Have you ever wanted to know the poisonous or toxic plants that could be growing in your pasture? With the news of foals dying from the possible injestion of cherry leaves it is fresh in our minds now to consider what our own horses may be exposed to in the pasture. Use the lists below to learn more about the plants that may be growing in your grass!

What about the things you hear about bugs in hay?

Well, this is the place to find out about those problems . . . ones faced not just by horse owners, but farmers, cattle and dairy farms, goat keepers, hay growers and others. Some of these plants are even poisonous to you and me! So read on, then check your pasture!

Topics to be covered:

• Nitrate Poisoning
• Sudan Grass (sorghum)
• Blister Beetles
• Tall Fescue
• Johnson Grass

Used with permission (January 26, 2006)

Nitrate poisoning occurs in humans, cattle, goats, horses, dogs, birds, sheep and swine to a lesser degree.

The nitrate ion itself is relatively non toxic, it is when the nitrate is broken down in the digestive system that the trouble occurs.

Nitrate becomes nitrite which becomes ammonia, which becomes a protein. It is the nitrite phase in the stomach(s) where some of the nitrite can enter the bloodstream where it changes into a chemical that reduces the bloods ability to carry oxygen.

Oxygen starvation of the tissues occurs, along with a different process in which Prussic acid causes death of the tissues.

Nitrate poisoning happens when animals eat grass, hay, or drink water that contain large amounts of the chemical. This can come from plants, or from fertilizers used for farming.

Nitrates occur in most plants and in water, but sometimes the levels get so high as to become toxic. Grazing animals are usually poisoned by forage and hay. Nitrate consumption of as little as 0.05% of the animal's body weight may be lethal. Problems occur most often during cool temperatures, cloudy days or drought; also where heavy use of nitrate fertilizers occur. Nitrate formation increases when soil temperatures are 80 - 90 degrees. Low light (cloudy days) and night time causes nitrates to build up in plants, it is dispersed when sunlight hits the plants. The accumulation of nitrates in plants is a natural process. The plant gathers nitrogen through its root system and then stores it as nitrate in the stems. This nitrogen is later converted to protein in the leaves.

Horses can tolerate up to 0.50% nitrate in their total dry matter diet. A rule of thumb is to select hay for horses that contains no more than 0.65% nitrate ion on a dry matter basis.

Poisoning happens quickly, animals may be found dead before symptoms are noticed. Here is what to look for:

• Animal stays out of herd
• May collapse, fall in their tracks
• Weakness
• Unsteady gait
• Shallow and rapid breathing
• Rapid pulse
• Diarrhea
• Frequent urination
• Frothing at the mouth
• Coma
• Death accompanied by muscular reflex movements
• White of eye, tongue, lips may have a blue-brown discoloration
• Blood is chocolate brown in color
• Pregnant animals may abort

Other issues include animals ingesting plants that are "borderline" in toxicity causing abortion, reduced milk flow, lower weight gains, vitamin A deficiency.

Plants to watch out for:

Field Crops

• Alfalfa
• Millet
• Soy bean
• Barley
• Oats
• Corn
• Rape
• Sudan
• Fescue
• Rye
• Wheat

Vegetables

• Beets
• Lettuce
• Spinach
• Celery
• Mangles
• Squash
• Cucumbers
• Parsnips
• Swiss chard
• Kale
• Radishes
• Turnips

Weeds

• Bindweed
• Elderberry
• Russian thistle
• Blue-green algae
• Fiddleneck
• Smartweed
• Bull thistle
• Goldenrod
• Stinging nettle
• Burdock
• Lambsquarter
• Sunflower
• Canadian thistle
• Nightshades
• Velvetweed
• Carelessweed
• Ragweed
• Whitecockle

Other plants may have toxic levels under certain conditions.

Management Practices

1. Feeding rations high in carbohydrates will reduce and some times prevent losses from nitrate poisoning.
2. Control weeds that accumulate nitrates. Freshly sprayed plants may become more palatable, so defer grazing of sprayed areas.
3. During periods of cool or cloudy weather. avoid grazing a suspect area if possible. During periods of sunlight allow’ animals to eat large quantities of dry forage and then graze the area.
4. Test the nitrate content of forage when in doubt.
5. Distinguish nitrate poisoning from prussic acid poisoning or grass tetany, so the appropriate treatment may be administered.

Note: Oat hay mostened with water can convert nitrates to nitrites in a short time.

Members of the Sorghum family contain dhurrin, a glucoside that breaks down to release hydrocyanic acid also known as prussic acid. A sudden disruption of growth such as frost, drought or cutting, causes prussic acid to be released inside the plant at a more rapid rate. High prussic acid levels may be lethal to cattle and horses. Prussic acid will breakdown in one to two weeks, so material made into hay or silage is safe to use after curing.

Nutritional Concerns and Animal Health Hazards

Prussic acid poisoning is a concern in feeding Sorghum, Sudan grass, or Sorghum-Sudan grass hybrids. In the stomach, these compounds are converted into prussic acid, which is easily absorbed into the blood. High blood levels of prussic acid interfere with respiration and cattle can soon die from respiratory paralysis. Horses should not be allowed to graze these plants as they may develop cystitis syndrome. This condition looks like colic with accompanying bloody urine and can be fatal to horses. Affected animals may show a staggering gait and urine dribbling. Pregnant mares may abort. There is no treatment for this poisoning and poor prognosis of recovery.

Nitrate poisoning and formation of toxic silo gas can be a problem with Sorghum-Sudan grass. High nitrate levels are only a problem under abnormal growing conditions such as:

• High nitrogen fertilization caused by heavy fertilizer or manure applications or following legume plow down.
• Prolonged drought followed by rain.
• Any condition which kills the leaves while the roots and stems remain active will initiate accumulation of nitrates (frost, hail, grazing and trampling, or sometimes drought and overcast weather).

If you suspect high nitrates in the forage, have it tested.

Blister Beetles Epicautaspp., Meloidae, COLEOPTERA

Description (several species)

Adult - Blister beetles are slender insects 12 to 19 mm long. They have prominent heads and may be black with yellow margins or black and yellow striped.

Egg - The yellow cylindrical eggs are 1.3 to 1.8 mm long.

Larva - Each of the seven larval instars differ in size, shape and color. They can be 2.5 to 13 mm long, slender to plump, and white to yellow or brown. All instars have three pairs of short ventral legs and 12 body segments, excluding the head.

Pupa - The white, 10-mm-long pupae darken gradually beginning with the eyes.

Biology

Distribution - Blister beetles are found throughout the continental U.S. and agricultural areas of Canada. Although fairly common in North Carolina, they are infrequently pests of importance.

Host Plants - Blister beetles have a wide host range. Important vegetable hosts include potato, tomato, melon, eggplant, sweet potato, bean, pea, cowpea, pumpkin, onion, spinach, beet, carrot, pepper, radish, corn, and cabbage.

The beetles feed on alfalfa and soybean foliage. The real problem with blister beetles is their toxicity to livestock, especially horses, when accidentally eaten in feed. The beetles produce cantharidin, an irritant that causes painful blistering when the insects are handled. The cantharidin remains in the beetle's body even after it dies. That becomes a problem when alfalfa is swathed, during which dead blister beetles can be incorporated into the hay as it is made. Thus, livestock can accidentally consume whole beetles or their squashed remains when the hay is fed.

Horses are especially susceptible to blister beetle poisoning. Consumption of 25 to 300 beetles can kill a mature horse. Cattle and sheep are much less susceptible, but blister beetles will reduce digestibility of hay and may throw cattle off feed. Also, cantharidin is a stable compound that withstands decomposition even when it is dried or heated; the hay will keep its toxicity in storage.

Symptoms that include:

• Colic
• Blisters on the tongue and in the mouth
• Blood or intestinal lining discharge in stools
• Problems with urination
• Bloody discharge in urine
• Straining
• Elevated temperature
• Depression
• Increased heart and respiratory rates
• Dehydration
• Sweating
• Diarrhea

Because the toxin is absorbed and then excreted with the urine, severe inflammation of the urinary tract is a common sign of poisoning. Death may occur within 24 hours, and treatment with mineral oil by stomach tube is recommended but not always very effective. If blister beetle poisoning is suspected, contact a veterinarian immediately.

What can be done to avoid blister beetle problems?

1. Identify the species of blister beetles.
2. Grow your own alfalfa and maintain complete control over management practices, if possible.
3. Because blister beetle populations are not large until mid- to late summer, set aside first and often second cutting hay for use in feeding horses. Or consider purchasing first cutting hay from neighbors to use as horse feed.
4. Watch for beetles as you cut hay. Some species "swarm" in front of the harvester. Stop and let the beetles disperse before continuing.
5. Crimping and other conditioning increases the number of beetles that remain in the swath prior to baling. If possible, try to cut the alfalfa and put in swaths that can be straddled by the tractor to avoid crushing beetles in the windrow.
6. Eliminate weeds and cut the alfalfa before it reaches advanced bloom stages. Flowering plants attract the beetles that feed on alfalfa and weed pollen.
7. Insecticide treatments are available but must be applied with preharvest intervals in mind. If you treat with insecticides, be sure to allow enough time so that dying beetles fall out of the canopy to the ground where they burrow into the soil. Do not treat fields at peak bloom to avoid bee kills and losses to other beneficial species.

Because the larvae of many blister beetles in the genus Epicauta eat only grasshopper egg pods, these blister beetles are often associated with grasshopper outbreaks. Alfalfa grown near rangeland has a greater likelihood of blister beetle infestation.

Blister beetles are especially attracted to alfalfa and weeds (e.g., goldenrod) during bloom.

Guidelines for insecticide use in alfalfa are published annually in the High Plains Integrated Pest Management Guide. To purchase a copy, call the Colorado State University Cooperative Extension Resource Center, (970) 491-6198.

Insecticides are hazardous to pollinators, especially honey bees. Read, understand and follow all label directions, including pollinator protection statements.

Festuca arundinacea (grass family)

Toxicity Rating - Moderate to high, depending upon individual circumstance.

Animals Affected - Horses, cattle, possibly other ruminants.

Dangerous Parts of the Plant - Seed head, stem and leaf sheath.

Class of Signs - Reproductive problems, "poor doers", lameness, dry gangrene, fever, death.

Plant Description - This grass (fig. 15), often cultivated in wet pastures for forage or for turf, is a perennial, 3 to 4 foot tall clump grass with medium-wide leaves that are rough-ribbed on top. It has no rootstocks (rhizomes). The heads are open and many-branched. Escaped plants may be found along roadsides and in waste areas.

Signs - Toxicity is the result of an endophytic ("inside the plant") fungus, Acremonium coenophialum, which is believed to enable the grass to be more hardy and outcompete other grass species. The grass itself is not toxic. The fungus is passed in the seed, and is not transmitted directly from plant to plant.

In horses, pregnant mares are most at risk when eating fescue, since the alkaloids produced by the fungus inhibit prolactin release. Mares will have an increased risk of prolonged gestation, abortion, stillbirth, dystocia (difficult birth), foal mortality, retained or thickened placenta, no milk, and mare death (in foaling, or from a retained placenta).

Additional note: Fescue can accumulate nitrates under conditions of overfertilization (see the section on oats for more information on nitrate toxicosis).

First Aid - There is only supportive and symptomatic treatment once signs appear. A veterinarian can advise on treatment of more severely affected animals. Pregnant mares will be likely to need assistance when foaling and in the post-foaling period. Foals that survive will require supplemental colostrum. Management and prevention are the best means to minimize losses.

Safety in Prepared Feeds - The toxin remains active in hay.

Prevention - Fungicides do not work, so animal and pasture management are the only viable alternatives. Pastures can be tested for the presence and degree of fungal contamination, and reseeding may be needed. If reseeding the pasture is not an option, keeping the pasture short will prevent seed formation. Feeding other forages, such as other warm season grasses or legumes, will be of benefit. Fescue pastures can also be diluted with legume planting (red or white clover). Heavy fertilization may make the problem worse, especially in cattle. If fescue has to be used for mares, at least avoid feeding fescue hay or pasture during the last 30 to 60 days of gestation to minimize problems. Endophyte-free strains of fescue exist, although they do not grow as well as tall fescue with endophyte.

Sorghum halepense (grass family)

Toxicity Rating - Moderate to high.

Animals Affected - All types, especially ruminants.

Dangerous Parts of the 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 , 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 US 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.