The exact mechanism for the action for the effect of oxytetracycline on the foal tendon is not known. There is strong evidence at this point that it may be an effect on myofibroblasts (which are cells found in tendons, in addition to several other places). This may cause a change in the organization of collagen fibrils in the tendon making foals more susceptible to tendon (and ligament) stretching during weight bearing. This effect is mediated through a specific enzyme (MMP-1).