Digital Cushion Thickness, Transition, and Sole-Ulcer Risk

Sole ulcers are claw-horn lesions. Beneath the distal phalanx sits the digital cushion: cylinders of fat inside a collagen-rich connective-tissue framework. Together with the corium and the suspensory apparatus of the claw, it helps dissipate load before force reaches the horn-producing tissues. When that system is less able to spread load, the same standing day becomes a heavier mechanical challenge to the corium. Leave traction and wear to the flooring note, and hours on concrete to the standing-time note.

Ultrasound studies often measure the digital cushion together with the adjacent corium as sole soft-tissue thickness. A 2017 ultrasound study found that cows that experienced a sole ulcer or severe sole hemorrhage had sole soft tissues about 0.24 mm thinner than other cows, except when a sole ulcer was already present on that claw, when the tissues were thickened by about 0.53 mm — consistent with local inflammation. A follow-up analysis found thinner sole soft tissue ahead of a later sole ulcer or severe hemorrhage. A thin measurement can come before the lesion. A thicker reading after an ulcer appears does not mean the cushion is healthier.

Earlier studies linked greater body fat with thicker digital cushions, but newer prospective evidence shows that body condition alone does not reliably predict cushion thickness. Parity, stage of lactation, farm environment, lesion history, and tissue structure also matter. A 2009 study reported the body-fat association. The 2017 ultrasound study found sole soft tissues often thinner around calving than in late pregnancy, with a smaller backfat association that lesions could obscure. A 2024 prospective cohort of 2,352 cows on four UK farms found neither body condition score nor backfat thickness significantly associated with digital cushion thickness. Heifers ran thinner than multiparous cows until late lactation, and the thinnest point fell just after calving on some farms and in early lactation on others. A cow losing excessive condition through transition still deserves attention, because condition loss tracks lameness risk and wider transition trouble. The cushion does not simply thin whenever body fat is mobilized. Do not treat body condition as a proxy for cushion thickness.

The cushion is cylinders of fat embedded in a collagen framework, not a simple fat reservoir. A 2025 study found a lower proportion of type I collagen relative to type III in the digital cushions of cows with a history of lameness and hoof-horn lesions, and proposed that inflammation and remodeling can leave the tissue different after the original lesion has passed. Holding time, overcrowding, poor stalls, lock-up, slow parlor return, heat, and long walks all extend load under the pedal bone. A vulnerable cushion plus a long standing day is a different risk from the same cushion in a cow that gets enough lying time. The field lesson is that similar thickness is not the same mechanical protection.