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This gait abnormality is often referred to as stringhalt. Eating catsear (flatweed or false dandelion) does damage to the nervous system which creates such limb pain that the horse is unable to maneuver certain steps comfortably. Lifting the back legs much more than necessary seems to give the horse a relief from that pain when backing up or turning. The toxin responsible for the poisoning is still unknown, but the plant (weed) known to cause the condition is catsear, which looks a lot like a dandelion only larger.
The catsear weed resembles a dandelion in many ways, which includes the rosette of long, hairy, toothed leaves at the base and the yellow mum-like flowers. In fact, the seeds are even very similar to dandelions with furry heads that are like parachutes to distribute them all over when the wind blows. Unlike many poisonous plants, the catsear is palatable to horses and they will look for it when they are turned out in an area where these plants have been known to be plentiful.
Catsear (Hypochaeris radicata) poisoning may present as an exaggerated stepping shown in one or both of the back legs when backing up, turning, or trotting.
The symptoms of catsear poisoning in your horse are hard to mistake. There are not many features of this condition that can be mistaken for something else. The toxin in the plant causes the back legs to step abnormally high when turning, trotting, and backing up. Apparently, the axonal nerves that control the pelvic limbs are affected to a degree that makes doing these activities painful and is very stressful to the horse.
The cause of Catsear poisoning is eating Hypochaeris radicata (Catsear) plants. The actual toxin in the plant is still unknown, but the effect is thought to be caused by nerve damage or degeneration. This condition can be prevented by carefully maintaining the pastures where your horse is allowed to graze.
Obtaining and discussing your horse’s history will be the first diagnostic step taken by your veterinarian. It is best to see a veterinary professional that specializes in equines because they have more training in all things related to horses. Be certain to let the veterinarian know whether your horse has been ill lately and whether you have given him any medications. If you have medical and immunization records, you should have them accessible. The veterinarian will take your horse’s vital signs and do a complete physical assessment.
Laboratory tests will need to be done to rule out other conditions such as upward patellar fixation, peripheral neuropathy, fibrotic myopathy, and shivers. Additionally, electromyography (EMG) can give a definitive diagnosis by analyzing the activity in the long digital extensor muscle during hindlimb flexion. An ultrasound, digital radiographs (x-rays), CT scans, and an MRI will be done as needed.
There are medical and surgical treatments which include medication, special diets, and surgery.
Drugs that are commonly given to horses with catsear poisoning include diazepam or phenytoin for convulsive reflexes, sedatives, and muscle relaxers to reduce anxiety and help with muscle contractions.
Many horses affected by catsear poisoning are reliant on the pasture for all of their nutrients and that is a problem. Horses need to have nutritional feed in the stall with them so they are not so eager to eat unsuitable forage in the paddocks and pastures, though it is known that catsear is a palatable find. The veterinarian may walk the paddock and evaluate the terrain.
The veterinarian may recommend tenotomy surgery to remove a part of the long extensor tendon over the hock. This is useful in cases where the horse is unable to walk anymore.
It will take many months of physical therapy and a lot of work for both you and your horse to overcome catsear toxicity. In fact, even after all the treatments your horse may never be back to normal in some cases. Chances of complete recovery are about 60% depending on the severity of the nerve damage.
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