Transforming growth factor-β levels during second-intention healing are related to the different course of wound contraction in horses and ponies

Wound healing in horses is often complicated by wound infection, exuberant granulation tissue, and hypertrophic scars, especially when wounds are located on the limbs. Wound healing in ponies is less problematic, characterized by a greater degree of wound contraction and a more intense initial inflammatory response. Because both processes are influenced by transforming growth factor-β (TGF-β), it was hypothesized that the better wound healing in ponies was associated with different TGF-β profiles. A series of small wounds was created on the distal limbs and hindquarters of ponies and horses. Tissue samples were harvested on alternate days until day 13 postwounding, and levels of total and active TGF-β were determined. Levels of TGF-β were significantly higher in pony wounds than in those of horses. The TGF-β profile differed between limb and body wounds, with levels in body wounds decreasing at the end of the experiment and persisting in limb wounds. In ponies, the higher TGF-β levels can, to a large extent, explain the more intense inflammatory response and may explain the greater degree of wound contraction. Apparently adequate levels in the limbs fail to result in greater wound contraction, probably because of a stronger fixation of the skin. The persistence of elevated levels of TGF-β may result in the production of exuberant granulation tissue. Further research on the temporal patterns of the different TGF-β isoforms seems indicated, because manipulation of TGF-β levels appears to be a promising option for intervention in problematic wound healing in horses.