ABSTRACT
Hooves were removed from heifers killed two weeks before calving (C-2), and four and twelve weeks post-calving (C+4 and C+12), and from age-matched maiden heifers. Segments were dissected from the anterior walls of lateral hind claws, to include horn, corium and bone, and the biomechanical properties were measured. There was reduced rigidity, both overall and at a physiologically appropriate displacement of 2 mm, and a greater displacement was required to reach initial and maximum support in the hooves of calving, compared with maiden, heifers. Histological examination revealed widened and distorted interdigitating laminae, progressing to C+12 in the hind claws, but with evidence of recovery in the front claws after C+4. Increased connective tissue strength from dorsal to ventral hoof segments was correlated with protein, proteoglycan, pro- and activated matrix metalloproteinase-2, and tissue inhibitors of metalloproteinases, and was inversely correlated with fat, water and collagen content. This implies that mechanical changes reflect alterations in the biochemistry of the connective tissue. This evidence supports the hypothesis that primary causal events associated with calving weaken the connective tissue of the hoof suspensory apparatus, leading to increased susceptibility to clinical lameness associated with sole ulcers and white line disease.
