Possible Clues:

• Endless vigour on horseback causing decay
• Harry is after shortening energy switch - the type synonymous with circulation problems damaging the cells
• Tissue affliction common during the Civil War
• Necrosis of body tissue
• Tissue decay
• Group cuts lease scheme ending what could be a dead waste without a good blood supply
• Localised death of body tissue
• Localised death of cells
• Localised necrosis
• Backing horse lacking experience, we're told? That's rot