Dangers Caused by Drought: How to Protect your Horses
Dr. Gary Pusillo and Dr. Tsengeg Purevjav
Blue Springs, MO — September 10th, 2012— Drought creates a shortage of quality forages, grains, and water. During drought or overgrazing, horses may consume toxic weed species that contain harmful substances (Aiken, 1989).
While it is easy to recognize a shortage of available feed, it is difficult to visually see the dramatic changes that take place within the tissues that make up forage and grains. Drought conditions also result in close grazing and the ingestion of soil, microbial pathogens and parasites.
Concentrating potentially harmful substances; nitrates, prussic acid in all or some parts of plants total structure; may happen during droughts. Excessive nitrate accumulation in many plant species is more common after a rain during drought conditions.
Drought distressed plants often contain mold, mycotoxins, and wild yeasts, compounding potential health problems. This is especially true if mycotoxins have been produced in high enough quantities to challenge even the healthiest horses.
Toxic plants, nitrate, nitrite, prussic acid, and mycotoxin poisoning in horses may be suspected if one or more of the following conditions are observed:
1. Sudden onset of illness without visible cause.
2. Central nervous system disorders without fever.
3. Digestive system disorders (colic, absence of gut motility, sudden abdominal distention, diarrhea, constipation) without fever.
4. Rapid weight loss.
5. Frequent or prolonged prostration (stretched out, or lying down with the face downward).
6. Rapid Heart “action” and abnormal bulging blood vessels.
7. Breathing abnormalities
8. General distress
9. Slobbering, inflamed mucus membranes.
10. Swollen or discolored tongue.
Some plants tend to accumulate nitrates at greater rate; these include, but are not limited to commonly used summer annual grasses, corn, crabgrass, small grains, annual ryegrass, bermudagrass, Johnson grass, tall fescue, and some annual and perennial weeds commonly found in pastures and hayfields (Cash et al.2007).
Plant stress factors, such as hail, light frost, or plant disease can damage plant leaf areas and reduce photosynthetic activity. These stress factors can increase nitrate hazard in animals (Wright & Davison 1964).
Nitrate poisoning takes place when it is converted to nitrite in the digestive tract. When nitrate is absorbed into blood it changes the hemoglobin into a form (metmyoglobin) that cannot transport oxygen and the animal is asphyxiated (Bruningfann & Kaneene 1993).
Compared with ruminants, a considerably larger dosage of nitrate is required to cause clinical signs in horses (Schneider 1998). Forages are generally considered safe for horses if the nitrate concentration in the plant material is below 1.5 to 2.0% (Ball et al. 2007). Nitrates do not decrease over time in dry hay. This means that nitrates remain toxic months or even years later. If you suspect nitrates in your hay, make sure to test it (Taylor, 2010).
Horses can easily become overwhelmed by nitrates especially if their GI tract is compromised by molds, mycotoxins, and wild yeasts. Feeding a gut normalizer; Pro Balance by OrthoEquine/Durvet; is essential under these conditions.
Ingestion of nitrite can occur when nitrates in forages or water have been converted to nitrite by environmental microbes before horses ingest these forages.
Grazing stunted sorghum, sudangrass, and sorghum-sudangrass hybrids during drought provides concentrated cyanogenic glycosides which can decompose to free cyanide allowing it to become hydrocyanic acid, commonly called prussic acid (Akazawa et. al., 1960; Huff et. al 1985). Shattercane, and Johnson grass also produce dangerous concentrations (Huff et. al., 1985). Arrowgrass, velvetgrass, and white clover can also have prussic acid glycosides in their leaves. Chokecherry, pincherry, wild black cherry, apricot, peach, apple, and elderberry trees contain prussic acid glycosides in leaves and seeds.
Prussic Acid inhibits the release of oxygen from the hemoglobin of blood to individual cells; cellular respiration ceases and cells die rapidly due to hypoxia.
The best way to prevent a problem is through testing of all feeds for toxins; if that is impractical then feeding a daily gut normalizer such as Pro Balance by OrthoEquine/Durvet, is important to lessen the impact of drought.