Barnyard Grass Poisoning in Horses

Barnyard Grass Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
Barnyard Grass Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Barnyard Grass Poisoning?

Barnyard grass, which is also known as barnyard millet, common barnyard grass and water grass, is a weed that has a flat stem and linear leaves. The leaves have a broad base that narrows at its tip. Its flower head can be reddish, purplish, pinkish or greenish and the plant can reach 2 meters in height, developing fully in 42-64 days. 

Barnyard grass contains nitrates which can lead to nitrate poisoning in horses should they ingest a large amount. While this type of poisoning is rare, it will cause severe symptoms when it occurs.

Barnyard grass (formal name E. crusgalli) contains nitrates and when ingested in large quantities can lead to severe symptoms and death in your horse.

Symptoms of Barnyard Grass Poisoning in Horses

Should your horse experience nitrate poisoning from barnyard grass, you may see the following symptoms:

  • Drowsiness
  • Weakness
  • Stomach pain
  • Diarrhea
  • Muscle tremors
  • Brownish discoloration of mucous membranes (the discoloration that can be seen in the vaginal membranes can indicate poisoning before the development of severe toxicity)
  • Shallow, rapid breathing
  • Rapid heart rate
  • Staggering gait
  • Convulsions
  • Abortion in pregnant mares (can occur at any stage of pregnancy)
  • Death can occur within 2-10 hours depending on the amount consumed and level of stress


Barnyard grass is not the only plant that contains nitrates. Other plants that may cause nitrate poisoning in your horse include:

  • Stork’s bill
  • Spear-leaved goosefoot
  • Witch grass


Causes of Barnyard Grass Poisoning in Horses

The cause of toxicity when ingesting barnyard grass are the nitrates that the plant contains. Typically, the quantity of nitrates in the plant would not be enough to cause toxicity in horses. In modern farming large amounts of nitrogenous fertilizers are used which can bring the level of nitrates in the plants to where they can be toxic to your horse.

In addition, the fertilizers can get into water that your horse drinks and contaminate it. Other things that may impact the nitrate level in plants are droughts and acidic soil. Nitrate levels will be higher in plants on cool, cloudy days and early mornings; the enzyme that is in the plants that will convert nitrates to other compounds will be less active without enough sunlight and warmth.

When experiencing nitrate toxicity, methemoglobin will be formed in the bloodstream of your horse, which will inhibit the carry and exchange of oxygen. This can lead to death as a result of your horse not having enough functional oxygen in his bloodstream.



Diagnosis of Barnyard Grass Poisoning in Horses

If you suspect that your horse is experiencing nitrate poisoning, whether as a result of consuming barnyard grass or another plant, you will want to seek immediate veterinary attention. It will be helpful to bring a sample of the plant that you believe your horse consumed as well as a sample of the water that he drank from. These can then be tested for nitrate toxicity, which will help in diagnosing your horse.

Upon conducting a physical examination of your horse, your veterinarian will ask you about the symptoms that you have noticed, when you first noticed them and any changes that have occurred. He will also conduct testing to see if there are toxic levels of methemoglobin in his bloodstream. Stomach contents can also be tested.



Treatment of Barnyard Grass Poisoning in Horses

Should your horse be experiencing nitrate poisoning, your veterinarian may administer an intravenous dose of methylene blue, which is found to be the most effective treatment. The dose will be from 2-7 mg/lb of body weight given as a 2-4% solution. Toxicity from the methylene blue can occur so it is important that this be handled by your veterinarian. Mineral oil may be given to your horse in an effort to counteract the nitrates impact on his gastrointestinal system as the veterinarian attempts to get the nitrates out of your horse’s system as soon as possible.



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Recovery of Barnyard Grass Poisoning in Horses

It is important that you do your best to keep your horse remain calm and not get over-excited, minimizing his stress. Should he survive barnyard grass toxicity, it will be important to work closely with your veterinarian to ensure the best outcome for your horse. Follow up appointments will likely be recommended so that your veterinarian can monitor your horse’s condition.

If your horse experience toxicity from barnyard grass, you will want to be sure that it and other plants with a significant content of nitrates are removed from the area where your horse grazes in order to avoid future toxicity. Nitrate toxicity can also occur from ingesting certain feeds (oat hay, alfalfa and Sudan grass) so those should be tested to ensure they are safe for animals to consume. As a result of nitrogen fertilization as well as drought conditions, the nitrate levels in plants can greatly increase; therefore, it is a good idea to test plants when they are going to be eaten to be sure they won’t cause toxicity in your horse.



Barnyard Grass Poisoning Questions and Advice from Veterinary Professionals

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