43. JOHNSONGRASS

Sorghum halepense

(grass family)

TOXICITY RATING: Moderate to high.

ANIMALS AFFECTED: All types, especially ruminants.

DANGEROUS PARTS OF PLANTS: Leaves and stems, especially young plants.

CLASS OF SIGNS: Breathing problems, staggering, severe anxiety, convulsions, coma, death (may be very sudden).

PLANT DESCRIPTION: Johnsongrass (fig. 43), a coarse perennial grass, produces large, scaly rootstocks and grows in dense stands up to 6 feet high. Seed heads are large and loose. This plant grows commonly in the fields, fencerows, and ditch banks of the southern part of the state and is rapidly spreading northward. Once grown for dike stabilization or for hay, it is now classified as a "noxious" weed.

SIGNS: The toxic signs resulting from ingestion of Johnsongrass are due to the presence of cyanide in the leaves and stems. This toxicity is identical to that resulting from the ingestion of wilted or damaged cherry leaves. In normal, healthy Johnsongrass plants, the levels of free cyanide are low, and the plant can be consumed safely. Other members of this grass genus have been bred as grain or forage plants (milo, Sudan grass, etc.) and also have the potential to produce cyanide, although not as much as Johnsongrass. The young shoots are the most dangerous, and when wilted, trampled, herbicide treated or frost damaged, a great deal of free cyanide is liberated in the leaves. Upon ingestion, the animals quickly develop signs related to cyanide poisoning. Mature plants have much lower toxicity, and well-cured hay is relatively safe for consumption.

The most common occurrence of Johnsongrass toxicity is on pasture after the plants have been damaged somehow. Cyanide prevents the body from being able to utilize oxygen at the cellular level, so although the animals physically can breath, their tissues and cells "suffocate". After consumption, signs will manifest within a few minutes, but sometimes up to an hour may pass. The animals will try to breath more rapidly and deeply, and then become anxious and stressed. Later, trembling, incoordination, attempts to urinate and defecate and collapse is noted, which can proceed to a violent death (respiratory and/or cardiac arrest). If an affected animal is still alive 2 or 3 hours after consumption, chances are good that it will live. Under rare circumstances, a chronic cyanide toxicity can develop, which causes weakness and partial paralysis, but this is not a common occurrence. In the southwestern U.S., a syndrome affecting the urinary bladder and nervous system in horses has been reported after consumption of sorghum grasses. This disorder is called equine sorghum cystitis ataxia, and the animal is uncoordinated, has urinary incontinence (dribbles urine uncontrollably), and foals of affected mares may be aborted or be born with birth defects. The disorder can also cause death.

Johnsongrass, like other plant species, can accumulate toxic levels of nitrates, depending on fertilization practices. Nitrates are extremely toxic and can also cause death, especially in cattle, sheep and goats. Look in the section on oats for more discussion of nitrate poisoning. The signs of nitrate poisoning may be confused with cyanide poisoning.

FIRST AID: The clinical signs of cyanide poisoning tends to come on quite rapidly, and the animals may be found dead without much warning. If the animals are exhibiting toxic signs, call a veterinarian immediately. There is an antidote, but it needs to be given intravenously and within a few minutes of the onset of signs, and it is often impossible to get help in time. Prevent the animals (especially the unaffected animals) from eating any more of the grass or feed. Do not handle or stress affected animals any more than absolutely necessary, since this will worsen the signs. Also, affected animals are extremely stressed and may be dangerous to work with, therefore exercise caution so no human injury results. Similar recommendations exist for nitrate poisoning, although death usually doesn't occur as quickly as with cyanide.

SAFETY IN PREPARED FEEDS: When johnsongrass is dry, the level of cyanide is extremely low, so properly cured hay is safe for consumption. If the grass is used for silage or green chop, the levels of cyanide may still be quite high and potentially lethal. If the grass has accumulated toxic levels of nitrates, the hay, silage and chop will continue to be toxic. This may be fed in small amounts along with an adequate supply of good forage, although it would be best to discard feeds that are high in nitrates.

PREVENTION: Johnsongrass and other sorghums may be grazed safely throughout most of the growing season. Extra care must be taken when the grass is young, especially if damaged somehow. Animals should not be allowed access to the grass if these circumstances occur. Care must also be taken when fertilizing johnsongrass (as well as many other types of grasses) so as to not accumulate toxic levels of nitrates. Do not use johnsongrass as green chop or silage.