IMPLICATIONS FOR DOMESTIC ANIMALS OF CYANOGENESIS IN SORGHUM FORAGE AND HAY

Sorghum species and their hybrids are widely grown for warm-season grazing and hay. Commercial hybrids are high yielding, capable of rapid re-growth and are efficient in the use of light, water and nitrogen. All sorghum species contain the cyanogenic glucoside, dhurrin. The cyanogenic potential of the forage is usually from 100 to 800 mg HCN equivalent kg^-1 on dry matter basis, with occasional samples exceeding 1000 mg HCN equivalent kg^-1.

The fatal poisoning of animals by forage sorghum is now infrequently reported in most countries. However the fear of farmers that their animals may be poisoned if they eat young sorghum has a very significant indirect effect on animal production. The cyanogenic potential declines as the plant matures but concurrently the nutritive value of the forage declines to sub-maintenance levels by the time farmers consider it "safe" to use. There is little evidence of chronic disease arising from diets of cyanogenic sorghum.

Detoxification of cyanide by the formation of thiocyanate reportedly accounts for 80% of ingested cyanide. The sulfur required for this process (possibly 1.2 g S per 1.0 g HCN) appears to be subsequently unavailable for protein synthesis in the animal. As the sulfur content of sorghum forage is frequently low, a dietary deficiency of this element may be induced. This manifests itself in reduced appetite and animal production.

Further development of disease and pest resistant genotypes with low cyanogenic potential, coupled with the use of sulfur and sodium supplements should enable farmers not only to live without fear of their stock being poisoned, but to obtain good animal production from this agronomically successful crop.