboidal basal cells with rounded, light-stained nuclei (euchromatin). Insertion shows detached basement membrane at the tip of the upper lamella. C) Control heifer, left front medial claw. Columnar basal cells with dark-stained nuclei. D) Heifer killed 72h after oligofructose overload, left front medial claw. Cuboidal basal cells with rounded, light-stained nuclei positioned closer to the basal membrane. Color version available in the online PDF.

A) Means (±SD) of physiological support of claw suspensory tissue samples from all 8 claws of 6 control heifers, 4 heifers killed 24h after oligofructose overload (17g/kg of BW; OF24), and 6 heifers killed 72h after oligofructose overload (OF72). All groups included heifers from both herds A and B. B) Physiological support of claw suspensory tissue samples from all 8 claws of 5 heifers originating from herd A and 9 heifers originating from herd B. Both herd groups included control heifers and OF 24 and OF 72 heifers (n=225). Bars with different superscripts differ (P<0.0001).