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Sorghum Poisoning in Horses

(Sudan Grass Poisoning)

By

Barry R. Blakley

, DVM, PhD, University of Saskatchewan

Last full review/revision Jun 2021 | Content last modified Jul 2021

Sorghum species are drought-tolerant plants with a high nutritional value related to protein, fiber, calcium, potassium, phosphorus, and antioxidant content. Unfortunately, the plants may produce neuropathic and teratogenic manifestations if consumed by animals. Sorghum poisoning has occurred primarily in the southwestern US and Australia. The syndrome is reported almost exclusively in horses, although a similar disease has been reported in sheep and cattle. Lathyrogenic nitriles such as beta-cyanoalanine, cyanogenic glycosides, and nitrates have been suggested as causative agents. The syndrome develops in horses after they have grazed hybrid Sudan pastures for weeks to months, and axonal degeneration and myelomalacia in the spinal cord and cerebellum develop. (Also see Cyanide Poisoning Cyanide Poisoning read more .) Consumption of the seed will not produce the disease.

Sorghum poisoning is characterized by caudal ataxia or incoordination, cystitis, urinary incontinence (which predisposes both male and female horses to cystitis), and alopecia on the hind legs due to urine scalding. The loss of urinary bladder function is related to axonal degeneration of spinal cord neurons. Incoordination may progress to irreversible flaccid paralysis. Deformities of the fetal musculoskeletal system (ankylosis or arthrogryposis) and abortion may occur during late pregnancy.

Diagnosis is based on the analysis of urine for evidence of cystitis and on the characterization of spinal cord lesions associated with degeneration in the cauda equina and sacrococcygeal nerve roots. Analysis of forage for cyanide content may be helpful, although cyanide concentrations vary considerably over time. The cyanide content is influenced by frost, drought, and herbicide application. Although fatal poisoning (toxicosis) is infrequent, the impact on reproduction is the primary concern. Consumption of sorghum hybrids with low cyanogenic potential, or restriction of access to sorghum grasses may limit the incidence. Alternative feed sources, rotational grazing, and feeding of fully cured sorghum feeds will reduce cyanide exposure. Dietary supplementation with sulfur may be beneficial. Affected horses often die from pyelonephritis. Treatment with antimicrobials may be helpful, but full recovery is rare if ataxia has developed. Grazing on pastures containing sorghum plant species, particularly related to regrowth conditions, is not recommended for horses.

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