A rancher pulls into the clinic you are working at and rushes in to say his horse is having difficulty breathing. You assist the vet in examining the horse and note that the horse is in respiratory distress. He has dilated pupils and bright red mucous membranes. You are asked to pull blood for testing which you note is also bright red in color. Which of the following may cause this in the horse?
- Chronic Obstructive Pulmonary Disease (COPD)
- Walnut toxicity
- Cyanide toxicity
- Choke

Cyanide is a deadly poison. It exists in various forms like colorless gas like hydrogen cyanide, crystal form like sodium cyanide and others. It can damage the heart, lungs and brain. The symptoms associated with the cyanide toxicity involves dizziness, nausea and vomiting, rapid heart rate, restlessness, headache, dilated pupils, labored breathing and liberation of red mucous membrane from mouth and nose.

According to the above description, the cyanide toxicity is the correct option. As the horse condition is indicating towards the cyanide toxicity.