by: Darrell Rankins
PhD, Alabama Cooperative Extension System Animal Scientist

Numerous poisonous plants are present in many cattle pastures. However, most of the time cattle avoid these plants and they do not cause problems. On occasion, cattle will consume the plants to an extent that toxicity is exhibited.

Perilla mint. This plant is common throughout Alabama and most of the toxicity problems occur from now through the fall of the year. It is a square-stemmed plant that is 12 to 30 inches tall and as the summer progresses the top of the plant becomes a darker purple color. It is very common to find this plant in patches along the edge of where the woods and the pasture meet. It is also common under large shade trees and along the shaded area of buildings and structures that might be in a pasture. Cattle will consume the upper portion of the plant as well as the seeds that form at the top of the plant. It will affect mature cows as well as younger animals. The primary symptom is a breathing problem. The afflicted animals will exhibit an emphysema-like condition where they have difficulty in exhaling and they may also have an elevated body temperature. For treatment consult your veterinarian. The plant is easily killed by many of the available broad-leaf herbicides and can be quickly brought under control. However, if the plant is ignored it will spread to a greater area each year.

Blue-green algae. This is a problem in stagnant ponds that have high organic matter content. Ponds that are simply water entrapments and are not fed by a spring or creek are generally the most likely to produce this problem. Because of the hot weather cattle spend a lot of time in the pond thus creating a high organic matter content. When the water temperature gets high these conditions are perfect for a blue-green algae "bloom." As these organisms die they release potent toxins into the water that can cause severe poisonings in cattle that drink the water. The poisoning is typically characterized by photosensitization and eventual liver failure. The photosensitization is characterized by skin lesions in lightly pigmented skin. It is very similar to a severe sunburn. Eventually the liver fails and the animal dies. Effected animals should be moved into a shelter where they are out of the direct sunlight and the veterinarian contacted. All other animals should be moved so that they do not have access to the stagnant pond. Algae in ponds can be reduced with copper sulfate and other pond treatment protocols.

Nitrates. Whenever hay is harvested during drought conditions the potential for increased nitrate concentrations exists. This problem will not be manifested until this winter when you feed the hay. If there is any doubt about the potential for nitrate concentrations, have the hay tested. Take a representative sample of the hay in question and send it to the Forage Testing Laboratory at Auburn. Indicate that you want a nitrate analysis and the fee is $6.00 per sample.

Pay particular attention to the way in which the nitrate concentrations are reported. Some labs report it as nitrates (NO3) and some report it as nitrate nitrogen (NO3-N). Nitrate nitrogen is how the AU Forage Lab will report it. To convert nitrate to nitrate nitrogen multiply the nitrate level by .23.

The following guidelines can be used once the level of nitrate nitrogen has been determined.

0 to 575 ppm NO3-N: Generally considered safe.

575 to 1150 ppm NO3-N: Use caution. Allow cattle to graze this forage for less than two hours after having access to hay for three to four hours. Do not feed with liquid feed or other non-protein nitrogen sources. Be careful with pregnant and young cattle.

1150 to 3450 ppm NO3-N: Dangerous level. Limit to one-fourth of the total intake. Adequate levels of Vitamin A should be provided.

Greater than 3450 ppm NO3-N: Potentially fatal. Can be used in very limited amounts but will need to be mixed with other feeds or hand-fed.

Animals experiencing nitrate toxicosis may show signs of labored breathing, muscle tremors and a staggering gait, after which the cow falls down, gasps for breath and dies quickly. The cause of death is lack of oxygen and the membranes of the eyes and mouth are usually bluish while the blood will be reddish brown and turns brighter red once exposed to the air. If prompt action is taken some animals can be saved so it is advisable to call a veterinarian as soon as possible.

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