Lesões na junção derme-epiderme do casco de vacas de aptidão leiteira de descarte com e sem sinais clínicos de laminite

Abstract

To detect and compare histopathological lesions in the dermo-epidermal junction of dairy cows with and without signs of laminitis. 39 cows from the same herd were classified in three groups: without any evident sign of laminitis and lameness (G1), and with hoof stress lines and other signs associated to laminitis and without (G2) and with (G3) lameness. Hoof samples were taken at slaughter, formalin fixed (24 h) and paraffin-embedded as usual. 5-m tissue sections were stained (H&E and PAS) and examined under light microscope. Congestion, hemorrhage and inflammatory cell accumulation in the dermis, irregularities in the basal membrane (BM) and alterations in the morphology of the epidermal cells were investigated for semiquantitative tissue evaluation. Individual tissue sections from the solar, axial and dorsal regions were blindly scored by the same researcher. Different regions within the same group and different groups within the same region were compared using on ranks analysis of variance (P<0.05). Signs of inflammation were detected in all regions of hoof in cows from the three groups. Within tissues, differences were seen only in congestion in G1 (solear > axial e dorsal) and in hemorrhage in G3 (solear > axial). Within groups, differences were not detected except by hemorrhage in the solear dermis (G3>G1 e G2) and in the dorsal dermis (G3>G1). Despite no clinical signs of laminitis, G1 cows presented the same level of lamellar inflammation and epidermal degradation compared to clinical laminitic groups. Generalizated dermal-epidermal junction inflammation and epidermal changes were a common finding in studied dairy cows even in those without clinical signs of laminitis. These findings indicates that the clinical signs of laminitis in dairy cows occurs subsequently to leukocyte infiltration and vascular fragility of the whole hoof dermal-epidermal junction.