Tropical Grasslands (1989) Volume 23, 193–202

CONSEQUENCES FOR ANIMAL PRODUCTION OF CYANOGENESIS IN SORGHUM FORAGE AND HAY — A REVIEW

J.L. WHEELER and C. MULCAHY

CSIRO Division of Animal Production, Pastoral Research Laboratory, Armidale, N.S.W. 2350

Abstract

Sorghum has several desirable attributes as a summer forage crop and interest in using it for hay is increasing. All sorghum forage has the potential to release hydrogen cyanide (HCNp) when eaten by ruminants. Factors affecting the HCNp are enumerated and the possible role of cyanogenesis in pest and disease resistance is briefly reviewed. Consequences discussed are frank poisoning and the factors affecting it, the effect of fear of poisoning on utilisation practice, reduced acceptability of the forage to animals, and the induction of sulfur deficiency. The advantages of routine supplementation with salt and sulfur are noted.
The process of hay-making may destroy much of the enzyme that mediates the release of HCN but normally it does not greatly reduce the content of cyanogenic glucoside. As the enzyme is present in the rumen and the intake of dried forage is more rapid than that of fresh forage, sorghum hay may be more toxic than fresh sorghum especially if the hay is ground and pelleted. Ensiling, however, normally reduces the toxicity of sorghum because HCN is released during the acid fermentation. It is questionable whether hay should ever be made from failed grain sorghum crops unless the product can be analysed and test-fed.

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