Lamellar cell death and proliferation are associated with restricted ambulation and preferential weight bearing in a...

To examine the effects of prolonged preferential weight bearing (PWB) and reduced ambulation (RA) on hoof lamellae using a nonpainful in vivo experimental model.

12 healthy Standardbred horses were housed in stocks continuously for 92 hours. A platform shoe was placed on 1 forelimb in the PWB group (n = 6) to increase the load on the supporting limb (SL) by approximately 10% bodyweight, whereas the RA group (n = 6) had normal weight bearing. Archived healthy horse (n = 8) samples were used as controls. Histomorphometry and histochemistry (terminal deoxynucleotidyl transferase dUTP nick-end labeling [TUNEL], caspase-3, and targeting protein for Xenopus kinesin-like protein [TPX-2]) results were analyzed using mixed-effects linear regression.

Lesions in multiple limbs from the PWB and RA groups included secondary epidermal lamellae elongation, cell death (mostly TUNEL-positive, caspase-3-negative parabasal keratinocytes), and basal cell proliferation (TPX-2 positive). Lesions were most severe in the PWB group SL, with significant increases (vs control) in mean (95% CI) primary epidermal lamellar (PEL) length (3.7 [95% CI, 3.5 to 3.8] mm vs 3.2 [95% CI, 2.9 to 3.4] mm; P < .001), secondary epidermal lamellae length (281 [95% CI, 235 to 327] µm vs 185 [95% CI, 155 to 215] µm; P < .001), TUNEL count (45 [95% CI, 30 to 60] vs 4 [95% CI, 2 to 5] positive cells/PEL; P < .001), and TPX-2 count (116 [95% CI, 46 to 186] vs 5 [95% CI, 3 to 6] positive cells/PEL; P < .002). Both TUNEL- and TPX-2-positive cell counts were increased in the RA group forelimbs versus control (P < .05).

Restriction of normal ambulation, even in the absence of increased weight bearing, caused lamellar parabasal keratinocyte death and structural derangement of lamellae.

Promoting ambulation, not just limb load relief, may be a critical strategy for preventing SL laminitis.