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The risk of poisoning from the grass is greater during severe conditions such as drought, trampling, and frost. During the growth stage of younger plants or a regrowth stage such as after mowing, it has excessively high levels of prussic acid which may be fatal for your horse. These grasses may also contain nitrates, and both these poisons together can form a lethal cocktail for your horse. Always monitor your horse carefully when grazing in a sorghum infiltrated paddock, and remove the moment it shows any signs of distress. Careful management of a pasture containing sorghum is essential if you plan to allow your horse to graze there. Consult your veterinarian and a specialist well versed in forage management for advice if you have sorghum grasses on your property.
Sorghum grasses contain prussic acid (cyanide), or hydrocyanic acid. The poison kills by preventing oxygen absorption in the tissues causing fatal respiratory problems.
The method by which this plant causes the problem is not that well understood but it does involve damage to the spinal cord and causes problems to the bladder and hindquarters of your horse. The poison doesn’t affect all horses, and not all react to the same extent as others, perhaps building a partial resistance to the condition. The continual release of urine dribbling on your horse’s legs can cause scalding. If your mare is pregnant, then abortion and malformation to the unborn foal may occur at any stage of the pregnancy.
Recovery depends on the amount of sorghum eaten and the time your horse has been allowed to graze. If you notice your horse showing any of the symptoms listed, call your veterinarian immediately. Prussic acid is a fast-acting poison and needs treatment right away. Removing your horse from the paddock is vital, then call your veterinarian to make a full examination. He will take a urine sample for analysis; the presence of cystitis is thought to indicate sorghum poisoning. Clinical signs may lead to further investigation, such as a study of spinal cord lesions but this will depend on the condition of your horse at time of examination. The veterinarian will also be able to identify the sorghum in the pasture.
Nitrate acid poisoning produces similar symptoms as prussic acid, so treatment and recovery depend on the correct diagnosis. If treated for nitric acid when it is, in fact, prussic acid poisoning, it can be fatal to your horse.
There is treatment available for sorghum poisoning. Because both nitrate and cyanide poisoning symptoms are so similar, the specialist’s advice is vital as the two treatments are totally different. Nitrate acid poisoning produces a dark chocolate brown blood, in contrast to prussic acid which produces a bright red blood. For prussic acid poisoned animals, sodium nitrate or sodium thiosulfate is recommended; it is an intravenous injection and if given before the heart stops, your horse may be saved.
Some veterinarians use methylene blue solution to treat both nitrate and prussic acid poisoning. For cystitis of the urinary tract, antibiotic treatment may be advised. Recovery depends on the amount of sorghum eaten and the time your horse has been allowed to graze. If your horse has reached the stage of ataxia (loss of coordination) then sadly recovery is unlikely.
Sorghum is hard to avoid, and is hard to know how much poison is in the plant at any given time. There are steps you can take to protect your horse. Avoid putting your horse into graze a paddock containing sorghum while it is hungry, ensure that they get plenty of roughage before going into the paddock. Easing its hunger first will decrease the amount of the first graze and will decrease the risk of ill effects.
Good management requires a close watch on your horse for the first 48 hours when introducing your horse to sorghum, and especially within the first two hours. One safeguard you can use is to provide a sulphur salt lick for your horse, as sulphur is a good detoxifying agent of cyanide. Observation and removing your horse at any sign of trouble and calling the veterinarian is the wisest course of action.
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