Cyanogenesis in Bovine Rumen Fluid and Pure Cultures of Rumen Bacteria

Serviceberry browse (containing prunasin) was administered intraruminally to examine cyanogenesis in the bovine rumen. Maximum levels of hydrogen cyanide (HCN) in rumen fluid were observed .5 h after dosing, after which rates of HCN disappearance ranged from −.99 to −8.48 µg HCN•ml−1•h−1. Thiocyanate formation was detected in vivo and the degree of HCN detoxification was significant when it disappeared at slower rates. In vitro trials were also conducted to determine the effect of cattle diet on microbial degradation of amygdalin. Rates of HCN production from amygdalin varied by as much as 3- to 11-fold with rumen inocula from the same diet. Rate magnitudes in vitro were not closely related to cattle diets. In agreement, cyanogenic activity was found widely but unevenly distributed among pure cultures of rumen bacteria. Production of HCN from amygdalin occurred in 30 out of 68 strains of rumen bacteria tested. Thiocyanate formation was also detected in vitro when mixed rumen cultures were incubated with amygdalin or sodium cyanide.