There are numerous plants that can be poisonous to horses. As a rule, horses avoid such plants because of their bitter taste. However, if they are contained in the dried state in the hay, they are often eaten. More information on the subject can be found in this blog from us to read.
Signs of poisoning include restlessness to apathy, shortness of breath, colic signs, circulatory failure or balance problems. If the poison is already attacking the brain, your horse may exhibit atypical behavior, such as running into stall walls.
The most important action is to prevent your horse from ingesting any more poison. You should also notify the veterinarian and move other horses away from the source of the poison. Until the vet arrives, you should offer your horse only clean water. If possible, note what the poisonous plant or poison looked like.